This April, Vox’s podcasts are teaming up to cover some of the most important issues threatening life on Earth. From sustainability to biodiversity to straight-up cool things about the natural world, we’ll focus on our planet and its limits in episodes throughout the month. 

We’ll tell stories about how a kayak changed one life to the trouble with gas stoves to how rising temperatures will change what food we have available to eat. And, of course, we’ll dive deep into policy — including a Weeds palooza with four promising white papers on the details of how we can bring down greenhouse gas emissions.

Tune into Today, Explained, Vox Conversations, The Weeds, Unexplainable, Worldly, Future Perfect, Recode Daily, and Vox Quick Hits to hear new Earth Month episodes every week. Below, you’ll find a guide to every episode. Want to share all of the shows with your friends? Simply point them to vox.com/earthmonth.

Climate change

The Weeds: White-paper palooza | 4/13

It’s an all white paper episode, folks. Vox climate reporter Umair Irfan joins Matt and Dara to take on three research papers all concerning climate change: first, on the social costs of carbon; then on the disparate effects of temperature rise on a diverse array of geographic regions; finally, on global migration due to climate change.

Future Perfect: Engineering our way out of the climate crisis | 4/14

In an ideal world, cutting carbon emissions would be enough to stop global warming. But after dithering for decades, the world needs a back-up plan. Kelly Wanser is the leader of a group called SilverLining that works to promote research into what it calls “solar climate intervention.” Also called “solar geoengineering,” this approach involves putting particles into clouds that reflect back the sun, directly cooling the earth.

It’s a novel and potentially hazardous policy — but one that Wanser and other experts argue could hold a lot of promise as the world braces for catastrophic climate impacts. Wanser and Vox’s Dylan Matthews discuss how solar climate intervention works, how it could be implemented, and where it fits in with the goal of cutting emissions.

Today, Explained: Peanut butter and jellyfish | 4/19

In partnership with Eater, we will take a look at how rising temperatures will change our food systems: from poisonous lettuce to the merits of jellyfish when all of the clams die.

Vox Quick Hits: Tell Me More: Will the superpowers unite on climate? | 4/19

The United States and China play leading roles in the global response to climate change: Together, they account for 43 percent of global carbon dioxide emissions. And it’s not just actions in their own countries that matter; they are highly influential in the world, too. Many industrialized countries look to the US for cues on climate action, and many developing countries look to China.

Recode Daily: The gas stove myth | 4/19

You may be under the impression that a gas stove is better than an electric stove, but that’s because the fossil fuel industry wants you to think that. Decades’ worth of campaigning and messaging has convinced the average renter and homeowner that gas stoves are the preferred choice. But really, they emit harmful fumes into your own home.

Today, Explained: The case for climate optimism | 4/20

In 2019, David Wallace-Wells wrote a book called The Uninhabitable Earth. Just two years later, he’s feeling hopeful — thanks to the world’s biggest polluters.

Vox Quick Hits: Tell Me More: The blunt truth about weed farms | 4/20

Commercial marijuana production is increasing as more states legalize recreational use, but indoor weed farms have a significant impact on the climate. In fact, a recent study found that just an eighth of weed has a 41-pound carbon footprint. The solution? Finding a more climate-friendly way to grow marijuana, such as outdoor farms.

Future Perfect: Should I still have kids if I’m worried about climate change? | 4/21

Climate scientist Kimberly Nicholas co-led a study that showed the single most effective thing an individual can do to decrease their carbon footprint is have fewer kids. Despite that finding, she still says that people who really want to have kids should go ahead with their plans. She explains how she squares that circle to Vox’s Sigal Samuel, and the two discuss how to think about the decision to have kids or not and how to make meaning in a warming world.

Worldly: How Nigeria explains the climate crisis | 4/22

In a very special Earth Month episode, Zack, Jenn, and Alex use Nigeria as a case study to uncover the deep reasons why it’s so hard for the world to quit fossil fuels. Nigeria is a country deeply threatened by climate change, but it’s also one with a major oil industry that hopes to lift millions out of poverty — a feat that has never been done without some degree of reliance on dirty energy. The team explains how these barriers affect the prospects for mitigating climate change in both Nigeria and globally, and talk about what solutions might help overcome these barriers. 

Today, Explained: Is nuclear energy good or bad? | 4/22

Where does nuclear energy fit into the climate conversation? Why is it taking a bigger role in some countries’ energy policies and why is it not in Biden’s plan? Listen to the Atlantic’s Robinson Meyer explain the arguments and then decide for yourself. 

Recode Daily: If an atmospheric scientist had a billion dollars | 4/22

Billionaires like Jeff Bezos, Elon Musk, and Bill Gates have made pledges to commit their earnings to saving our heating planet, but are they going about it in the best way possible? And do we want the fate of our planet to rest in their hands? Atmospheric science professor Kerry Emanuel explains how he’d spend a billion dollars.

Future Perfect: Sucking the carbon out of the sky | 4/28

A conversation with Akshat Rathi, a PhD chemist turned Bloomberg reporter and expert on carbon removal as an industry. What does carbon removal even mean? Can we even do that? How can this be used, particularly by the oil industry, for better or worse?

Clean energy and technology

Vox Conversations: How to replace everything in the industrialized world | 4/15

If the entire world’s energy infrastructure is going to be switched over to clean energy sources in a matter of decades, that’s going to require an enormous amount of building; from electric vehicles to heat pumps to batteries to mass timber buildings to microgrids to electric cooktops, and on and on. It turns out we know quite a bit about how to accelerate technologies along those curves, and which technologies need help from which kinds of policies. Climate writer and Vox contributor David Roberts talks with Jessika Trancik, Associate Professor at the Institute for Data, Systems, and Society at M.I.T.

Today, Explained: It’s electric! | 4/21

Norway has lapped the world in adopting electric vehicles. Vox’s Umair Irfan explains how the US might catch up. 

Recode Daily: The surprisingly exciting future of batteries | 4/23

Batteries are crucial for the transition to an economy powered entirely by renewables. David Roberts, writer of the Volts newsletter, explains how lithium ion batteries will be used for a lot more than just electric cars. 

Sustainability

Recode Daily: Bitcoin’s inconvenient truth | 4/20

From cryptocurrencies to artificial intelligence language algorithms, big computing takes a lot of energy. Some transactions using cryptocurrency require as much energy as an EU resident uses in a month. Is there a way to make big computing greener?

Recode Daily: Is remote work better for the environment? | 4/21

Working from home seems like it could be great for the climate. You don’t need to drive a car to work, and companies won’t need to heat and power large offices. But as Professor William O’Brien explains, the reality is much more complicated, and without proper planning, remote work may lead to greater emissions in the future.

The Weeds: How to build better transit infrastructure | 4/23

Matt Yglesias is joined by professor and transit researcher Eric Goldwyn to talk about why transit projects in the U.S. often fail. They discuss several high-profile cases, including the Second Avenue subway line in New York, the Green Line Extension in Boston, and the DC Streetcar. Why do cities spearhead redundant transit lines on top of existing rights-of-way? Why do cities in other countries spend so much less per mile on transit than American cities do? And, how can the political opposition to mass transit be met, to build the more accessible and environmentally-conscious transit infrastructure of the future?

Vox Quick Hits: One Good Answer: Why it’s hard to talk about sustainability in fashion | 4/28

Only one out of the dozen or so most commonly cited facts about the fashion industry’s huge environmental footprint is based on any sort of science, data collection, or peer-reviewed research. The rest are based on gut feelings, broken links, marketing, and something someone said in 2003.

If we’re serious about recruiting the fashion industry into the fight to save our world from burning, these bad facts do us all a disservice. They make fashion activists look silly. They allow brands to wave vaguely at reducing their impact without taking meaningful action. And they stymie the ability to implement meaningful regulation, which needs to be undergirded by solid data.

Biodiversity

Vox Conversations: The complicated history of wildlife conversation | 4/22

Vox environmental reporter Benji Jones talks with journalist and author Michelle Nijhuis about her book Beloved Beasts: Fighting for Life in an Age of Extinction. They talk about the history of the conservation movement and its many characters, the standout successes and ugly truths, and why, even with millions of species under threat, there’s still reason to hope. 

Unexplainable: Phages | 4/28

Phages are the most abundant biological entities on Earth (for every grain of sand in the world, there are a trillion phages), and we barely know anything about them. They contain 2 billion pieces of genetic code that exist nowhere else on Earth, and they kill half the world’s bacteria every 48 hours. Cracking their code could be critical to understand our biological ecosystem, but even more tantalizingly, phages may be the answer to a host of currently incurable diseases. By 2050, 10 million people are projected to die each year from antibiotic-resistant infections, and phages could be our last hope.

The natural world

Vox Quick Hits: What’s the Story? The mushroom boom | 4/19

It feels like mushrooms are everywhere these days, but why? Vox culture reporter Terry Nguyen explains why mushrooms are super versatile, and how the fungi took over food, wellness, and (of course) drugs.

Unexplainable: The Twilight Zone of the ocean | 4/21

Every day, untold numbers of strange organisms rise from the middle of the ocean to its surface. They may be playing a crucial role in slowing climate change, so scientists are struggling to understand this migration … before it’s too late.

Today, Explained: A plan to protect the planet | 4/23

Or at least 30 percent of it.

What to read/watch/buy

Vox Quick Hits: The Best Money I Ever Spent: A kayak that made me appreciate where I come from | 4/8

When Max Ufberg left New York for Pennsylvania at the beginning of March in 2020, he assumed it wouldn’t be for long. But as weeks became months, he found solace exploring the place that he had once been so eager to leave behind.

Vox Quick Hits: What to Watch: Mother! | 4/16

Vox film critic Alissa Wilkinson and critic-at-large Emily VanDerWerff explain why Mother! is perhaps the weirdest environmental movie you’ll ever see. They dig into the plot, the allegory and the ways it can be interpreted.

Vox Quick Hits: Ask a Book Critic:

rden greener | 4/21

Vox book critic Constance Grady recommends books that teach you how to make your home and garden greener.

Vox Quick Hits: The Best Money I Ever Spent: A HEPA filter for my parents | 4/22

After the California Camp Fire in 2018, Grace Linden’s parents did not purchase an air purifier — nor did friends, or friends’ parents, or anyone she knew. But that changed by 2020, after more devastating fires and a year of no control due to the pandemic.

If 2020 teaches us anything, it’s that the next crisis we could have prevented is probably right around the corner, and it will be painful. A pandemic that scientists warned was very likely to occur arrived and has already killed well over 250,000 people in the US. Dozens of predicted, large wildfires — the latest evidence of the climate emergency — recentlu torched the American West, their smoke more damaging to health than almost any fire season on record.  

But it’s not too late to intervene and limit climate chaos.

A June paper in Nature Communications clarifies whose actions in this moment are “central to any future prospect of retreating to safer environmental conditions.” Yes, government and industry leaders are on the hook to decarbonize operations and infrastructure. But it’s also the affluent who use far more resources than the poor — more energy and more material goods per capita than the planet can sustain.

“Highly affluent consumers drive biophysical resource use (a) directly through high consumption, (b) as members of powerful factions of the capitalist class and (c) through driving consumption norms across the population,” the authors write. 

The rich or merely affluent, it turns out, are actually the ones blowing through the world’s carbon budget — the maximum amount of cumulative emissions that can be added to the atmosphere to hit the Paris agreement’s 1.5 degrees Celsius of warming goal.

According to a September report from Oxfam and the Stockholm Environment Institute, the richest 10 percent of the world’s population — those who earned $38,000 per year or more as of 2015 — were responsible for 52 percent of cumulative carbon emissions and ate up 31 percent of the world’s carbon budget from 1990 to 2015.

Meanwhile, the richest 1 percent of people — who made $109,000 or more per year in 2015 — alone were responsible for 15 percent of cumulative emissions, and used 9 percent of the carbon budget.

The rapidly accelerating growth in total emissions worldwide isn’t mainly about an improvement in quality of life for the poorer half of the world’s population, either. Instead, the report finds, “nearly half the growth has merely allowed the already wealthy top 10 percent to augment their consumption and enlarge their carbon footprints.” Another recent study found that affluent frequent fliers who make up just 1 percent of the global population are responsible for 50 percent of carbon dioxide emissions from commercial aviation.

In sum, as Tim Gore, head of climate policy at Oxfam, said in a statement, “The over-consumption of a wealthy minority is fueling the climate crisis yet it is poor communities and young people who are paying the price.”

Somehow, in all the campaigns to inspire climate action, the onus on well-off people to take the lead on sustainable consumption has been lost. But the Covid-19 pandemic may turn out to be the best opportunity — especially for the affluent among us — to shift consumption habits.

Here’s why: When we cut back on energy-intensive travel and shopping in the spring, it was easier to see the mindlessness, and even lack of satisfaction, in these patterns. For some people, “the Covid-19 crisis has shown that maybe we can do things differently, that a simpler life can be more fulfilling and provide more happiness,” says Tommy Wiedmann, a professor of sustainability research at UNSW Sydney and a co-author of the Nature Communications paper.

Permanently reducing air travel, driving, home energy use, food waste, and shopping to protect our kids and grandkids from climate chaos need not lead to any reduction in quality of life. In fact, it may even go a long way toward improving it (for ourselves and others). As Vox’s Sigal Samuel reported in June, the top change readers she surveyed said they wanted to maintain after quarantine was “reducing consumerism.” “A long period of being shut in and not spending as much has led to the realization that so much of our consumer behavior is about instant gratification, not lasting happiness,” she writes.

We can also use lessons from our new Covid-constrained life for further economic reforms tailored to the climate emergency reality we find ourselves in. As Pope Francis put it in a Saturday speech on climate change, “The current economic system is unsustainable. We are faced with a moral imperative … to rethink many things,” including means of production, consumerism, waste, indifference to the poor, and harmful energy sources, according to Reuters.

In particular, degrowth is a promising framework for meeting basic needs and improving well-being while staying within the carbon budget and planetary boundaries.

While individual contributions to climate change may be dwarfed by the contributions of fossil fuel companies and heavy industry, individual changes can also spread by “behavioral contagion,” social tipping points, and positive feedback loops.

Here we’ll lay out some of the key opportunities for fellow fortunates who have the economic freedom to choose how and what they consume. Individual, grassroots changes are essential to a bigger systemic change; personal growth and flourishing can happen through resource degrowth.

Yes, individual choices matter, especially if you’re affluent

From a global perspective, middle-class Americans are in the top 10 percent income-wise. “A $59,000 income in the United States has enough buying power to put you in the 91st percentile globally for per-person income,” according to the Washington Post. And beyond that, our fellow fortunates all have “optional consumption” that we engage in, often unreflectively.

Given that leverage, every energy reduction we can make is a gift to future humans, and all life on Earth. And we should be on guard for excuses to avoid changing individual consumption behaviors; they’re often based on logical, arithmetic, and moral errors.

For instance, affluent people sometimes argue that their consumption choices don’t matter because they’re just one person on a planet of more than 7 billion. But consider the physics of tipping points using an analogy from a 2019 piece we wrote, “12 excuses for climate inaction and how to refute,” which helps explain why our decisions today are so much more critical than they were a decade ago — or even this time last year. 

A useful image here is a pile of sand on one side of a weighing scale; at or near the tipping point, it’s easy to see that every tiny grain of sand contributes to when that side of the scale ultimately falls. Your seemingly tiny contribution — the optional flight, the round-the-clock air conditioning, the thrice-weekly portion of beef — can, arithmetically, add up to make a critical difference. And “the bigger your carbon footprint, the bigger your moral duty,” Greta Thunberg said in her widely cited 2019 speech at the World Economic Forum in Davos, Switzerland.

Where the weighing scale image fails is that there isn’t just one tipping point or one single outcome, but rather a spectrum. The fewer greenhouse gases we emit, the nearer to the safer end of the spectrum we can stay, and the less climate chaos we will create. 

We usually have options where we can choose to have more or less climate impact. Every time we choose more and not less, we’re imposing compounding burdens on others and on our descendants. Our choices will determine whether the future is “merely grim, rather than apocalyptic,” as New York’s David Wallace-Wells writes in his book The Uninhabitable Earth.

Restrained consumption is also a way to prevent the deepening of racial and economic injustice and inequality — low-income people and people of color are among the first to lose the most in climate disasters. Working toward justice means being a resource-responsible consumer. 

“I think it is important for people to say that they will not do certain types of consumption anymore,” Julia Steinberger, a professor of ecological economics at the University of Leeds and a co-author of the Nature Communications paper, tells Vox. “It’s about making this way of life more visibly unacceptable. The rich could show their status and prestige with other things than lots of cars and huge houses and lots of material wealth.”

With all this in mind, here are five potential resource-responsible actions to commit to, in no particular order:

1. Drive and fly less, since the top 10 percent uses around 45 percent of land transport energy and 75 percent of air transport energy, per a 2020 paper by Steinberger in Nature Energy.
2. Retrofit your house and purchase clean energy, since roughly 20 percent of US energy-related greenhouse gas emissions come from heating, cooling, and powering households.
3. Buy food mindfully (less meat and dairy, don’t waste what you buy), since meat and dairy account for around 14.5 percent of global greenhouse gas emissions, according to the UN’s Food and Agricultural Organization.
4. Shop less, since the fashion industry generates at least 5 percent of global emissions.
5. Ditch status-signaling SUVs, since SUVs were the second-largest source of the global rise in emissions over the past decade, eclipsing all shipping, aviation, heavy industry, and even trucks.

The pleasures of much of our consumption are fast forgotten, but the costs are slow and will be felt by generations for centuries to come

Despite what consumption enthusiasts and their enablers (marketers, economists, etc.) preach, the benefits and pleasures of much of our consumption are fleeting. Many of us have an inkling of this from our own experience, but we’re trapped on the treadmill of unthinking hedonic habits. 

That enduring lack of true satisfaction is confirmed by much ancient wisdom: Enlightenment, or Nirvana, is the “ the absence of greed, absence of dislike, and absence of egoism,” as the Buddhist writer and scholar Stephen Batchelor notes in an interview with On Being’s Krista Tippett. And one of the most robust findings in social science, according to economist Robert Frank at Cornell, is the research on how emotional well-being doesn’t improve above an annual (individual) income of $75,000.

Some of our least effective consumption occurs in the form of self-soothing habits. When we’re feeling bad, or anxious, or bored, we often seek relief in impulsive shopping, a.k.a. retail therapy. 

What longer-lasting reliefs beat fleeting fun? You may have experienced part of the answer in these Covid-constrained conditions. For many, an activity as simple as a walk has been their day’s treat. 

That’s especially true if you find beauty or curiosity on your walk, where you notice things interesting enough to achieve what Iris Murdoch called “unselfing” — taking you out of your self-centered anxieties, even if only temporarily. (Here’s some background on this idea from Maria Popova.)  

These spirit-supporting pleasures typically take more effort than reaching for “junk” treats (like a quick online purchase). But, in addition to being more satisfying, they often lack negative knock-on effects, like putting more carbon into the atmosphere. This carbon cost isn’t just about you — it is our collective legacy to our children and all future humans. 

Hopefully, Covid-19 can teach us to pay attention to planetary boundaries and other collective threats we’ve long ignored. On climate, we should wake up to the intergenerational zero-sum game we are playing, where the carbon-generating and resource-depleting consumption we indulge in now compromises the safety of future humans.

Every physical resource is limited, or is renewable within certain limits. And this logic means there is no “green growth” solution here unless we reduce consumption: the approach known as “degrowth.”

Degrowth, explained

Even before Covid-19, a fundamental restructuring of the economy was very clearly needed to right the gaping inequities, the shockingly lopsided accumulation — nay, hoarding — of wealth. The factors that led to that are only being exacerbated by Covid-19. But as we recover from the pandemic, richer countries and citizens have a tremendous opportunity to remold under another paradigm. 

Degrowth, as the economic anthropologist Jason Hickel puts it, is about rich countries “actively scaling down resource use and energy use.”

On a recent episode of the Freakonomics podcast, he clarified: “When people hear ‘degrowth,’ they think that sounds like a recession. But here’s the thing … a recession is what happens when a growth-oriented economy stops growing. It’s a disaster. People lose their jobs. They lose their houses. Poverty rates rise, etc. ‘Degrowth’ is calling for a shift to a fundamentally different kind of economy altogether.”

As Wiedmann, Steinberger, and their co-authors describe it, degrowth is a “downscaled steady-state economic system that is socially just and in balance with ecological limits.”

Taking advantage of this opportunity also requires going beyond a focus on carbon emissions. Clean energy, for example, won’t deliver a sustainable economy by itself. It’s about our resource use more broadly. (Even preexisting sweeping proposals like the Green New Deal often don’t address material limits.)

As Hickel wrote in June in Foreign Policy:

Ecologists say that the planet can handle maximum annual resource use of about 50 billion metric tons per year. We crossed that planetary boundary in the late 1990s, and today we’re overshooting it by more than 90 percent. This is what’s driving ecological breakdown: Every additional ton of material extraction has an impact on the planet’s ecosystems. 

The outer limit works out to be about 6 metric tons per human per year. The current US average is 35 metric tons, with those toward the top of the income scale consuming vastly more. This means there is no avoiding the urgent need for deep cuts in energy and material use in rich nations, especially among those countries’ richest citizens. 

Since we may not be able to remove much of the carbon that has already been emitted, or return the materials that have already been extracted, it’s best now to adopt a forward-looking redemption stance. What matters most is reducing impacts from here on out, rather than prosecuting past “sins,” often committed unwittingly, or by rich-mimicking rather than explicit choice. And that means choosing not to mindlessly add more grains of sand to the scale.

There are green shoots visible of the vast changes needed. China committed Tuesday to achieve carbon neutrality by 2060 and peak its emissions by 2030. Night trains are coming back in Europe partially in response to people demanding low-carbon alternatives to flying. A group of European central bankers wrote in the Guardian in June that “the pandemic offers a unique chance to green the global economy” and is mobilizing businesses, investors, banks, and governments “to ensure climate risks are effectively managed in the financial system.” 

You, too, can bank on bettering your personal economy by creating a new normal of mindful consumption and making it visible to others in the affluent class, as Steinberger advises. You’ll be a better, and probably happier, person. And other humans, including your kids, will thank you. 

Researchers at the University of Nevada have reported that a 25-year-old man was reinfected in June with SARS-CoV-2, the virus the causes Covid-19. He joins a handful of other confirmed cases of reinfection in people without immune disorders — in Belgium, the Netherlands, Hong Kong, and Ecuador — where researchers have demonstrated that the genetic signature of the second infection did not match that of the first.

According to a new study on the Nevada case, published in The Lancet Infectious Diseases journal, the patient first tested positive in April, and then tested negative for the virus twice. In June, 48 days later, “the patient was hospitalized and tested positive for a second time,” according to the authors, and he experienced severe symptoms. There were major genetic differences between the two infections, suggesting that the patient got the virus twice. (Since then, the patient has recovered.)

The report is in line with what immunity experts have been telling us is possible with this virus: that reinfection is possible and, to some extent, expected, with a coronavirus. But it also shows us how much we still have to learn: about how much protection a single infection can confer, about what exactly a robust long-duration immune response looks like, and about what determines the severity of disease in a second infection.

“Does immunity protect an individual from disease on reinfection?” writes Yale immunobiology researcher Akiko Iwasaki in an accompanying editorial in The Lancet Infectious Diseases. “The answer is not necessarily, because patients from Nevada and Ecuador had worse disease outcomes at reinfection than at first infection.”

The Nevada case is an important finding, since in the two other confirmed cases of reinfection, the patients had mild disease or were asymptomatic. Scientists still don’t know how common reinfection is (it may well be very rare), nor can they determine an individual’s chances of getting infected again.

They do know there are many, many components of our immune system that work together to fight the coronavirus, and immunity doesn’t mean one single thing. And while we’re waiting for scientists to figure it all out, everyone, including those who’ve already had the virus, should still try to avoid getting infected at all.

The new study “strongly suggests that individuals who have tested positive for SARS-CoV-2 should continue to take serious precautions when it comes to the virus, including social distancing, wearing face masks, and handwashing,” said Mark Pandori, of the Nevada State Public Health Laboratory at the University of Nevada Reno School of Medicine and lead author of the study, in a statement.

Let’s walk through the basics of immunity, and what we’re learning about reinfection.

There are no simple stories about immunity and Covid-19

The immune system is profoundly complicated, and “immunity” can mean many different things. A lot of this nuance gets lost in headlines about immunity.

For instance: Previous research has shown that neutralizing antibodies — immune system proteins that latch onto pathogens and prevent them from infecting cells — can wane in the months after a Covid-19 infection, particularly when the initial infection was mild. Some wondered if that meant the end of herd immunity hopes.

In the Nevada case, we know that “the patient had positive antibodies after the reinfection, but whether he had pre-existing antibody after the first infection is unknown,” writes Iwasaki.

But what’s often misunderstood is that antibodies are only one component of the immune system, and losing them does not leave a person completely vulnerable to the virus.

In fact, there are several parts of the immune system that may contribute to lasting protection against SARS-CoV-2.

One is killer T-cells. “Their names give you a good hint what they do,” Alessandro Sette, an immunologist at the La Jolla Institute for Immunology, told me in July. “They see and destroy and kill infected cells.”

Antibodies, he explained, can clear virus from bodily fluids. “But if the virus gets inside the cell, then it becomes invisible to the antibody.” That’s where killer T-cells come in: They find and destroy these hidden viruses.

While antibodies can prevent an infection, killer T-cells deal with an infection that’s already underway. So they play a huge role in long-term immunity, stopping infections before they have time to get a person very sick.

And it’s not just killer T-cells and antibodies. There are also helper T-cells, which facilitate a robust antibody cell response. “They are required for the antibody response to mature,” Sette says.

Some proportion of the population (perhaps 25 to 50 percent of people) seems to have some preexisting T-cells (of both varieties, but the helper kind have been more commonly observed) that respond to SARS-CoV-2, despite these people never having been exposed to SARS-CoV-2. The hypothesis is that these people may have acquired these T-cells from being infected with other strains in the coronavirus family of viruses. Researchers still don’t really understand what role these preexisting T-cells play in preventing or attenuating infection (if any).

But wait, there’s more! There’s another group of cells called memory B-cells. B-cells are the immune system cells that create antibodies. Certain types of B-cells become memory B-cells. These save the instructions for producing a particular antibody, but they aren’t active. Instead, they hide out — in your spleen, in your lymph nodes, perhaps at the original site of your infection — waiting for a signal to start producing antibodies again.

All the things “immunity” can mean

All these different components of the immune system mean “immunity” isn’t just one thing.

Immunity could mean a strong antibody response, which prevents the virus from establishing itself in cells. But it could also mean a good killer T-cell response, which could potentially stop an infection very quickly: before you feel sick and before you start spreading the virus to others.

“In many infections, the virus does reproduce a little bit, but then the immune response stops this infection in its tracks,” Sette explains. Also possible: “You do get infected, you do get sick, but your immune system does enough of a job curbing the infection, so you don’t get as sick.”

Immunity might also result from an awakening of memory B-cells. If an individual has memory B-cells and is exposed to the virus again, “that infection will stimulate a much faster antibody response to the virus, which would, theoretically lead to faster clearance of the virus and potentially less severe infection,” Elitza Theel, the director of the infectious diseases serology laboratory at the Mayo Clinic, said in a July interview.

In general, scientists believe, the stronger the infection (and immune response) that occurs during an initial infection, the longer immunity will last.

So reinfection may still be possible, but it may not mean severe illness. When a virus invades a body, generally, the body remembers.

Could asymptomatic infections spread the virus? Unclear.

It’s still not known what the latest reinfection study means for how long the pandemic will last. If reinfections happen regularly (and we have no idea how common they might be), then it might take longer to achieve herd immunity without a vaccination (which is an un-ideal, and cynical, goal to begin with). How long immunity lasts, on average, and how common reinfection is are key unknown variables in figuring out how long the pandemic may last in the absence of an effective vaccine or treatment.

“Reinfection cases tell us that we cannot rely on immunity acquired by natural infection to confer herd immunity; not only is this strategy lethal for many but also it is not effective,” Iwasaki wrote in the editorial. “Herd immunity requires safe and effective vaccines and robust vaccination implementation.”

We also have much more to learn about how often reinfections lead to more clusters of cases. Recently, I asked Shane Crotty, an immunologist at the La Jolla Institute for Immunology, about this very scenario.

“Could there be an ‘immunity’ scenario,” I asked, “where, after having recovered from Covid, a person could get infected again but not feel sick at all, and also be able to spread it?”

“It is a good question, and the answer is that no one knows,” Crotty replied. “There are cases with other diseases where asymptomatic immune people can be infectious. There is definitely a lot to learn still about immunity to SARS-CoV-2.”