FDA authorizes Pfizer coronavirus vaccine for adolescents 12 to 15 years old

https://www.washingtonpost.com/health/2021/05/10/coronavirus-vaccine-for-kids/?fbclid=IwAR0RKJNrlP3TiTDrvPuczKSHIPmTRds8kdAepwOCSqlrzdDHgGcm9vlBYk8

FDA authorizes Pfizer COVID-19 vaccine in adolescents 12 and up

The Food and Drug Administration cleared the first coronavirus vaccine for emergency use in children as young as 12 on Monday, expanding access to the Pfizer-BioNTech shot to adolescents ahead of the next school year and marking another milestone in the nation’s battle with the virus.

The decision that the two-shot regimen is safe and effective for younger adolescents had been highly anticipated by many parents and pediatricians, particularly with the growing gap between what vaccinated and unvaccinated people may do safely. Evidence suggests that schools can function at low risk with prevention measures, such as masks and social distancing. But vaccines are poised to increase confidence in resuming in-person activities and are regarded as pivotal to returning to normalcy.

“Adolescents, especially, have suffered tremendously from the covid pandemic. Even though they’re less likely than adults to be hospitalized or have severe illness, their lives really have been curtailed in many parts of the country,” said Kawsar R. Talaat, an assistant professor of international health at the Johns Hopkins Bloomberg School of Public Health. “A vaccine gives them an extra layer of protection and allows them to go back to being kids.”

Expert advisers to the Centers for Disease Control and Prevention are scheduled to meet Wednesday to recommend how the vaccine should be used in that age group, and the vaccine can be administered as soon as the CDC director signs off on the recommendation.

In a news briefing Monday evening after the announcement, FDA officials said the Pfizer authorization for 12- to 15-year-olds was a straightforward decision because the data showed that the vaccine was safe and that the response to the vaccine was even better than among the 18- to 25-year-olds who got the shots.

Children rarely suffer serious bouts of covid-19, the illness caused by the coronavirus. But there is no way to predict the few who will become dangerously sick or develop a rare, dangerous inflammatory syndrome. Out of more than 581,000 covid-19 deaths in the United States, about 300 have been people under 18 — a tiny fraction of the total. But that exceeds the number of children who die in a bad flu season.

Children appear to be less efficient at spreading the virus, although their role in transmission is still not fully understood — another reason for pediatric vaccinations.

Clinicians also worry that with a new virus with many unknowns, the possibility exists for long-term impacts of infection, even from the mild or asymptomatic courses of illness common among children.

The Pfizer-BioNTech vaccine, already authorized for adolescents 16 and older, was the first to be tested in younger adolescents. The FDA’s decision will provide a potential path for other vaccine-makers to follow, most of which have launched or plan to initiate trials of their vaccines in teenagers and younger children.

The agency based its authorization on a trial of nearly 2,300 adolescents between 12 and 15 years old, half of whom received the same two-shot regimen shown effective and safe in adults. Researchers took blood samples and measured antibody levels triggered by the shots and foundstronger immune responses in the teens than those found in young adults. There were 16 cases of covid-19 in the trial, all of them among adolescents who received a placebo, suggesting the regimen offered similar protection to younger recipients as it does to adults.

Robert W. Frenck Jr., the researcher who led the adolescent trial at Cincinnati Children’s Hospital Medical Center, said the study was designed to test whether it triggered immune responses, not whether it prevented disease. But because of the number of children who became ill in the placebo arm of the trial, it also became evident the vaccine offered robust protection.

“That really points out how much covid there is in the adolescent community,” Frenck said.

The data has not been published or peer-reviewed, but Kathryn M. Edwards, a pediatric infectious-disease specialist at Vanderbilt University Medical Center, said the results announced by Pfizer were “pretty exciting — it looked very effective and the immune responses were really good.”

Edwards said she is comfortable the benefits of vaccinations are clear among teens, noting that while children, in general, are at lower risk of severe covid-19 than adults, older adolescents seem to be more like adults in their risk for covid-19 than the very youngest children.

Audrey Baker, 15, and Sam Baker, 12, rolled up their sleeves for shots in the Pfizer-BioNTech trial at Cincinnati Children’s Hospital Medical Center. Audrey said she had no hesitation about signing up, and misses little things about how life used to be — eating out in restaurants and seeing family.

“I just trusted the science,” Audrey said. “I knew it was tested in adults. I was really just joining, hoping that maybe I could get vaccinated and help out science.”

Sam said he was more hesitant, in part because participating meant many follow-up lab tests. But he decided to do it and thinks he may have gotten the vaccine in the trial because he developed a headache and fever after his second dose.

Their mother, Rachel Baker, said she felt relief because of Sam’s symptoms.

The biggest benefit has been that I feel a weight off my shoulders,” Rachel said. “We haven’t changed how we do anything. … We’re still masking, we’re still social distancing, but we’re a bit calmer about it all.”

H. Cody Meissner, a pediatrician at Tufts Medical Center and a member of an external advisory committee to the FDA, said he thinks a pediatric vaccine is needed. But he said he would like to see more safety data because the messenger RNA technology at the core of vaccines from Pfizer-BioNTech and the biotechnology company Moderna does not have a long, established safety record, and its first large-scale use began in December.

Meissner abstained from the December vote that overwhelmingly recommended authorization of the Pfizer-BioNTech vaccine for people 16 and older, because he thought the vaccine should be authorized in people 18 and older.

“For those who are eager to get it, it’s important for them to understand that this is very rarely a severe disease in young adolescents, number one, and this is an entirely new vaccine,” Meissner said. “I just don’t want people to get too swept up in fear of hospitalization and death from covid-19 for the first few decades of life.”

But many other physicians take comfort knowing that 250 million shots of messenger RNA vaccine have been given in the United States alone. Serious side effects, such as a risk of anaphylaxis, are extremely rare. Because the trial in teens was an “immune bridging” trial designed to test whether the vaccine triggered immune responses similar to those in adults, researchers did not need to recruit tens of thousands of people to see if those who received a vaccine were protected against illness. The immune bridging technique is commonly used to expand access to vaccines that have been proved effective and safe to adolescents or other populations.

The expansion of eligibility to children will probably ignite debates in families about when to get vaccinated, and among policymakers about whether it should be required.

Dorit Reiss, a law professor focused on vaccine policy at the University of California Hastings College of Law, said she thinks it is unlikely children will be mandated to receive a coronavirus shot until the vaccines win full approval and not just emergency use authorization.

She predicted that acceptance of the vaccine will evolve as more children are vaccinated and depend on the state of the pandemic. She noted that when vaccines are introduced, the rollout often starts slowly before accelerating.

“Nervousness about a new vaccine is normal, especially when it’s for kids,” Reiss said. “Parents that are nervous now might feel different in a few months, once their friends’ kids have gotten vaccinated. And the views of the kids are also going to matter — if teens are going to think this is going to make their lives easier.”

Opening up vaccinations to children may sharpen a debate unfolding globally about the equity of vaccine access. Talaat said that while she can’t wait for her kids to have access to a vaccine, she is troubled by the global inequities as high-risk front-line workers or older people still don’t have access to vaccines in countries where the coronavirus is out of control.

Moderna announced Thursday that an initial analysis of its teen trial found its vaccine was 96 percent effective among participants who received at least one dose. Moderna is in discussions with regulators about the data. Pfizer-BioNTech and Moderna are testing their vaccines in children as young as infants. Johnson & Johnson is planning pediatric trials of its single-shot vaccine.

Trials in younger children are expected to take longer, because researchers must step down gradually in age and determine a safe and effective dose. William Gruber, senior vice president of vaccine clinical research and development at Pfizer, said data from tests in children as young as 2 years old may be available by September or October, with data on children as young as 6 months possible by the end of the year.

Within each age category, a separate risk-benefit assessment may take place. In the youngest children, given the low risk from the coronavirus, side effects may figure more prominently into the analysis, for example. Researchers may end up choosing a lower dose of vaccine. The understanding of children’s role in transmission may also evolve and help guide vaccine use and public policy.

“We are proceeding carefully, cautiously,” Edwards said. “We’re using the same rigid guidelines we use in all vaccines, and we take this very seriously. I think as time goes on and more information becomes available, some of the questions may be easier to address.”

Cartoon – Never Reaching Herd Immunity

Herd immunity hard to achieve if you've heard wrong info

Cartoon – Reaching Herd Immunity

Cartoon: Herd Immunity | Columnists | tulsaworld.com

Reaching ‘Herd Immunity’ Is Unlikely in the U.S., Experts Now Believe

Reaching 'Herd Immunity' Is Unlikely in the U.S., Experts Now Believe - The  New York Times

Widely circulating coronavirus variants and persistent hesitancy about vaccines will keep the goal out of reach. The virus is here to stay, but vaccinating the most vulnerable may be enough to restore normalcy.

Early in the pandemic, when vaccines for the coronavirus were still just a glimmer on the horizon, the term “herd immunity” came to signify the endgame: the point when enough Americans would be protected from the virus so we could be rid of the pathogen and reclaim our lives.

Now, more than half of adults in the United States have been inoculated with at least one dose of a vaccine. But daily vaccination rates are slipping, and there is widespread consensus among scientists and public health experts that the herd immunity threshold is not attainable — at least not in the foreseeable future, and perhaps not ever.

Instead, they are coming to the conclusion that rather than making a long-promised exit, the virus will most likely become a manageable threat that will continue to circulate in the United States for years to come, still causing hospitalizations and deaths but in much smaller numbers.

How much smaller is uncertain and depends in part on how much of the nation, and the world, becomes vaccinated and how the coronavirus evolves. It is already clear, however, that the virus is changing too quickly, new variants are spreading too easily and vaccination is proceeding too slowly for herd immunity to be within reach anytime soon.

Continued immunizations, especially for people at highest risk because of age, exposure or health status, will be crucial to limiting the severity of outbreaks, if not their frequency, experts believe.

“The virus is unlikely to go away,” said Rustom Antia, an evolutionary biologist at Emory University in Atlanta. “But we want to do all we can to check that it’s likely to become a mild infection.”

The shift in outlook presents a new challenge for public health authorities. The drive for herd immunity — by the summer, some experts once thought possible — captured the imagination of large segments of the public. To say the goal will not be attained adds another “why bother” to the list of reasons that vaccine skeptics use to avoid being inoculated.

Yet vaccinations remain the key to transforming the virus into a controllable threat, experts said.

Dr. Anthony S. Fauci, the Biden administration’s top adviser on Covid-19, acknowledged the shift in experts’ thinking.

“People were getting confused and thinking you’re never going to get the infections down until you reach this mystical level of herd immunity, whatever that number is,” he said.

“That’s why we stopped using herd immunity in the classic sense,” he added. “I’m saying: Forget that for a second. You vaccinate enough people, the infections are going to go down.”

Why reaching the threshold is tough

Once the novel coronavirus began to spread across the globe in early 2020, it became increasingly clear that the only way out of the pandemic would be for so many people to gain immunity — whether through natural infection or vaccination — that the virus would run out of people to infect. The concept of reaching herd immunity became the implicit goal in many countries, including the United States.

Early on, the target herd immunity threshold was estimated to be about 60 to 70 percent of the population. Most experts, including Dr. Fauci, expected that the United States would be able to reach it once vaccines were available.

But as vaccines were developed and distribution ramped up through the winter and into the spring, estimates of the threshold began to rise. That is because the initial calculations were based on the contagiousness of the original version of the virus. The predominant variant now circulating in the United States, called B.1.1.7 and first identified in Britain, is about 60 percent more transmissible.

As a result, experts now calculate the herd immunity threshold to be at least 80 percent. If even more contagious variants develop, or if scientists find that immunized people can still transmit the virus, the calculation will have to be revised upward again.

Polls show that about 30 percent of the U.S. population is still reluctant to be vaccinated. That number is expected to improve but probably not enough. “It is theoretically possible that we could get to about 90 percent vaccination coverage, but not super likely, I would say,” said Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health.

Though resistance to the vaccines is a main reason the United States is unlikely to reach herd immunity, it is not the only one.

Herd immunity is often described as a national target. But that is a hazy concept in a country this large.

“Disease transmission is local,” Dr. Lipsitch noted.

“If the coverage is 95 percent in the United States as a whole, but 70 percent in some small town, the virus doesn’t care,” he explained. “It will make its way around the small town.”

Uneven Willingness to Get Vaccinated Could Affect Herd Immunity

In some parts of the United States, inoculation rates may not reach the threshold needed to prevent the coronavirus from spreading easily.

How insulated a particular region is from the coronavirus depends on a dizzying array of factors.

Herd immunity can fluctuate with “population crowding, human behavior, sanitation and all sorts of other things,” said Dr. David M. Morens, a virologist and senior adviser to Dr. Fauci. “The herd immunity for a wealthy neighborhood might be X, then you go into a crowded neighborhood one block away and it’s 10X.”

Given the degree of movement among regions, a small virus wave in a region with a low vaccination level can easily spill over into an area where a majority of the population is protected.

At the same time, the connectivity between countries, particularly as travel restrictions ease, emphasizes the urgency of protecting not just Americans but everyone in the world, said Natalie E. Dean, a biostatistician at the University of Florida in Gainesville. Any variants that arise in the world will eventually reach the United States, she noted.

Many parts of the world lag far behind the United States on vaccinations. Less than 2 percent of the people in India have been fully vaccinated, for example, and less than 1 percent in South Africaaccording to data compiled by The New York Times.

“We will not achieve herd immunity as a country or a state or even as a city until we have enough immunity in the population as a whole,” said Lauren Ancel Meyers, the director of the Covid-19 Modeling Consortium at the University of Texas at Austin.

If the herd immunity threshold is not attainable, what matters most is the rate of hospitalizations and deaths after pandemic restrictions are relaxed, experts believe.

By focusing on vaccinating the most vulnerable, the United States has already brought those numbers down sharply. If the vaccination levels of that group continue to rise, the expectation is that over time the coronavirus may become seasonal, like the flu, and affect mostly the young and healthy.

“What we want to do at the very least is get to a point where we have just really sporadic little flare-ups,” said Carl Bergstrom, an evolutionary biologist at the University of Washington in Seattle. “That would be a very sensible target in this country where we have an excellent vaccine and the ability to deliver it.”

Over the long term — a generation or two — the goal is to transition the new coronavirus to become more like its cousins that cause common colds. That would mean the first infection is early in childhood, and subsequent infections are mild because of partial protection, even if immunity wanes.

Some unknown proportion of people with mild cases may go on to experience debilitating symptoms for weeks or months — a syndrome called “long Covid” — but they are unlikely to overwhelm the health care system.

“The vast majority of the mortality and of the stress on the health care system comes from people with a few particular conditions, and especially people who are over 60,” Dr. Lipsitch said. “If we can protect those people against severe illness and death, then we will have turned Covid from a society disrupter to a regular infectious disease.”

If communities maintain vigilant testing and tracking, it may be possible to bring the number of new cases so low that health officials can identify any new introduction of the virus and immediately stifle a potential outbreak, said Bary Pradelski, an economist at the National Center for Scientific Research in Grenoble, France. He and his colleagues described this strategy in a paper published on Thursday in the scientific journal The Lancet.

“Eradication is, I think, impossible at this stage,” Dr. Pradelski said. “But you want local elimination.”

The endpoint has changed, but the most pressing challenge remains the same: persuading as many people as possible to get the shot.

Reaching a high level of immunity in the population “is not like winning a race,” Dr. Lipsitch said. “You have to then feed it. You have to keep vaccinating to stay above that threshold.”

Skepticism about the vaccines among many Americans and lack of access in some groups — homeless populations, migrant workers or some communities of color — make it a challenge to achieve that goal. Vaccine mandates would only make that stance worse, some experts believe.

A better approach would be for a trusted figure to address the root cause of the hesitancy — fear, mistrust, misconceptions, ease of access or a desire for more information, said Mary Politi, an expert in health decision making and health communication at Washington University in St. Louis.

People often need to see others in their social circle embracing something before they are willing to try it, Dr. Politi said. Emphasizing the benefits of vaccination to their lives, like seeing a family member or sending their children to school, might be more motivating than the nebulous idea of herd immunity.

“That would resonate with people more than this somewhat elusive concept that experts are still trying to figure out,” she added.

Though children spread the virus less efficiently than adults do, the experts all agreed that vaccinating children would also be important for keeping the number of Covid cases low. In the long term, the public health system will also need to account for babies, and for children and adults who age into a group with higher risk.

Unnerving scenarios remain on the path to this long-term vision.

Over time, if not enough people are protected, highly contagious variants may develop that can break through vaccine protection, land people in the hospital and put them at risk of death.

“That’s the nightmare scenario,” said Jeffrey Shaman, an epidemiologist at Columbia University.

How frequent and how severe those breakthrough infections are have the potential to determine whether the United States can keep hospitalizations and deaths low or if the country will find itself in a “mad scramble” every couple of years, he said.

“I think we’re going to be looking over our shoulders — or at least public health officials and infectious disease epidemiologists are going to be looking over their shoulders going: ‘All right, the variants out there — what are they doing? What are they capable of?” he said. “Maybe the general public can go back to not worrying about it so much, but we will have to.”

More than a year into the pandemic, we’re still figuring out what risks we’re willing to take

Charting the pandemic over the next 12 months — and beyond - STAT

When the Centers for Disease Control and Prevention last week issued guidelines for what vaccinated people can safely do, the agency employed the word “risk” 43 times.

The word often carried a modifier, like so: increased risk, residual risk, low risk, potential risk, minimal risk, higher risk. The CDC did not define “low,” “minimal” or “higher,” instead using broad brushstrokes to paint a picture of post-vaccination life.

For example: “Indoor visits or small gatherings likely represent minimal risk to fully vaccinated people.”

On Wednesday, CDC director Rochelle Walensky said she could not give a definitive answer to what a “small” gathering is, because there are too many variables.

“If we define a small- and medium-sized gathering, we actually also have to define the size of the space that it’s in, the ventilation that is occurring, the space between people. And so, I think we should get back to the the general concepts,” Walensky said.

The situation has left people where they’ve been since the start of the pandemic: forced to play the role of amateur epidemiologist.

In the early days of the pandemic, we wondered if we could catch the coronavirus from a passing jogger and if our groceries, fresh from the store and resting on the kitchen counter, threatened to kill us. Science has attenuated some of our earliest fears. But more than a year into this crisis, we’re still trying to perform complicated risk calculations while relying on contradictory research and shifting CDC guidance.

Risk analysis is not something humans are necessarily good at. We rely on anecdotes more than scientific data. The questions we ask rarely have a simple yes or no answer. Risk tends to be on a sliding scale. Outside of self-isolation, there is no obvious way to drive the risk of viral transmission to zero, nor is risky behavior guaranteed to result in a dire outcome. We have no choice but to live probabilistically.

The risk landscape keeps changing as well. The virus is mutating, and there are many different variants in circulation. Many people are now fully vaccinated, some only partially vaccinated (in between shots, for example), some unvaccinated and some armored with a level of immunity through natural infection. Add the extreme variation in disease severity because of age and underlying conditions, and the risk equations get so long we may run out of chalkboard.

The restrictions imposed by governments have sometimes made little sense. Casinos were open before schools in some states. Mask mandates outdoors remained in place even when indoor dining became permitted.

“It seems to me if we are going to have indoor dining, we should have mask-free jogging,” Harvard epidemiologist Marc Lipsitch said in an email.

One thing that is incontrovertibly true: The coronavirus vaccines are remarkably safe and effective, and people should get vaccinated if possible.

“These are off-the-scale good,” said Amesh Adalja, an infectious-disease doctor and senior scholar at the Johns Hopkins Center for Health Security. “These are much better than vaccines that we rely on every year, like the flu vaccine.”

Even for people sold on vaccines, there remain lingering questions about what is and isn’t safe, and what is and isn’t the proper way to go about daily life in an increasingly vaccinated society. Here, we present some answers, with the caveat that our knowledge of the coronavirus, SARS-CoV-2, is still evolving, as is the virus itself.

Q: Why do I still need to wear a mask after I’m fully vaccinated?

A: You don’t need to wear a mask outdoors when fully vaccinated, except in crowds (such as at a sports stadium or a concert), nor do you have to wear one indoors among other vaccinated people or members of your own household.

But there are situations where you still need to mask up. You could still get infected with the coronavirus, and although it would most likely be mild or asymptomatic, you could transmit the virus to another person. Again, the odds of that happening are low, and there is encouraging data from Israel that suggests vaccinations dramatically reduce community spread.

But remember: A vaccination campaign is not simply about protecting the vaccinated individual. The goal is to build immunity broadly. Moreover, many communities still require masks in public settings — so it’s the law. It’s also polite — you don’t want to make people guess if you’ve been vaccinated or not. That probably will change when infection rates plummet and vaccinations are far more widespread.

“It is also a show of solidarity that we are still in this together,” said Maria Van Kerkhove, technical lead for the World Health Organization’s covid-19 response. “It’s about you and your community, your family, your friends, your workplace, your loved ones. It’s not just about you.”

At some point, viral transmission will plummet. We’re a long way from that point. As long as the virus is circulating in our communities, we need to use what we can to limit the spread and drive down the infection rate.

“Because [the vaccines] are not perfect, that’s precisely why we are urging people to be cautious,” Surgeon General Vivek H. Murthy said in a recent White House covid-19 task force news briefing. “We have great confidence in vaccines. We understood they are not perfect.”

Q: If you’re vaccinated, are you definitely protected against the coronavirus?

A: You’re very likely protected from symptomatic illness. That’s why Adalja, echoing the consensus, said, “These vaccines are something that will change your life.”

In clinical trials, the Pfizer and Moderna vaccines were about 95 percent effective in blocking symptomatic illness after two shots. The one-shot Johnson & Johnson vaccine was not quite as effective but just as good at preventing severe illness and death — which is the highest public health priority in a pandemic like this.

Q: But aren’t there also breakthrough infections?

A: As of April 26, the CDC had documented 9,245 breakthrough infections among fully vaccinated people. But look at the denominator: Those cases were among more than 95 million people. That’s fewer than 1 in 10,000 people vaccinated. (The agency noted that this is probably an undercount because of lack of testing and surveillance.) Of those rare breakthrough cases known to the CDC, 27 percent were asymptomatic and only 9 percent required hospitalization.

Adalja said people need to focus on probabilities and not anecdotes.

“This is kind of a cognitive bias that people have with many kinds of risk. It’s just like when there’s a shark attack in Australia. How much coverage does that get?” he said.

Q: Should people who got the Johnson & Johnson vaccine worry about blood clots?

A: If you notice unusual and serious side effects, such as severe headaches, contact your doctor. But the risk is extremely low. Federal regulators reauthorized the use of the vaccine after a 10-day pause, having found 15 cases of a serious clotting disorder among the 7 million people who had received the vaccine at that time. By any calculation, the risk of a bad vaccine reaction is much less than the risk of getting a serious case of covid-19.

Paul A. Offit, a pediatrician at Children’s Hospital of Philadelphia who is an expert on vaccination, suggests that the Johnson & Johnson coronavirus vaccine suffers from bad timing. Had it been approved first, before the Pfizer and Moderna vaccines, its many virtues would have been celebrated and the rare side effects minimized.

He noted that the Johnson & Johnson vaccine is “refrigerator stable” for up to five weeks. The vaccine is appealing to public health officials because it’s one-and-done and can be more easily deployed in remote locations and in places where recipients are homebound.

Q: How long will natural or vaccine-induced immunity last?

A: No one knows, but the initial evidence is encouraging, said Alessandro Sette, a professor of immunology at the La Jolla Institute for Immunology. A research paper published by Sette and fellow researchers in January showed that 90 percent of people who recovered from a coronavirus infection had robust levels of immunity eight months after they became sick. Immunity did not suddenly drop after eight months — that was merely the limit of the research period.

“Ninety percent having a good immune response also means 10 percent don’t. That is a reason for vaccinating and being careful even if you had the disease,” Sette said.

Immunity post-vaccination also appears durable, and there is less variability in levels of antibodies and other immune system cells following a vaccination than following a natural infection, Sette said.

Because this is a novel disease, and vaccines have not been widely deployed for very long, it is too soon to know how long antibodies will last. But Sette pointed out that the immune system has other weapons against invasive viruses, including “killer T-cells,” which continue to be able to recognize infected cells and kill them, preventing viral replication.

Q: Do the vaccines work against these new virus variants? And shouldn’t we be worried about a new variant that has even scarier, vaccine-evading mutations?

A: The immune response generated by vaccines is sufficiently protective against coronavirus variants to prevent most people from getting seriously ill.

Infectious-disease experts do worry about future mutations that could allow the virus to exhibit vaccine evasion. That said, there are limits to how much the virus can mutate — how much it can change its structure — and still function, according to Sette.

“The virus has to walk a tightrope,” he said. The virus can mutate to escape the effect of a specific antibody, but “it can’t change too much.”

He added, “While the virus has surprised us this year in a number of ways, the data we’ve seen so far does not suggest there’s an infinite number of ways the virus can mutate and escape immune recognition and still be as infectious.”

Q: When will we reach herd immunity?

A: No one knows what level of immunity would throttle virus transmission, and it probably varies from one environment to another and from one season of the year to another. But in the United States, at least, vaccinations have already had an effect. The virus increasingly is slamming into immune-system walls. Eventually, with enough vaccinations, most of the people who get infected will be dead-end alleys for the virus.

The virus appears destined to pop up in smaller outbreaks that could be more easily contained. But the virus won’t disappear, especially because it continues to spread at catastrophic rates in many countries that have low levels of vaccination. The only infectious disease-causing virus ever eradicated is smallpox.

For now, successful navigation of the pandemic may simply mean taking steps to reduce the threat of a serious case of covid-19 (as best as anyone can determine it) to the level of other threats that we typically tolerate, and which don’t tend to keep us awake at night.