Waiting for a COVID-19 vaccine? Don't get rid of your mask yet.

After nine grueling months of fear, fumbling, devastation and death, the last 24 hours have been the most hopeful of the entire pandemic.

On Tuesday, a 90-year-old Briton became the first person in the world to receive a clinically authorized, fully tested coronavirus vaccine. A few hours later, the U.S. Food and Drug Administration confirmed that the same vaccine, made by Pfizer and BioNTech, is safe and 95 percent effective. On Thursday the FDA’s vaccine advisory group will almost certainly approve the Pfizer vaccine, and by week’s end the first Americans should be getting inoculated. Other vaccines, starting with Moderna’s 90-percent-effective formulation, will soon follow.

In short, there is now a very bright light at the end of this dark, daunting tunnel. But amid all the encouraging vaccine news, a more immediate and no less important message should also be coming through: If you want to reach the end of the tunnel as soon as possible — or at all — do not remove your mask.

The more we mask up and keep our distance now, the faster the vaccines can make it safe for us to stop. The less we mask up and keep our distance now, the longer that process will take.

There are two reasons for this. The first, buried on page 48 of Tuesday’s FDA briefing documents, is a caveat that will define the pivotal months ahead. While Pfizer’s drug overwhelmingly prevents people from getting sick with COVID-19, we still don’t know if it prevents them from getting infected without showing symptoms — and then silently spreading the virus to others.

“Data are limited to assess the effect of the vaccine against transmission of SARS-CoV-2 from individuals who are infected despite vaccination,” the FDA explained. “Asymptomatic cases in combination with reduced mask-wearing and social distancing could result in significant continued transmission.”

A nurse speaks to a man before administering the Pfizer/BioNTech Covid-19 vaccine at a vaccination centre in Cardiff, UK on Dec. 8, 2020. (Justin Tallis/PA via AP)
A nurse speaks to a man before administering the Pfizer-BioNTech coronavirus vaccine on Tuesday in Cardiff, Wales. (Justin Tallis/PA via AP)

The second reason why Americans need to keep covering their mouths and noses was laid out in a new paper published in Health Affairs, co-authored by Dr. Rochelle Walensky of Massachusetts General Hospital, whom President-elect Joe Biden has chosen to run the Centers for Disease Control and Prevention.

When it comes to actually ending a plague in real time, the authors demonstrate mathematically, even the most effective vaccines have their limits. A far more important factor in determining the ultimate duration of the pandemic — and the toll it takes in the meantime — is how widely and rapidly the virus is spreading when vaccination begins.

“Bluntly stated, we’ll get out of this pandemic faster if we give the vaccine less work to do,” A. David Paltiel, one of the Health Affairs authors and a professor at the Yale School of Public Health, told the New York Times.

At first glance, both of these cautionary notes seem counterintuitive. Isn’t the whole point of a 95-percent-effective vaccine to stop 95 percent of infections and end the pandemic? And if people can’t get sick with COVID-19 anymore, that should mean they can’t spread it … right?

Not quite. Let’s tackle transmission first. Here’s what we know. A respiratory infection like the coronavirus starts in your nose. Once the virus gains entry, it starts to multiply rapidly, triggering the production of antibodies native to the moist membranes that line your nose, mouth, lungs and stomach. Next time you’re exposed to the virus, these antibodies (along with other immune cells) block it from getting past the nose and spreading to the rest of your body. So now you don’t get sick.

That’s how natural immunity works. But the initial coronavirus vaccines operate differently. They’re injected into your muscles and absorbed into your bloodstream — and that’s where they go on to stimulate the production of antibodies. Eventually, these antibodies circulate throughout your body and successfully ward off infection. Some end up in your nasal tissue.

But here’s what we don’t know yet: How many of these antibodies can be rushed to the nose in time to shut down the virus. “If the answer is not much, then viruses could bloom [there] — and be sneezed or breathed out to infect others” even if you don’t feel sick, the New York Times’ Apoorva Mandavilli recently explained.

A nurse administers the Pfizer-BioNTech COVID-19 vaccine at Guy's Hospital in London on Dec. 8, 2020. (Frank Augstein, Pool via AP)
A nurse administers the Pfizer-BioNTech vaccine on Tuesday at Guy’s Hospital in London. (Frank Augstein, Pool via AP)

To be clear, our current lack of data on whether the first coronavirus vaccines reduce transmission doesn’t mean they don’t reduce transmission. It simply means researchers haven’t had time to study the question yet. The initial trials were designed to track how many vaccinated people got sick with COVID-19. They weren’t designed to test whether the shots prevent the virus from spreading from person to person. Many vaccines do just that; others, like a newer whooping cough vaccine, may do less. It’s impossible to tell which camp the coronavirus vaccines fall into without more information, especially because the lungs — the site of severe symptoms — are easier for circulating antibodies to access and guard than the nose or throat.

Some initial signs are promising. According to a press release from the University of Oxford researchers who partnered with AstraZeneca on a third coronavirus vaccine, there was an “early indication” in their trials — not detailed with further data or peer-reviewed — that it “could reduce virus transmission from an observed reduction in asymptomatic infections.” Unlike Moderna and Pfizer, which only tested people who showed symptoms, Oxford researchers sent testing kits to U.K. participants weekly throughout the study to see whether their vaccine could reduce infections as well as illness. They claim to have found a lower asymptomatic infection rate in the vaccinated group than in the placebo group, which suggests that the former would be less likely to unwittingly spread the disease than the latter.

Likewise, one recent study showed that people who received an intramuscular flu shot had lots of antibodies in their noses, while a different study of COVID-19 patients found that the antibody levels in their saliva closely matched the levels in their blood — a hint, perhaps, that a strong immune response from a vaccine might also protect the nose and throat.

Fortunately, we should know more about vaccines and transmission soon. Both Pfizer and Moderna are planning to test participants’ blood samples for antibodies that target a part of the virus that is not in the vaccine — whose presence would signify they were infected with the active virus after vaccination. If fewer volunteers in the vaccinated group than in the placebo group have developed these antibodies, it would constitute “evidence,” a Pfizer spokesperson told Wired, “that the vaccine can prevent infection as well as disease.” Moderna, at least, should have results in “several weeks,” according to the Times.

A nurse holds a phial of the Pfizer-BioNTech COVID-19 vaccine at Guy's Hospital in London on Dec. 8, 2020. (Frank Augstein, Pool via AP)
A nurse holds a vial of the Pfizer-BioNTech vaccine. (Frank Augstein, Pool via AP)

A Stanford team, meanwhile, is planning to compare antibody levels in blood and saliva samples from Johnson & Johnson’s vaccine trial, and Dr. Larry Corey, an influential virologist at the Fred Hutchinson Cancer Research Center, has designed a study that could answer the transmission question by May by vaccinating thousands of on-campus college students and testing at least every other day for asymptomatic infections.

In the meantime, however, “we will not have sufficient concrete data to prove that this vaccine reduces transmission” when deployment begins, as Moderna chief medical officer Tal Zaks recently told Axios — and it will take many months for most Americans to be immunized. So “it’s important that we don’t change behavior solely on the basis of vaccination.”

How important? In November, CDC disease modelers compared a theoretical vaccine that stopped 95 percent of transmission with one that stopped no transmission at all. In the hypothetical scenario, inoculating seniors and other high-risk adults while cases are rising — as they are now — with a vaccine that kept people from getting sick but allowed transmission resulted in twice as many deaths as the one that blocked infection altogether.

And that’s not even taking the true scale of the virus’s current spread and the slower-than-expected pace of vaccine distribution into account. Earlier this week, David Leonhardt of the New York Times asked the authors of the Health Affairs study to “put their findings into terms that we nonscientists could understand.”

Vials are seen as an employee works on the coronavirus disease (COVID-19) vaccine at the Pfizer manufacturing facility in Kalamazoo, Michigan, U.S. (Pfizer/Handout via Reuters)
A worker with vials of the coronavirus vaccine at the Pfizer manufacturing facility in Kalamazoo, Mich. (Pfizer/Handout via Reuters)

The response was sobering. In an alternate universe in which the forthcoming vaccines were only 50 percent effective but the U.S. had managed to freeze its infection rate at about 35,000 new daily cases — the level back in early September — roughly 60,000 Americans would die of COVID-19 as mass immunization gradually took hold over the next six months.

But at the current level of infection in the U.S. — about 200,000 new daily cases — even the gold-standard, 95-percent-effective Pfizer vaccine, rolled out as scheduled, couldn’t prevent a bloodbath. According to the Health Affairs authors, nearly 10 million additional Americans would contract the virus in that scenario, and more than 160,000 would die.

That’s somewhere around 450,000 dead by the middle of 2021.

The bottom line is this: A return to something resembling normal existence is on the horizon, thanks to these remarkable vaccines. But we’re the ones with the power to determine how quickly we get there — and how many irreplaceable lives are lost before we do. We just have to keep wearing our masks.


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