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There’s a Lot We Don’t Know About the Promising Covid Vaccine

Experts celebrated the news that Pfizer’s vaccine could potentially prevent 90 percent of cases, but the road ahead is still very long and very uncertain.


Pfizer and BioNTech, a German biotechnology company, announced Monday that their coronavirus vaccine may be 90 percent effective at preventing Covid-19, according to early results. Although experts cautioned that more detailed results need to be released, they see it as a very promising development both for this vaccine and for other vaccines under development. It’s the first step in the monumentally complicated process of getting the population vaccinated—but only the first step. Manufacturing and distributing the vaccine will be just as challenging.

The two companies said in a press release that 94 participants in their phase 3 trial have had confirmed cases of Covid-19, but the vast majority of those confirmed cases happened among subjects receiving the placebo. These results have not been featured in a peer-reviewed publication, which is not especially surprising, since the trial is ongoing and the independent monitoring board may not have even shared all of the results with the companies yet.

However, these scant details leave the vaccine-desperate public with a lot of unanswered questions. For instance, how well does the vaccine prevent serious illness? The companies said it is effective at preventing the disease, Covid-19, but that means it may still be possible to be infected by the virus, SARS-CoV-2. These preliminary results focus on those who developed serious illness, but how many people in the trial have had asymptomatic or mildly symptomatic cases? And if 10 percent of the confirmed cases were among participants who received the vaccine, did it lessen the severity of their illness? Beyond the effectiveness of the vaccine itself, getting it to the people who need it is guaranteed to be a monumental task.

In spite of these unsettled questions, experts are cautiously optimistic about what these results could mean for this and for other Covid-19 vaccines. “My initial reaction is that this is excellent news,” said Dr. Andrea Cox, a professor in the infectious diseases division at Johns Hopkins University. “It’s a small number of people who are infected, and the trial is not complete,” she cautioned, but even if later infections make that percentage lower, it’s still encouraging that the vaccine seems to be working well. “We really can do pretty well with a vaccine that is even 60 percent effective,” she said, a point that other experts have also made.

Angela Rasmussen, a virologist at Columbia University, agreed. “It’s very encouraging,” she said. “I think there’s still a long way to go. This is based on an interim analysis and they haven’t actually showed the data,” she said, but “if it holds up in a larger population of people, that’s still a huge public health win.”

It’s not just good news for Pfizer. Several of the vaccines in the late stages of development similarly rely on creating antibodies to defend against the coronavirus. “This is really good news for many other vaccine manufacturers that have designed vaccines to elicit this neutralizing antibody response,” Cox said.

While it’s true that the preliminary results seem to focus on preventing severe disease, instead of curtailing all infections, that’s true of most vaccines, Cox said. Being able to stop a virus entirely is called “sterilizing immunity,” which she compares to a wall the virus can’t get surmount in order to enter our bodies. That level of immunity “is a very high bar, and we don’t expect most of our effective vaccines to work that way,” Cox said. More commonly, a vaccine “basically ratchets down the severity of the disease, which is really, really helpful.” After all, Cox pointed out, the goal isn’t to keep everyone from getting mildly ill; the goal is to prevent severe illness and death.

Vaccines also don’t work the same way for everyone; they aren’t as effective among older people, for example. In the Pfizer and BioNTech trial, Rasmussen said, “we don’t know how many of those people were in vulnerable groups that would need the vaccine arguably more. Especially if the main function of the vaccine is to protect against severe disease, you want to make sure that that is going to work just as well in an 80-year-old, or a 70-year-old, or somebody with a preexisting medical condition, as it works in a perfectly healthy 25-year-old.” And while the vaccines may prevent severe infection, there’s still much we don’t know about the long-term effects of mild illness, she said.

Pfizer and BioNTech will continue trials until 164 participants have contracted Covid-19, at which point they’ll do another analysis. They will not apply for an emergency use authorization to begin distributing the vaccine until two months of safety data have been collected—which won’t take place until the third week of November, at the earliest. So far, the companies say, there have been no serious safety concerns.

But even once a vaccine is proven effective, it will need to be manufactured and distributed—which will require a massive rollout plan and specific equipment like freezers to store the vaccine, which needs to be kept at at least –80 degrees Celsius. “There are going to be some significant challenges that we need to overcome once this vaccine is approved before it can be widely distributed enough to make a difference,” Rasmussen said. “And then long term—and this is true of all the vaccine candidates—there’s going to be a pretty steep hill to climb in terms of convincing people to actually get it.”

Back in May, 72 percent of American adults said they would get a SARS-CoV-2 vaccine if it were available—but that declined sharply to only 51 percent by September, as more people worried about a political push to rush vaccines to market before they’re ready. President Trump frequently promised a vaccine by Election Day, but the misinformation didn’t end last week. This morning, Vice President Mike Pence, the head of the White House coronavirus task force, incorrectly tweeted that the Pfizer-BioNTech vaccine “is EFFECTIVE, preventing infection in 90% of its volunteers.” (He also inaccurately portrayed this vaccine as part of the U.S. Operation Warp Speed project, when in fact the two companies developed the vaccine independently.)

Joe Biden has taken a much more measured approach to this news, writing in a statement that “the end of the battle against COVID-19 is still months away” and encouraging the public to continue taking every precaution against the virus.

Experts said that such an approach, based on science and current knowledge of the pandemic, will help boost trust in the vaccine’s safety and effectiveness. As Georges Benjamin, executive director of the American Public Health Association, recently told me, a Covid-19 vaccine “will help us, but it’s not the silver bullet. It is an important tool in our tool kit, and they’re going to have to be careful they don’t oversell it.”

At the same time, this news represents an important step forward for addressing both this and future pandemics. If it is successful, it will only be the third platform vaccine ever approved for use, and the first mRNA platform vaccine. Platform vaccines can be created quickly, which could affect our future epidemic responses dramatically.

Until these vaccines are proven safe and effective through rigorous, completed clinical trials, however, the battle is not yet won, and the virus is still spreading across the nation. We need to keep doing the same things we know are effective at curbing the pandemic, experts say—wearing a mask, keeping a distance, avoiding crowds and indoor gatherings, washing our hands. But news like this reminds us that the end is in sight, and we don’t have to live with this pandemic forever. Even once a vaccine arrives, we will continue to save lives by taking as many precautions as possible.

“I think the vaccine will be potentially excellent, but I think there are other ways we can do our part to make sure that we’re not putting others at risk,” Cox said.