Pfizer Says Its COVID-19 Vaccine Is 90 Percent Effective. What Happens Now?

Pfizer announced promising results from its coronavirus vaccine trial.
David Dee Delgado/Getty Images

The pharmaceuticals giant Pfizer announced Monday that its coronavirus vaccine is more than 90 percent effective, according to any early analysis of the data from a clinical trial involving 44,000 people. Results indicate that the vaccine protected test subjects for at least a month. In order to get a better sense for what this announcement could mean for combatting the pandemic, I spoke to Kathryn Stephenson, a professor at Harvard Medical School who directs the clinical trials unit for vaccine and virology research at the Beth Israel Deaconess Medical Center. This interview has been condensed and edited for clarity.

Aaron Mak: Why are these results noteworthy?

Kathryn Stephenson: In vaccine development, you never actually know if your vaccine is going to work until you test it in the field. There was promising data about all of these vaccines, at least promising data in animal studies and in the lab, but that doesn’t mean that’s going to translate to real life. Scientists have been looking at HIV vaccines for 30 years and have never shown proof of concepts that a vaccine could work. For that reason, it’s a really big deal. Yes, there’s a lot of caveats, but the fact that they were able to see such a big difference is a real proof of concept.

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What are the next steps?

There are many vaccines that are being tested, and we can’t just laser focus onto this one. This is just part of a bigger story of all of the vaccines in development. For this particular vaccine, before they can go to the FDA and present their data and ask for an Emergency Use Authorization, what they need to do is present two months of safety data. This was something that was agreed upon pretty much by all of the [companies doing] vaccine studies: that they weren’t going to jump the gun and they were actually going to wait for two months, as opposed to going in after, say, a few days. With the timeline for Pfizer, that would put them at about the end of this month. Around Thanksgiving is when they’ll hit that mark. They’ll submit all of their data packaged to the FDA for this Emergency Use Authorization. That’s the first step, but that’s a tiny step. Not much changes for most of us when that happens.

What are the big remaining questions that need to be answered about the Pfizer vaccine?

One of the biggest ones is the durability of this effect. They said that what they were able to observe so far is that the vaccine seems to work, and they measured that as soon as seven days after people got their second vaccine. What that can tell us is that over the course of a month or so after vaccination, people seem to be protected. Now, most of us when we get a vaccine are looking at a much longer time period. We are hopeful that it will at least cover us until the next season. With a measles vaccine, we’re hoping for decades of protection. That is a question that really remains to be answered, and that will depend on how long those antibodies and that really good immune response sticks around.

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Would the vaccine still be useful even if it turns out that protection only lasts for a month?

Absolutely. You can imagine a lot of scenarios where that would be useful going into surges and peaks of an epidemic or for vaccinating a bunch of college students a few weeks before they all go home for the holidays. There are a lot of scenarios where even transient protection is important. What we know from a lot of vaccines is even the ones that do wear off, oftentimes we can just boost them. After three months, you get another shot and you keep your levels up. That’s not a killer for any of these vaccines. If the immunity wears off, there’s a lot of ways we can troubleshoot that.

What do you think the distribution timeline might look like?

Certainly this fall it’s not going to be widely available. Looking forward to January 2021, if they have batches of this vaccine that are ready to go out, then they’re going to be distributed according to a national plan. There’s been recommendations and some strategy that’s been put forward for vaccine distribution. I think people agree that it will first go out to really high-risk groups, so people who are most at risk of getting infected, which would be front-line health care workers, ambulance drivers, first responders. Shortly after that, it would be people who are at increased risk for dying of COVID-19, so people with really severe risk factors, which are obesity and multiple comorbidities like heart disease and cancer, and then people who are 65 and older. For most people, we’re not going to be first in line and we’re going to have to wait. It’s not going to be the type of thing where you can just go down to your local pharmacy and ask for it. It’s going to be distributed and essentially rationed in the beginning.

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Why can’t we just rely on the Pfizer vaccine?

This vaccine in particular is a little bit delicate. You have to keep it really cold when you store it—minus 80 degrees Celsius. That is very tough for resource-poor settings, and it’s actually tough for a lot of regular clinics in most communities. They’re going to have to develop a lot of logistics to make that feasible. One of the things that people are hoping for is that one of the other vaccines will be able to be stored just in your refrigerator, because those of course would be much easier to transport and get out to rural clinics.

The other thing is we really don’t know very much at all about this Pfizer data. We don’t know if it was only in one age group. Elderly people over 65 typically have lower antibody levels after vaccination. As you get older, your immune system just isn’t as robust. Oftentimes, to be protected, older folks have to get either a higher dose of a vaccine or maybe an extra booster. We don’t know yet if in their data they’re able to even see that. Probably not—they probably have to wait. There may be a scenario where their vaccine is great in people under 65, but over 65 it’s not as potent. Then maybe there’ll be another vaccine in the portfolio that is more potent, particularly within that age group. Similarly, think about pregnant women or women who might become pregnant. For the most part, pregnant and breastfeeding women are excluded from these studies, as are kids under 12, and the vaccines may have very different profiles in those different groups.

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Then, the biggest thing is just to think about numbers. If one vaccine company says, “We have 15 million doses available,” and then another vaccine turns out to be pretty good and it also has 15 million, then right there you’ve doubled your national inventory. We are so far from the numbers that you would need to cover everybody in the U.S. and globally. The more vaccines you have, the more products you have on your shelf.

Will these other pharmaceutical companies be able to steer their research so that they develop vaccines that are, say, more resilient in different temperatures or more effective for certain age groups?

The current portfolio of vaccines that are in efficacy testing in the United States and Europe include a pretty wide range of platforms, some of which can be stored at refrigerator temperature. For example, the Johnson & Johnson vaccine can be stored at 2 to 8 degrees Celsius. The portfolio that’s developed over time with all of these different companies jumping in is rational. Some of the leadership has been working on this, and some of it is also just organic that different companies come to the table with different platforms. They do already right now cover a wide range of doses, adverse event profiles, storage conditions. There’s a great diversity of them.

Future Tense is a partnership of SlateNew America, and Arizona State University that examines emerging technologies, public policy, and society.


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