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Dr. Leana Wen On The Science Of COVID-19 Vaccine


Now let's get to some of your questions about the COVID-19 vaccines. A lot of people wanted a refresher on the basic science behind the shots. To help us get some answers, we called Dr. Leana Wen. She is a practicing physician and former health commissioner for the city of Baltimore. She's also a contributing columnist for The Washington Post, where she writes about public health and health policy. And she is with us now.

Dr. Wen, thank you so much for talking with us.

LEANA WEN: Of course. Glad to join you.

MARTIN: So I'd like to begin with this basic question. Just what is a vaccine, and how does it work in the body?

WEN: It's a great question because we are talking about vaccines every day. And I think it's important for us to start with a baseline that vaccines train our immune systems to fight a particular illness. So in the case of COVID-19, there are different ways to get protection, to get immunity. You could be exposed to COVID-19 and recover, and you can make antibodies that help to fight the infection if you're exposed to it again. Well, vaccines do that work as well but without first having to make us sick with the disease.

MARTIN: And listener Sarang Bhatt asked via Twitter, should I be concerned with which manufacturer's vaccine I get, Pfizer or Moderna? What can you tell us about that? Do they work differently?

WEN: So they work via a similar mechanism. They are both shown to be very safe and highly efficacious - extraordinarily efficacious, actually - 94 to 95% effective in preventing COVID-19. And so right now, people who have the option to take a - or have the ability to take a vaccine, you should take whatever vaccine is available to you, and again, because they are both safe and appear to be highly efficacious.

MARTIN: And what's the purpose of two vaccine shots? Why does it need to be taken in two doses?

WEN: Yeah, so both the Pfizer and the Moderna vaccine require two doses. The Pfizer is a second dose three weeks after the first, and the Moderna is four weeks after the first. And the reason is that the first is a primer shot. The second is the booster shot. And that is how the vaccine is studied. There is some evidence that after the first shot, you do get some level of immunity, but we don't know how long that lasts. And it certainly is not anywhere approaching 94 to 95%. And so that's why to get the full effect of the vaccine, you do need both shots of it.

MARTIN: And listener Hans Vicente in Florida asks, can the second COVID vaccine be from a different manufacturer?

WEN: It's a really good question, and the answer is no. I mean, in theory, maybe it could be because they are a similar mechanism, but that's not how they're studied. And there are some differences between these vaccines such that nobody, the manufacturers nor public health experts, would recommend that you get a second vaccine from a different manufacturer. When you get the vaccine the first time, you have a card. You can also take a picture of it. Just make sure that you write down which manufacturer it is so that you make sure that the second shot that you have is from the same one.

This (inaudible) even more important over time. I hope that in the next couple of months, we'll get additional vaccine candidates that come online. Those other candidates are not mRNA vaccines. They work through different mechanisms. So it's going to be even more important that if you get a vaccine of one type that you make sure to get the second dose of that with the same type as well.

MARTIN: Oh, that's important information. So let's get into questions about side effects and who should or should not get the Pfizer on Moderna shots. First, are there known side effects?

WEN: So there are side effects of both the Pfizer and the Moderna vaccine. The side effects can be broken down into two categories. One is what happens at the injection site. So you could have pain, redness, swelling at the injection site. Then there are also what's called these systemic symptoms - basically, flu-like symptoms. You could get body aches, muscle aches. You could get fevers, chills, fatigue.

All of these symptoms are temporary. They last for hours to at most a few days. They may be uncomfortable for a short time, but they are nothing in comparison to what happens if somebody gets severe effects from coronavirus.

MARTIN: And we've also had listeners ask if people in their family who have had allergic reactions to penicillin or to previous vaccines should get the COVID shots. What can we say here?

WEN: It's a challenging place that we're at here because this is a new vaccine. And we have seen some examples of allergic reactions. It's two individuals with allergic reactions so far in the U.S. and two in the U.K. to the Pfizer vaccine. Allergic reactions to vaccines are rare, but they do happen - and emphasizing again that these are temporary, and we know how to treat allergic reactions should they occur. They're much easier to treat than if somebody became severely ill from coronavirus.

Right now, the recommendation by the FDA and the CDC - which, again, could change once we get more information - is that individuals who have had severe allergic reactions to previous vaccines should not get the vaccine right now. But those who have allergies to other substances - and many people have food or medication allergies - that they should still be able to get the vaccine. We just want to make sure that we are observing people for at least 15 minutes after that because if they are to have an allergic reaction, they will have it in a short period of time. And if they are receiving the vaccine in a health care setting or with health care providers around, that would be safe.

MARTIN: Finally, listener Elaine Braverman in Arlington, Va., had a question about how long the vaccines will be effective.

WEN: It's an excellent question that I don't yet have the answer to. So we do believe that the vaccine will be effective for at least 120 days, or specifically 119 days. That's what has been studied thus far. These are new vaccines. We don't yet know exactly how long they last. But again, that underscores why these continuing research studies will be really important. And we, again, may find that one vaccine is - will last for longer than another. We may find that certain vaccines require a booster shot in a similar way that we need for tetanus. Maybe they'll even be annual shots, as we do for the flu.

But I hope if it's any message that I can leave for everyone, it's that you should get the vaccine when it's your turn. This is our best chance for ending this pandemic. And right now, when we have 3,000, soon to be more than 4,000 people dying per day, this is absolutely urgent.

MARTIN: That was Dr. Leana Wen. She's a former health commissioner for the city of Baltimore, a practicing physician now and a public health columnist for The Washington Post. Dr. Leana Wen, thank you so much for talking with us and sharing your expertise today.

WEN: Thank you, Michel.