01/29/2021

Everything You Want To Know About COVID-19 Vaccines

17:17 minutes

a woman wearing a mask in a lab coat wearing a stethoscope adminsters a vaccine shot to an older man, also wearing a mask
Credit: Shutterstock

This story is part of Science Friday’s coverage on the novel coronavirus, the agent of the disease COVID-19. Listen to experts discuss the spread, outbreak response, and treatment.


The U.S. has been vaccinating people against COVID-19 for a little over a month. While there have been plenty of hiccups, over 20 million people in the country have received at least one dose of either the Pfizer-BioNTech or the Moderna shots.

For the past few weeks, Science Friday has been collecting your questions about the COVID-19 vaccines on the SciFri VoxPop App—and we heard from a lot of listeners. The questions and concerns ranged from if people with antibodies should get vaccinated to if the vaccines are safe for pregnant people.

Joining Ira to tackle these listener questions is Benhur Lee, professor of microbiology at the Icahn School of Medicine at Mount Sinai in New York City.

Answers have been edited and condensed for clarity.

If you receive the COVID-19 vaccine, can you still transmit COVID-19 to others?
Benhur Lee: It is likely that once you have sufficient immunity—once given a full dose of the two shots currently needed—that if you do get infected, the amount of viruses will be quite low, so the chance of transmitting will be low. 

But we do not have the data yet to say whether or not you would transmit the virus. Trials are being done to address that very question. For now, it would be safe to assume that you can transmit it, so take those precautions. 

If someone has already gotten COVID-19 and has tested positive and recovered, are they supposed to get a COVID-19 vaccine anyway?
BL: Yes. The current recommendation is to get a vaccine. Many healthcare workers have gotten infected and recovered, and they are still required to have their full dose of vaccines as part of working in that environment. 

With several different vaccines available, is one more effective than the other? How are they different? Does it matter which one you get?
BL: There’s no significant difference between Pfizer and Moderna. They’re essentially identical and they’re both very effective.

Approved vaccines, according to WHO recommendations, have to be at least 50% efficacious. The Pfizer and Moderna vaccines are more than 90% effective in preventing infection.

They are both based on an mRNA vaccine platform. This is a new vaccine method, and it works surprisingly well. It doesn’t use any part of the infectious viruses at all. It’s just delivering instructions to make that particular protein, the spiked protein that’s outside of the virus [the corona]. That helps your immune system to make antibodies against the spikes. So there’s no significant difference between the two.

The AstraZeneca and Johnson & Johnson vaccines that are coming soon are virally-vectored vaccines. That means the instructions for making the relevant parts of the coronavirus are put into a very safe virus vector that does not cause disease, but it does irritate your immune system to think that the virus is coming in. And so those vaccines make the right kind of antibodies as well.

Find out more about what researchers know about virally-vectored vaccines.

How do mRNA vaccines work? How is it different from other vaccines, like the smallpox vaccine?
BL: The usual vaccines, like the smallpox vaccine, is what we call a live attenuated vaccine. Back in the day, you would just passage the virus for a long time [mixing the virus cell with chicken embryo cells], run it through hundreds of passages and cell lines, and eventually it loses all its virulence genes [this modified version of the virus gets very good at killing chicken egg cells, but gets much worse at killing human cells. Learn more via the CDC]. So it turns into a very weakened version of the virus. 

This mRNA vaccine is a brand new technology. There are no viruses involved at all in it. All it has is just the messenger, the transcript for telling the cell how to make the protein.

And so in biology, DNA codes instructions and then it’s transcribed to the messenger. This intermediate nucleic acid tells the protein machinery in the cell to produce the actual virus spike. That’s the antigen that your immune system sees, and the antibodies will block the actual virus from coming in. So it’s very clever. You use no parts of the virus in the vaccine.

It’s very safe because there’s essentially no DNA in the vaccine, just mRNA, which are the intermediate instructions. And that’s why it works so well, because they’ve optimized ways to make the instructions efficiently recognized by yourself. So it’s actually using your own body as a bioreactor, making your muscle cells actually produce the protein so that your immune system recognizes the virus.

Is the second dose of the vaccine the same as the first in composition and amount? Or is the second dose different?
BL: The answer is essentially yes. The second dose is essentially the same as the first dose, and it just acts as a booster. The first one primes your immune system to start making the antibodies. And the second one helps your immune system memorize the intruder. At that point, it’s seen it twice, it gets its army together, and then it’s ready to go. So when the actual virus comes in, your body will start proliferating the cells that make your antibodies to help protect you against the virus.

How long does protection from the vaccine last? Am I going to have to have a shot a year from now?
BL: I want to remind people that this is a one-year-old disease. Scientists are working on addressing these questions. But historically, what we can say is that, once you’ve been infected with coronavirus and you generate antibodies, they usually hang around for a few years. It’s not going to be a one-year deal.

We know about the four coronaviruses that are already endemic to human populations, 25% of seasonal colds are caused by coronaviruses. Previously, we just didn’t care before about making vaccines against sniffles. But we know that these antibodies from these seasonal colds hang around. They’re good for a few years, give or take, until the virus changes into a new genotype, for example. And then you get reinfected, and then you make a new set of antibodies. 

So I would say, let’s wait and see how fast this virus evolves and whether we need updates or not.

“The second dose is essentially the same as the first dose, and it just acts as a booster. The first one primes your immune system to start making the antibodies. And the second one helps your immune system memorize the intruder.”

Is the coronavirus going to mutate every year like the common flu?
BL: All viruses mutate. That’s what they do. That’s their way of living. They’re small little things. They replicate in billions of copies. So there’s nothing wrong about mutation. And by that, I mean most mutations are actually bad for the virus, so they don’t necessarily survive. 

The question is, will these future mutations allow the virus to affect someone who is “immune?” There are some indications now that we might be worried about some of these new variants. But I want to say that it’s not like an on-off switch.

Most of these vaccines generate very high concentrations of antibodies. They generate more antibodies than we actually need, so they’ll still provide some protection. And as we speak, Moderna is discussing how they can update their vaccines easily. But will the virus mutate every year? I don’t know. Let’s wait and see. Likely not.

What do you advise those to do if they are either pregnant or plan to have children soon? Should they take the vaccine? And can you explain more about how the mRNA components will not affect reproductive systems?
BL: Trials are generally designed not to include pregnant people because they are in a special research category. But having said that, we administer vaccines all the time to pregnant people—vaccines for influenza, pertussis. So it’s not as if they can’t receive vaccines.

The mRNA vaccine is very safe. It’s just the intermediate instructions on how to make the protein. There’s zero chance that it will affect your genes, your genetic composition. It’s temporary, and it’ll eventually degrade. So, the only plus side is that when the parent makes the antibodies, they can actually transfer some of the antibodies to the fetus.

So in the first six months of an infant’s life, a lot of protection in the child is actually from the maternal antibodies that’s transferred through the placenta. So while the vaccine trials have not specifically included those who are pregnant, the American Association of Obstetricians and Gynecologists Foundation have not said that pregnant people should not receive the vaccine.

Let’s say you test positive for the virus, and you’re in the early stages of it (symptomatic or asymptomatic). Would it help to get the vaccine anyhow to fight off the infection by trying to flood the body with the vaccine instead of having the virus multiply?
BL: I think it’s difficult to generalize about such questions. Because if you are truly asymptomatic and healthy and stuff, one must remember that the vast majority of infections result in mild or asymptomatic disease. So your immune system can take care of it. 

But if you are still in high-risk groups, we do have effective treatments now that if they’re administered early–the monoclonals have been shown to work. A lot of treatments are effective when you start them early.

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Segment Guests

Benhur Lee

Benhur Lee is a professor and chair in Microbiology in the Icahn School of Medicine of Mt. Sinai Hospital in New York, New York.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. The US has been vaccinating people, or trying to vaccinate people, against COVID-19 for about a month now. And while there have been plenty of hiccups, about 20 million people in the country have received at least one dose. For the past few weeks, we’ve been collecting your questions about the COVID-19 vaccines on our Science Friday VoxPop app, and boy, did we hear from a lot of you.

So today, we’re going to tackle what you want to know about these vaccines. Joining me to answer your questions is my guest Dr. Benhur Lee, professor in microbiology in the Icahn School of Medicine of Mount Sinai Hospital in New York.

Welcome back to Science Friday.

BENHUR LEE: Glad to be back.

IRA FLATOW: Nice to have you. Boy, there are a lot of questions, so I want to get right into them. Let me start off with the basics. Here’s a question we got from listener Nancy in Ohio.

NANCY: If you receive the COVID-19 vaccine, can you still transmit COVID-19 to others?

BENHUR LEE: Well, let me just say first that the initial trials were not designed to test whether the vaccine can prevent transmission. It was designed to test whether the vaccine can prevent you getting infected. It’s very efficacious from preventing infection.

That being said, it is likely that once you have sufficient immunity, once a full dose is given, that, at a minimum, if you do get infected, the amount of viruses will be quite low, so the chance of transmitting will be low. But we do not have the data, one way or another, yet to say whether this is fail-safe that you cannot indeed transmit the virus. So I would say, let’s wait for the data to come in, because trials are being done to address that very point you just mentioned.

IRA FLATOW: Yeah. It would be safe to assume then, just for safety, that you can transmit it so take those precautions.

BENHUR LEE: Yes, I think so.

IRA FLATOW: A question from Paul in New Haven, Connecticut.

PAUL: If someone has already gotten COVID-19 and has tested positive and recovered, are they supposed to get a COVID-19 vaccine anyway?

BENHUR LEE: I think the current recommendations are to indeed get a vaccine because right now it’s just– we all have to remember this is a one-year-old disease. And we’re asking a lot from science to try to address it. But there’s no contraindication right now. And in fact, if you work in health care settings, many people have gotten infected and recovered, and they will still require you to have your full dose of vaccines as part of working in this environment. So yes.

IRA FLATOW: Yeah, OK, let’s go to question three. As we know, people who have been vaccinated against COVID-19 in the US have received either the Pfizer-BioNTech vaccine or the Moderna one. We know that. So let’s hear this question from Ioanna in California.

IOANNA: With several different vaccines available, is one more effective than the other? How are they different? Does it matter which one you get?

BENHUR LEE: All right, if Ira has two hours, I can go into the various vaccines, but we don’t.

[LAUGHTER]

So let me just address the big field that people might have heard about. I just want to preface it by saying, if it has been approved by legitimate national authority, all the vaccines, if they follow WHO recommendations, have to be at least 50% efficacious. The two big ones that you hear about that’s approved in the United States are the Pfizer and Moderna vaccines, and those are more than 90% effective in preventing infection.

They are both based on what you call an mRNA vaccine platform, which we’ll get into later, probably. And this is a new vaccine modality, and it really does work, and surprisingly well. It’s not based on using any part of the infectious viruses all, it’s just delivering instructions to make that particular protein, the spiked protein that’s outside of the virus, the corona, so to speak, when you talk about coronaviruses, and that helps your immune system to make antibodies against the spikes.

So there’s no significant difference between Pfizer and Moderna. They’re essentially identical in terms– not proprietary, I mean, not in terms of the formulation and even sequence per se, but they’re both very efficacious. The AstraZeneca and probably Johnson & Johnson that’s coming down, they are [? virally-vectored ?] vaccines. That means the instructions for making the relevant parts of the coronavirus is put into a very safe virus vector, an adenovirus vector of some kind that does not cause disease or is replication incompetent, but it does stuff like irritate your immune system to think that the virus is coming in. And so they make the right kind of antibodies as well.

And then the last one is you have the killed vaccines from China, the CoronaVac, and that’s very traditional, like how the polio vaccine was back in the days where you just grew up vats of viruses, and you inactivated, and you put it with what we call an adjuvant, something to stimulate your immune system, and you get responses. The efficacy of that one is just above 50% for reasons that we are unclear, because the data has not been fully released. But that’s what’s up there. I will say any vaccine is better than none.

IRA FLATOW: Let’s go to Tom in Bandera, Texas, who has a good follow up to that question.

TOM: I think I sort of understand how our current vaccines for, like, smallpox work, but I’m not sure I understand what it is that happens with these mRNA vaccines. Can you help explain that to me?

BENHUR LEE: Yes. So continuing on the theme, the usual vaccines like smallpox is actually what we call a live attenuated vaccine that back in the days, you would just passage virus for a long time, hundreds of passages and cell lines, and eventually they lose all their virulence genes. So this one is like a very weakened version of the virus. This mRNA vaccine is a brand new technology so there are no viruses involved at all. It’s just the messenger, the transcript for telling the cell how to make the protein.

And so in biology, you have DNA codes instructions and then it’s transcribed to messenger. This intermediate nucleic acid tells the protein machinery in the cell to produce the actual virus spike. That’s the antigen that your immune system sees, and this is the antibodies that will block the actual virus from coming in. So it’s very clever. You use no parts of the virus.

It is very safe because there’s essentially no DNA, just mRNA, the intermediate instructions. And that’s why it works so well because they’ve optimized ways to make the instructions efficiently recognized by yourself. So it’s actually using your own body as a bioreactor, making your muscle cells to actually produce the protein so that your immune system recognizes.

IRA FLATOW: Well, I hope to get my shot and be turned into a bioreactor very soon. Come on. That’s a great explanation. Let’s go to Julia. Julia from Pennsylvania is up next.

JULIA: Is the second dose of the vaccine the same as the first in composition and amount? Or is the second dose different?

BENHUR LEE: To save time, I’ll just talk about the Pfizer and Moderna, and the answer is essentially yes. The second dose is essentially the same as the first dose, and you just need a booster. So the first one is to prime your immune system, stop making the antibodies. And the second one is to [INAUDIBLE] your immune system memorize that now I’ve seen it twice, I got my army together, and then I’m ready to go. So when the actual virus comes in, the B cells, which are the cells that make your antibodies, will start proliferating a lot to help protect you against a virus.

IRA FLATOW: Which raises the question for me, and a lot of listeners are wondering about this, can you get your first shot from Pfizer and your second from Moderna, for example, Andrew from Equality, Alabama wants to know.

ANDREW: I understand that both the Pfizer and Moderna vaccines are based upon the same RNA sequence. That being the case, does it matter very much which booster type of shot you receive?

BENHUR LEE: Boy, lots of people are asking their questions and they’re looking into it. And let me just say the trials are not designed that way, and nor are they approved that way. So instead of speculating, I will withhold judgment, because I don’t want to confuse the audience with a lot of subtleties that may go wrong. I mean, in effect, the Pfizer and Moderna are sort of the same and can–

IRA FLATOW: We will evoke the Fauci rule, which is what he said, if you don’t know the answer, say you–

BENHUR LEE: Yes.

IRA FLATOW: –don’t know it, right?

BENHUR LEE: Exactly.

IRA FLATOW: We’ll call it the Fauci rule from now on. Let’s go to a question from listener Peter about how antibodies may interact with the vaccine.

PETER: My wife and I live in Manhattan. And next week, she’ll be eligible to receive the COVID-19 vaccine. In July and December, she tested negative for COVID-19 on the diagnostic test, but positive for antibodies. Should her positive antibody status be taken into consideration in receiving the COVID-19 vaccine?

BENHUR LEE: Yeah, this is similar to one of your earlier questions. So there’s no contraindication, once again, that just because you have recovered from an infection– so the fact that she has antibodies means she was at one time infected. And so like I said, if you work in a health care facility, and depending on what category of risk you’re under, you are encouraged to actually receive the vaccine. So if you’re scheduled for it, I would receive it, and there’s no contraindication against it.

IRA FLATOW: Listener Darryl from Louisville, Kentucky has this question.

DARRYL: I’m going to be getting my shot. I’m over 70 soon. I wonder how long it’s going to last? Am I going to have to have a shot a year from now?

BENHUR LEE: Invoking the Fauci rule, like you mentioned earlier, I just want to remind people that this is a one-year-old disease. So people are asking a lot of questions that scientists are trying to address. But historically, what we can say is that coronavirus, once you’ve been infected with it and you generate antibodies, they usually hang around for a few years. It’s not going to be a one-year deal, because from what we know about the four coronaviruses that are already endemic in the human populations, and this is may not know, but 25% of seasonal colds are caused by coronaviruses.

It’s just that we didn’t care before about making vaccines against sniffles. But based on those data, these antibodies, they hang around. They’re good for a few years, give or take, until the virus changes into a new genotype, for example. And then you get reinfected, and then you make a new set of antibodies. So I would say, let’s wait and see how fast this virus evolve and whether we need updates or not.

IRA FLATOW: Listener Keenan from Salt Lake City is up next.

KEENAN: Is the coronavirus going to mutate every year like the common flu?

BENHUR LEE: That’s a great question, and one is hearing a lot of things on the internet and social media. All viruses mutate. That’s what they do. That’s their way of living. They’re small little things. They replicate in billions of copies. So there’s nothing wrong about mutation, and most mutations are not fit.

And by that, I mean most mutations are actually bad for the virus, and so they don’t necessarily work. The question is, do you get the fit mutations that will allow the virus to escape the immunity? And there are some indications now that we might be worried about some of these new variants that we heard about. But I want to say that it’s not like an on-off switch.

Most of these vaccines generate very high titer of antibodies. So when you hear things out there that this is you need five or more antibodies, that’s fine because these vaccines elicit much higher titer of antibodies then we do need, so they’ll still provide some protection. And as we speak, Moderna is discussing about how do they update their vaccines easily. But for right now, every year, I don’t know. Let’s wait and see. Likely not.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios. In case you just joined us, we’re talking with Dr. Benhur Lee, professor in microbiology in the Icahn School of Medicine of Mount Sinai Hospital in New York answering your questions about the vaccines. A lot of people are asking about kids, and children, and pregnancy. Let me go to Kim in Honolulu who has a question about pregnancy.

KIM: What do you advise young mothers or upcoming mothers to do if they are either pregnant or plan to have children soon? Should they take the vaccine? And can you explain more about how the mRNA components will not affect reproductive systems.

BENHUR LEE: That’s a great question. Let me just say that trials are designed, in general, not to include pregnant women because they have a special category. But having said that, we do administer vaccines all the time to pregnant women, influenza, pertussis. So it’s not as if they can receive vaccines.

The mRNA vaccine is very safe, like I said. It’s just the intermediate instructions on making the protein. So there’s no chance, zero, that that will affect your genes, your genetic composition. It’s not a retrovirus, so it’s temporary, basically, and it’ll eventually degrade. So the only plus side is that when you make the antibodies, the mother can actually transfer some of the antibodies to the child, the fetus.

And so in the first six months of an infant’s life, a lot of protection is actually from the maternal antibodies that’s transferred through the placenta. So those are the good things that can happen to a child if the mother received the vaccine. So while the trials have not specifically included pregnancy, the major health organization American Association OB/GYN, have not said that it was contraindicated to pregnant women either.

IRA FLATOW: I want to sneak in one last question of my own, because I was thinking about this. Let’s say you test positive for the virus, and you’re in the early stages of it. Would it help to get the vaccine anyhow to fight off the infection by trying to flood the body with the vaccine instead of having the virus multiply?

BENHUR LEE: Oh, boy. That’s a good question. So you mean, like, if you’re symptomatic or you know you have been just exposed?

IRA FLATOW: Yeah. If you’re early symptomatic or you’re asymptomatic and you know you’ve been exposed, you’ve tested positive, would it help to get that vaccine and get the mRNA moving and flooding the body with the good stuff sort of in competition with the virus?

BENHUR LEE: That may be true. So invoking the Fauci rule again, I can only–

[LAUGHTER]

–speculate. I think it’s difficult to generalize about such questions. Because if you are truly asymptomatic and healthy and stuff, one must remember that most– not to belittle this at all, but the vast majority of infections results in mild or asymptomatic disease.

So your immune system is fine to take care of it. But if you are still in high-risk groups and something that we do have treatments now that if done early– so I would focus on those treatments that are effective, the monoclonals that have been shown to work. A lot of treatments are effective when you start it early.

IRA FLATOW: So many questions, so little time, as always, Dr. Lee. Thank you very much for wading into this with us.

BENHUR LEE: Thank you, Ira. I appreciate all your listeners’ questions.

IRA FLATOW: Dr. Benhur Lee, professor in microbiology in the Icahn School of Medicine. That’s at Mount Sinai Hospital in New York. And if you have any lingering questions about COVID-19 vaccines that did not get answered today, please let us know. We’re planning to do more segments like this one. So send us your questions, and you can do that with the Science Friday VoxPop app wherever you get your apps.

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