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Understanding the COVID-19 Vaccines
Hana El Sahly, M.D.
December 24, 2020

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Dr. Hana El Sahly is associate professor of molecular virology and microbiology in the Vaccine and Treatment and Evaluation Unit at the Baylor College of Medicine in Houston. Dr. El Sahly is the chairperson of the U.S. Food and Drug Administration (FDA) Vaccines and Related Biological Products Advisory Committee, the committee that makes vaccine recommendations to the FDA, and was also the lead investigator for the phase III trial for the Moderna COVID-19 vaccine. Because of her role in studying the Moderna vaccine, Dr. El Sahly recused herself from the committee’s review of COVID-19 vaccines. In this podcast, she talks to us about both the Pfizer-BioNTech and Moderna COVID-19 vaccines that have been granted emergency authorization by the FDA.

Listen to the podcast to hear Dr. El Sahly explain:

  • how mRNA vaccines work
  • the differences between the Pfizer-BioNTech and Moderna vaccines
  • the safety and effectiveness of the vaccines for people with weakened immune systems
  • why someone who’s been vaccinated still needs to wear a mask and practice social distancing

Running time: 19:22

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Show Full Transcript

Jamie DePolo: Hello! Thanks for listening. Our guest today is Dr. Hana El Sahly, associate professor of molecular virology and microbiology in the Vaccine and Treatment and Evaluation Unit at the Baylor College of Medicine in Houston. Dr. El Sahly is the chairperson of the U.S. Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee — the committee that makes vaccine recommendations to the FDA — and was also the lead investigator for the phase III trial for the Moderna COVID vaccine. Because of her role in studying the Moderna vaccine, Dr. El Sahly recused herself from the committee’s review of COVID-19 vaccines. 

She joins us today to discuss both the Pfizer and Moderna COVID-19 vaccines that have been granted emergency authorization by the FDA and what that means for people diagnosed with breast cancer.

Dr. El Sahly, thank you so much for joining us to talk about this very important topic.

Dr. Hana El Sahly: Thank you, Jamie, for inviting me.

Jamie DePolo: So, to start with, I know both the Pfizer-BioNTech and the Moderna COVID vaccines are messenger RNA, or shorthand, mRNA vaccines. So, can you explain how an mRNA vaccine works and how it’s different from a live virus vaccine?

Dr. Hana El Sahly: Sure. They are very different. A live virus vaccine replicates in the human body, but messenger RNA is not a virus. It’s the code for one of the proteins of the virus. It often happens that we vaccinate people with a particular protein expressed from the virus. Here, we are along similar line. The messenger RNA is the code that gets injected — encapsulated in a lipid component — as a vaccine, and once it’s in the body, our cells produce the protein. And from there on, the sequence is kind of similar to what happens when we get a protein vaccine. So, in essence, this particular technology allows the expression of a protein once in the body and does not require a live virus and is not a live virus.

Jamie DePolo: Okay, and that should set some people’s minds at ease because they’re not being injected with the virus, like the flu vaccine. It’s just one protein that then encourages the body to sort of respond to that particular protein. Is that correct? Am I understanding that right?

Dr. Hana El Sahly: That is correct, but I would also like to iterate that most flu vaccines we receive also are protein-based. There is one only that is live virus. And it’s mostly given for children. Yeah.

Jamie DePolo: Oh, okay. Got it. Okay. My mistake. Sorry about that.

Dr. Hana El Sahly: The majority of flu vaccines are protein. It’s inactivated virus, meaning it just has parts of the virus that are not live, and they are enriched for one of these protein called the hemagglutinin, which we try to mount a good antibody response against. That’s a flu question.

Jamie DePolo: Okay. Thank you. Sorry for going off on that tangent.

Now, I know that the Pfizer and the Moderna vaccines are fairly similar, but there are some differences. So, could you talk about what those differences are?

Dr. Hana El Sahly: Sure. As you mentioned, the two vaccines are similar in that they are trying to allow the body to express an immune response against the spike protein of the virus. They are both mRNA, and they both have a lipid nanoparticle component. The difference is, in the lipid nanoparticle component of the Moderna vaccine has one component of its lipid particle that is proprietary, and it allows for its stability at different temperatures. So, this is where the difference lies. 

From there on, this minor difference in composition also translates into the temperature at which the vaccine is stable. The Pfizer-BioNTech needs to be stored at -80 degrees until it’s thawed and administered to the person, while the Moderna one can stay in a refrigerator temperature — 2 to 4 degrees — up to a month, which sort of facilitates its widespread use in certain locations. The Pfizer-BioNTech vaccine is administered in two shots separated by 21 days. The Moderna vaccine is administered as two shots separated by 28 days. And the Pfizer vaccine is granted authorization from age 16 and older. Editor's Note: On May 10, 2021, the FDA authorized the use of the Pfizer-BioNTech vaccine in people 12 and older. The Moderna one is granted authorization from age 18 years and older.

Jamie DePolo: Okay. Thank you. Now, one of the top questions that’s come up in our Community is about both the safety and the effectiveness of these COVID vaccines for people with weakened immune systems. So, I have a two-part question for you. So, do we know that the COVID vaccines are considered safe for people with weakened immune systems — so, say somebody who’s being treated with chemotherapy for cancer? And will the vaccines be able to actually stimulate an immune response in somebody with a weakened immune system?

Dr. Hana El Sahly: In the clinical trials that tested the safety and efficacy of these vaccines, people who had active cancer and are in chemotherapy cycles were excluded. If they were in remission, they were allowed into these clinical trials. So, the short answer is that there are no data specifically in these special populations. However, these individuals do stand to benefit from the vaccines because they are in the higher risk category of getting complications of disease. We do extrapolate to these populations otherwise. For example, I don't know that we study for the tetanus in every population, or every other vaccine in these populations. But nonetheless, if they are safe and effective, we tend to administer them to these individuals, and I think the Pfizer and Moderna are no different. These populations stand to benefit because they are in the CDC-designated group at higher risk of complications, and they can receive those vaccines.

Jamie DePolo: Okay. Okay. Thank you. Now, could you tell us the side effects of the vaccine? I know people have talked about that the part two of the vaccines seem to cause a few more side effects than part one? And injection site pain seems to be a big one. But could you talk about some of the other ones?

Dr. Hana El Sahly: Yes. The injection site pain we did see with these vaccines, but they are not out of line compared to other vaccines, and they do tend to go away. It’s local, it’s painful, and then it goes away. The slightly different observation with these vaccines is that following dose two, we found that there’s a higher frequency — meaning a higher proportion of people — end up with low-grade fevers, fatigue, headache, malaise. As I mentioned, increased from dose one, and we see it more in dose two. These reactions tend to occur within a day or two after administering the second shot, and they tend to go away also within two days after their occurrence.

Jamie DePolo: Okay. Okay. Thank you. It sounds a little bit… like, I personally had the Shingrix vaccine, which is also two shots more than a couple weeks apart — longer apart. But the second dose, the second shot, definitely caused a little bit more pain and a little bit more achiness than the first. So, I don't know if it’s fair to equate it to that, but I’m sure a lot of people who are — I don't remember now if it’s 50 or over, 55 and over who’ve had that shot. Is it fair to compare it to something like that?

Dr. Hana El Sahly: Indeed. It is fair. However, the only difference is that with Shingrix, we see this reaction after dose one or after dose two. Here it seemed to be more predictable after dose two. But yes, that’s a fair comparison.

Jamie DePolo: Okay. Okay. Great. Now, here’s also another big question from our Community: If someone gets vaccinated — they’ve had both of their doses, not just the first dose, but both doses — does that person still need to wear a mask and maintain physical distance from other people? And I guess, kind of the flipside of that is: Could that person still infect someone?

Dr. Hana El Sahly: Great question. Both studies, the Pfizer and the Moderna, have demonstrated that these vaccines prevent disease in the short term — meaning symptomatic disease with fever or cough, shortness of breath, these illnesses caused by COVID. What we don’t know is the effect of these vaccines’ asymptomatic infection — meaning people can have the virus replicating in their upper airways without knowing, or having no to little symptoms. We do not know that these vaccines prevent the asymptomatic state. So it is advisable that, even after getting those vaccines, to continue social distancing. In the long run, we can imagine a large fraction of our population having had the vaccine and herd immunity developing — hopefully by vaccines and not infection — then there will be newer or different guidances pertaining to relaxing these social distancing recommendations.

Jamie DePolo: Okay, and do we know how long immunity — or I shouldn’t say “immunity” — but protection from the vaccine lasts? I’m wondering, would somebody need to get another vaccine in say 5, 10, 20 years?

Dr. Hana El Sahly: That is unknown. At this point, both vaccines were only granted emergency use authorization based on short-term data. The efficacy of these vaccine will continue to be examined for the long run to allow a determination of the long-term efficacy, and then we can have more informed recommendations regarding potentially how long the efficacy lasts.

Jamie DePolo: Okay. Now, if someone knows they’ve been infected with COVID-19, should that person still get the vaccine?

Dr. Hana El Sahly: It is not known how long after an infection a person is protected. We do know that the infections are really rare in the first 90 days. So, these individuals, if they are in a high-risk category — meaning they are healthcare professionals, or they are in the essential personnel group — it is recommended that they still get their vaccine. As a corollary to that, get their vaccines not when they are sick with COVID, but sometime later. They are not prioritized to get the vaccine, of course. And scarcity, let’s say — it’s probably better to give the — if there’s one dose left — to give it to someone who has not had COVID. But they are not excluded for sure; they can go and get the vaccine if they are in a priority group.

Jamie DePolo: Okay. Okay, and then, I’m curious, too: There have been stories in the news about a mutant strain of COVID-19 in the United Kingdom. I’m guessing we don’t have any data? But, I’m going to ask you the question anyway, because I’d rather have an expert say this than me, guessing: Do we know if the vaccines are effective on this strain? Do we have a sense that it might help? Or do we have any data at all?

Dr. Hana El Sahly: We don’t have data at all. All we know is that this strain sort of took over in the U.K., and it replaced a previous strain in a good portion of the United Kingdom sometime between September and now. We do not know that this virus is any worse in terms of it causing illness, and we do not know whether it’s more transmissible or replicates more in the airways than the other one. So, a lot of it is unknown. All we know is that it replaced the previous strain — or it became more prevalent — in the southern United Kingdom. I hear that — and I actually I read that — there’s a similar story taking place now in South Africa, without this virus showing that it is particularly causing more people to land in the hospital, for example.

Whether the vaccine works against these emerging strains is under intense research right now, and a proxy — or way of sort of gauging that — is by checking if the antibodies mounted against the common strains neutralized this virus in the lab. So, last time I checked, I looked for these data — they’re not out there — but this is the next step that will help us gauge whether the vaccines and the other modalities work against this virus, [or] viruses.

Jamie DePolo: Okay. Thank you. And to wrap up, I know that states are really deciding who gets the vaccines and when, and healthcare workers and people in long-term care facilities are the priority. They’re the first in line. I have read that older people — people 65 and older — and people with medical conditions that put them at high risk for COVID or severe COVID complications would be next. And I also know that this all depends on how much vaccine is available. So, this is a very long way of asking: Do you have any sense when people who’ve been treated for cancer might be able to get vaccinated? You know, are we thinking beginning of 2021, maybe mid — or would they be, like, the next group in line?

Dr. Hana El Sahly: It varies by state. In Texas, for example, individuals older than 65 or individuals with underlying medical condition of any age, including cancer, are sort of — they’ve been moved up the line, so to speak. So, they may get it faster. That is, again, under debate right now. But, as you mentioned, it is up to the states to sort of roll out the vaccine to those populations recommended by the ACIP. Most everyone prioritized healthcare workers. I know in New York, the long-term care residents are 1b, but essential personnels were moved up along with the healthcare personnel. So, it varies by state. 

But my best guess is that individuals older than 65 or those with underlying comorbidities, including cancer, will likely get it in early 2021. In the meantime, infection prevention works. Masks, frequent handwashing, keep your distance from others, do prevent the illness — the infection, and hence the illness. So, if more of us abide by these measures, it would be efficient as well.

Jamie DePolo: Thank you so much, Dr. El Sahly. I really appreciate your insights on this topic.

Dr. Hana El Sahly: Well, thank you for having me, and let me know if you have other questions.

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