Can We Spread COVID After Vaccination?

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Wear your mask. Or, don’t wear your mask if you are vaccinated, as long as you are outside. But, keep masking and social distancing inside even if you are vaccinated. It’s confusing to many.

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Vaccines have been proven to prevent serious infection, and studies that show a reduction in transmission are building, but they aren’t foolproof. A recent study by Public Health England found that a single dose of either the Pfizer-BioNTech or AstraZeneca vaccine reduced household transmission by up to half. Those both require two doses to be considered “fully vaccinated.” The study comes as we hear more about breakthrough COVID cases.

In this episode, Colleen Kelley, MD, an associate professor of infectious diseases at Emory University School of Medicine in Atlanta and a principal investigator for the Moderna and Novavax phase III clinical trials at the Ponce de Leon Clinical Research Site, joins us to explain the risk of transmission after vaccination.

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Following is a transcript:

Serena Marshall: Dr. Kelley, thanks for joining us here at Track the Vax. I want to ask you, just right off the bat here, what can I do once I’ve been vaccinated? Is it safe to, you know, give hugs, shake hands, work inside an office space? What’s the risk of transmissibility after COVID vaccination?

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Kelley: Well, from what we’ve seen so far, these vaccines are just as fantastic as we hoped they would be from the clinical trials with respect to the reduction in transmissions.

There have been several real-world studies, in the U.S., in Israel, in the U.K., that really show a profound reduction in asymptomatic infection and carriage after vaccination, particularly with the mRNA vaccines.

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We don’t have as much data yet with the Johnson & Johnson vaccine, but it also does look to significantly reduce transmission. So, I would say you can confidently go back to most activities. We still do want to be mindful in crowded spaces, in spaces with poor ventilation indoors.

We still want to be mindful of the very small possibility of transmissibility. But, in general, if you’re vaccinated, if your friends and family are vaccinated, life should look pretty much normal outside of crowded settings.

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Marshall: I want to dive into some of those studies you mentioned in just a minute, but real quick, let’s do a list check here. So if I’m vaccinated, my friends and family are vaccinated, can I shake their hand?

Kelley: Absolutely.

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Marshall: Give them a hug?

Kelley: Please do.

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Marshall: What about going to a communal workspace?

Kelley: I think going to a communal workspace is going to depend a lot on how many people are present, whether those folks are vaccinated or not. I think in healthcare where there are high rates of vaccination, we’re beginning to question some of this. Is it OK to go to the break room and have lunch with your colleagues (that we haven’t been doing for the last year) … and I think folks are beginning to understand that, yeah, that’s probably OK when all the parties are vaccinated.

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I think large meetings in an enclosed meeting room where not everyone might be vaccinated, I think those should still probably be delayed for the foreseeable future, or still be overlaid with distancing and masking as additional mitigation efforts.

But I think things are changing. And I think it depends on how small the place, the space you are going to be in, and how many people are going to be in that space.

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Marshall: Now a lot of folks might be hearing this, Dr. Kelley, and thinking: “Well, why did the CDC then stop short of saying, ditch the mask all together?”

Kelley: We’re just reaching those 50% vaccination levels that we want to see. And I think from a public health perspective, the message needs to be a little bit different than it does from an individual perspective. So if we’re telling a crowd where half the people we know are unvaccinated that only those people that are vaccinated should or should not wear masks, that’s a little bit more confusing and nuanced and may lead to some frustration among folks.

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When the public health message is “we still need to wear masks,” it’s very simple, very straightforward, and it’s something that we can all do to help us progress to end the pandemic.

Marshall: But what about the idea of still wearing a mask to protect those who aren’t vaccinated? I mean, we’re just talking about that crowd and you said, “Oh, well, 50% of those individuals likely aren’t vaccinated,” looking at the data. So if I have been vaccinated and I’m not transmitting, why do I still need to wear a mask then to protect those folks if breakthrough cases are so low?

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Kelley: Well, I think our understanding of that is evolving and you’re right. It may not be necessary for you to protect other people if you are fully vaccinated. I think a lot also depends on how much a virus is actually circulating in your community, as well. There are still pockets of the U.S. where there are high levels of circulation, and that’s where you’re going to see more breakthrough infections. In areas where there are very low levels of circulation, you may be right, there may be no utility to wearing that mask. But again, it’s a public health messaging versus an individual risk difference that we’re kind of threading the needle with, I think here.

Marshall: It’s a really delicate dance to be had…

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Kelley: Absolutely. It’s hard. If you think about it from a public health standpoint, trying to get a message out to the entire country that’s understandable and digestible and believable, something that says “if then, if then, if then,” is not going to fly. And I think that’s what CDC has been grappling with when we think about mask recommendations and vaccinated people.

Marshall: So, what about those breakthrough cases, though? We’ve heard a lot about people who still get COVID after the vaccine. So that might make them a little more cautious when it comes to, you know, going back into the office, even if everyone is vaccinated.

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Kelley: Yeah, absolutely. So breakthrough infections are occurring. They are extremely rare.

Marshall: When you say “extremely rare,” Dr. Kelley, what does that look like?

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Kelley: Well, so it’s less than, you know, 0.01%, so far, of people who have been vaccinated have been reported as having a breakthrough infection. We do not have very high levels of surveillance across the country to say with any certainty what number of breakthrough infections are occurring amongst all vaccinees, but it is a very, very, very small percentage of people who have been vaccinated.

What we do know is that those folks who do have those breakthrough infections, oftentimes they’re not symptomatic. And if they are symptomatic, it’s extremely mild symptoms that they’re experiencing. And so that means the vaccine worked exactly as we hoped it would, and that it turns COVID into a rare event. And when it does occur, it’s a very mild infection, something akin to a cold that people get or used to get every single year before masks were worn so widely.

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Marshall: So are those more likely happening in people who’ve only gotten one dose of the two-dose regimen or are those still happening in folks that are fully vaccinated?

Kelley: We would not consider the people who only got one dose as a breakthrough infection. A breakthrough infection is someone who’s fully vaccinated, meaning at least 2 weeks after their two-dose regimen if it’s an mRNA vaccine, or at least 2 weeks after the single-dose Johnson & Johnson vaccine.

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Marshall: So what about the breakthrough cases in the mRNA vaccines versus the J&J … is there a difference there?

Kelley: It might be possible that we will see that, but I’ve not seen any kind of head-to-head data comparisons to support that. But one might hypothesize that that will be the case, that you’ll see more breakthrough infections [with] the Johnson & Johnson vaccine, simply because we know that the efficacy estimates were slightly lower for symptomatic disease, even though that vaccine also had excellent protection against severe disease and death.

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Marshall: Dr. Kelley, I want to ask you again about that second dose. We know millions are skipping it because they’re worried about side effects. You explained why it’s necessary still to get the second shot, but what about cases where you get the first shot and then you get COVID? It’s not a breakthrough COVID case as you explained for us. But then do you still need the second shot, or is that second shot now like a booster shot?

Kelley: Yeah. I mean, in most cases, I would think of the second shot as a booster shot. I can’t speak exactly to the phenomenon of getting the first shot and then getting the infection and then getting the second shot, what the immunity looks like. But we certainly know that people who have had prior infection, and then get a first dose of the vaccine, do look very much like a very strong booster.

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We know that some people who get COVID infection, myself included, actually don’t respond — have a very strong immunologic response to the COVID infections, especially those who had mild infection, and so for those people, it is still very important that they get the vaccine.

Marshall: How does that timeline change, though?

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Kelley: For whether you got the infection after the first dose versus before?

Marshall: Yeah, between the first and second dose, you’ve gotten COVID. How does that timeline change?

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Kelley: Unclear, unfortunately. The recommendations right now are just to wait until you get better and go ahead and get that second dose. But I’m not sure that we have a good, clear understanding of what immunity looks like in that setting. I would say it’s probably pretty darn good, but that would be only a guess at this point.

Marshall: So, Dr. Kelley, we’ve talked about how you need that second dose for full efficacy of those trials. But we know the second dose brings you from around 80% after the first to around 90-95%, but J&J is only at about the 80s when it comes to efficacy. So someone might look at this and say, “Well, why do I need the second dose of Pfizer or Moderna if my efficacy is equivalent to a J&J one dose?”

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Kelley: So I think that 80% efficacy that has been thrown around for the first dose of the mRNA vaccines is a little bit of a misnomer. So those numbers have wide confidence intervals, meaning that it could be actually much lower or much higher. It varies quite a bit from study to study what the actual efficacy is after the single dose.

And because in most studies thus far, people get the second dose, and so efficacy after the first dose is only really measured at 3 weeks. It’s not really an accurate estimate of how much, how effective the vaccine is after a single dose for the long term. It’s really only a measure of how effective the vaccine is in the first 3 weeks after the first dose.

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So we would really need to follow people for a much longer period of time after that single dose, in order to be confident that they are protected at a significant level with a single dose of the mRNA vaccines. And I think based on the immune responses to the first dose that we know, I think most people would be fearful of doing something like that.

And there was a lot of controversy, especially when the vaccines were in such short supply, if we should only be giving that single dose. And I think in the U.S., they made the right decision of continuing on with the second dose on schedule that was done from the clinical trials at 3 weeks for the Pfizer vaccine or 4 weeks for the Moderna vaccine. Simply because we just didn’t know that answer. And we were really guessing. And when you’re guessing with immunity and breakthrough infections and transmissions and all of those things that were on the table, I think the safest course of action was to just continue to pursue that second dose on time. And now that vaccines are widely available, there’s really no reason not to get that second dose.

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Marshall: So let’s go back to some of those studies that you mentioned at the start. The one in Israel, for example, the U.K. had one, those are observational studies. So can we really say, based on that data, that those individuals aren’t transmitting the virus after vaccination?

Kelley: We cannot say anything definitively about them not transmitting. What we can say from those observational studies is that the risk of acquiring COVID, asymptomatic or symptomatic COVID disease, after vaccination is exceptionally low. And if that’s the case, then that also reduces their risk of transmission. The risk of transmission is exceptionally low because they don’t have it in the first place.

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The question about whether, you know, those are observational studies versus clinical trials, which, you know, in medical science is the gold standard — observational studies are not junk. They are very important and it’s incredibly important when we have multiple observational studies from multiple settings that are all showing the same thing. That’s pretty darn good data.

When we have [data] from different countries, from the healthcare setting, from outside the healthcare setting, all showing these significant reductions in symptomatic and asymptomatic disease after vaccination, that makes us more confident in that assumption.

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Marshall: You mentioned the healthcare settings, Dr. Kelley. That’s the CDC study you’re talking about. Is that applicable to the general population?

Kelley: I think probably … the CDC study was a bit small, but I still think applicable to the general population. Maybe one might say, “OK, well, healthcare setting folks are better at doing other mitigation efforts like masking, distancing, and that sort of thing.” And so that is important to know.

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There’s other studies that are ongoing. They’re trying to understand, in young people — people that may be less good at distancing and masking and that sort of thing, whether we’re going to see the same results. And as we continue to see, you know, in Israel they first rolled out the vaccine just as we did here in the U.S. to the healthcare workers and the elderly, and then came down and down and down into lower and lower age levels. And we’re seeing the same thing as they showed in the older age groups and in healthcare workers. So I think that additional data will accrue. And I’m fairly confident it will show the same thing: that [transmission] in asymptomatic and symptomatic disease is incredibly rare after vaccination.

Marshall: It’s incredibly rare after vaccination, but what about those with unvaccinated family members at home? Like their kids or maybe somebody who is high risk and unable to get a vaccine?

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Kelley: Yeah. And so that is a situation where you may see those breakthrough infections. If someone is in a household of people that are not vaccinated or unable to be vaccinated, and one of them were to acquire COVID and they would have a significant exposure in the household, meaning, you know, with them constantly. That may be a case where you see that asymptomatic or mildly symptomatic breakthrough infection, but that person, to date we’ve seen, should still be very confidently not hospitalized and not die from their COVID infection. And so that’s great news.

Marshall: But what if they’re worried about passing that on to that family member? Not getting it from the family member.

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Kelley: So passing it on to someone who’s maybe immunocompromised in the household?

Marshall: Or even a kid. I mean, we’re not vaccinating those younger than 16 at this point. [Editor’s note: Just after the interview, the FDA authorized Pfizer’s vaccine for children ages 12 to 15.]

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Kelley: Yeah. I would say that’s also going to be a very rare event. I think we probably need some additional information to say absolutely that those folks are protected. In general, I would say that’s going to be a very rare event.

We also need to learn a little bit more, for those folks that do have those breakthrough infections, what their viral load looks like. How much virus they’re actually carrying and shedding. And I suspect it’s going to be, for most people with a breakthrough infection, really low compared to those who had symptomatic disease before vaccination, who likely probably had much higher viral loads, and the viral load certainly is going to correlate with transmissibility. And so those are some additional data that we’re waiting on.

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Marshall: But you said it’s going to be very low, that someone who’s vaccinated could pass it on to an unvaccinated child. Folks might be listening to this and say, “Well, we’re seeing new variants, they’re coming out and they’re more highly virulent,” so what about those situations?

Kelley: Well, I mean, so far so good with the variants. It does appear that the B.1.1.7 variant, which is now the majority variant in the U.S., the one that was first identified in the U.K., does appear to be still very vaccine-sensitive. I think that’s what we’re learning is, are these breakthrough infections occurring with the wild-type virus versus the variant viruses.

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I think those are all things that we still have to learn. And I think it’s something that we’re very attentive to. But again, I would say, so far so good. The vaccines seem to be holding up extremely well.

Marshall: But “so far so good” might not give a lot of people who are concerned the same level of confidence in that variant transmission. So, at some point, is there a concern that those vaccines could be rendered useless by certain variants, that transmissibility could come back?

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Kelley: I think that’s a fear, but is not founded thus far in any real data. You know, the last year and several months at this point of COVID have been an uncomfortable place for all of us to be in because we don’t have all the answers we want right now. We’ve had to wait. We’ve had to wait and see on many fronts. We’ve had to make our best guesses about a lot of things and sometimes we’ve been wrong. Usually we’ve been right, I think, in general, folks in the scientific and public health community who overall have had to make their best guesses based on the data so far.

And the data so far we have is quite extensive, and I would say that it’s unlikely that the vaccines will be rendered completely useless. Over time, we’re going to have to watch very carefully what happens in places like India and Brazil and other countries in South America that have just had completely out-of-control transmission ongoing. And what that does is lead to variant production. And so time will tell what happens in those countries with those outbreaks and production of potential new variants. But we have to sit with our discomfort right now. Be confident in our vaccines, and wait to see what transpires in the coming months.

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Marshall: And let’s talk about really quickly, Dr. Kelley, a different kind of transmission — of antibodies, mothers to newborns. Those who were pregnant or in breast milk. We’re learning more about that, about the COVID antibodies when it comes to that kind of transmissibility. And that’s a good one, right?

Kelley: Yeah. I mean, so far, early on, people were worried that it didn’t look like antibodies post natural infections were being transferred to the baby, but now it seems like it does look like there is some transfer to infants. I think that’s what everyone thought would be the case. Because we know that from influenza and influenza vaccinations that babies of moms that got vaccinated for influenza are protected.

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And so I think one might assume the same might be true for COVID, as well. So that also is something we’re studying. That’s also something we’re going to learn more about. How the vaccine protection is transmitted to babies, how long it lasts, how good it is, etc.

So again, that’s one of those things we will be anxiously awaiting the results from the scientific studies. Again, though, COVID infection in young babies is extremely rare and they tend to do very well if they do acquire COVID disease or infection. So that’s all good news and all pointing to a positive outlook for babies.

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Marshall: Dr. Kelley, bottom line here — it sounds like when it comes to transmissibility, if you’re fully vaccinated, you’re pretty good to go.

Kelley: I agree with you. You’re pretty good to go. I think we still have to do our part from a public health perspective and still be masking, still be avoiding crowds, still not having folks gathered together in settings that are not safe, which is crowds that are a mix of people, both vaccinated and unvaccinated, just from a public health perspective.

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But I think on the individual level, yes, absolutely. You are good to go.

Marshall: You could have that family barbecue with your immediate family and a couple of friends who are all fully vaccinated, even if the kids aren’t?

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Kelley: Yeah, I do. That’s what my family’s doing. That’s what we’ve decided … that the risk is low enough that we are willing to accept that to socialize with our vaccinated family and friends, even though the kids are not yet vaccinated. That’s a risk we’ve been willing to take!

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