Medical Examiner

Will Kids Vaccines Get the Pandemic in Check?

A tour through what the research says on transmission of the virus among the vaccinated.

Three kids in backpacks walk down a sidewalk toward a parking lot.
François Picard/AFP via Getty Images

Kids vaccines are finally here. Earlier this month, the Center for Disease Control and Prevention recommended that children aged 5 to 11 be vaccinated against COVID-19. The American Academy of Pediatricians supports the vaccine, given that this year, COVID has been in the top 10 causes of deaths for kids. Chicago and New York are each offering kids $100 if they get vaccinated (in a gift card or debit card, respectively). Some puppets on Sesame Street even “got” their doses to encourage young kids to do the same.

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The data is clear: The COVID vaccine will protect kids and is very, very safe. But it’s unclear to what extent vaccinating young kids will make us all safer. To be sure, the more vaccinations, the better. But with politically divisive pediatric mandates on the horizon, and many of us trying to get some sense of what our second COVID winter will look like, it’s worth asking: How much will vaccinating kids actually reduce spread?

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It may come as no surprise that the data isn’t as precise as we might like, so I spoke to a few experts to sort out what we know about kids, vaccines, and transmission—and what the implications are for policy.

I am, to be honest, still slightly unclear how often kids get COVID in the first place.

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It’s been a confusing ride. Early in the pandemic, “there was this misperception that kids didn’t get COVID, and they couldn’t transmit COVID,” said Dr. Melissa Stockwell, chief of the division of child and adolescent health at the Columbia University Irving Medical Center. But during that time, schools were shut down and many parents were working from home. Many kids were simply not exposed to the virus, explains Stockwell, which made them appear to be somewhat immune to harboring it.

Researchers know better now. Kids are just as likely to carry the virus as adults according to a (pre-delta) study that Stockwell did in collaboration with the CDC, University of Utah, and Abt Associates. Their work lines up with more recent epidemiological data from the U.K. showing that the prevalence of infections in schoolchildren under 12 was nearly twice the national prevalence. In the U.S., as of Nov. 4, there have been 6.5 million known infections in children, and almost a quarter of all positive cases are currently in kids. “I think we can say with complete certainty that children do get infected,” Stockwell said.

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OK, we know they get infected. But I heard they carry less virus, so they are less likely to transmit it to other people?

The evidence on how much virus kids carry is mixed. Stockwell’s study found that young kids are asymptomatic 50 percent of the time (compared with 12 percent of the time in adults)—intuitively, you’d think that means they’d be less likely to transmit an infection. But some studies suggest that the amount of virus present in younger children’s noses—the viral load—is higher than that in adults or adolescents. Whether that translates to increased infectivity is a little unclear. But it’s possible that it does.

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So it’s actually totally unclear whether kids are more or less likely to transmit the virus vs adults.

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Biologically speaking, yes, it is unclear. But there’s more to whether you’ll spread a virus than how much of it you have in your body.

One very important fact to add to the mix: remember that younger kids can’t isolate when they are infected. They need to be held, comforted, and cared for. You can’t really social-distance from your sick 3 year old.

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Right.

All the viral load stuff aside, we do have direct evidence that kids can drive outbreaks. A Canadian study published in August found 6,000 households in Ontario with pediatric index cases—that is, instances in which a kid brought the virus into a home. They found that other members of the household became infected about a quarter of the time. When the virus did spread, typically two other household members would become infected. Children aged 4 to 13 were just as likely to transmit as older teenagers—in line with systematic review of all studies on the topic.

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There’s a recent example that’s more dramatic. A Chinese study posted on a preprint server on Monday painstakingly traced how two young school-age kids seeded an outbreak involving at least 223 people. The virus was transmitted mostly through schools, factories, and households. Of the cases, 132 were fully vaccinated teens and adults (with the Sinovac or Sinopharm vaccine), and six of the cases ended up being severe or life-threatening. The authors concluded children were “critical hidden spreaders” in this instance.

Whew! That is a lot. What is the bottom line on kids and spread?

Contrary to what we thought at the pandemic’s onset in the U.S., it’s now looking like kids catch and transmit the coronavirus about as much as adults and adolescents.

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Well, vaccination will fix this, I assume?

Yes. In the long run, vaccination in all groups will drive down case rates and make everything less COVID-y (more on that below). In the short run, a vaccinated kid will make your household a little safer.

And remember: Getting the vaccine will make your kid safer from any bad outcomes of the virus, which in kids, are somewhat rare anyway. Large-scale observational studies in adults suggest the vaccines’ effectiveness against bad outcomes remains reasonably high—from 73 to 98 percent, depending on the vaccine and the details of the study—even as protection against infection declines in the era of delta and waning antibodies.

Right. Right. They should get vaccinated. To what extent will them getting vaccinated prevent them from potentially bringing the virus home?

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Once the virus enters the home, being vaccinated helps, but it could matter less than you might think. So, say your kid gets the virus—that could still mean that your family is going to have to worry a bit about getting sick as a whole.

Both a Dutch study and a U.K. study, recently posted as preprints, came to similar conclusions: In teens and adults, vaccination lowers an infected person’s chances of spreading delta to housemates by at least 50 percent. Being vaccinated (with Pfizer) reduced the chance of catching it from a housemate by 67 percent, according to the U.K. study. Pretty good—but there’s a big caveat. Those percentages were almost halved just three months post-vaccine. Another smaller but more detailed household contact tracing study paints an even starker picture. About a quarter of all household members ended up with an infection whether or not the originally infected person was fully vaccinated. On the receiving end, vaccination reduced a household member’s risk of catching the virus from 38 percent to 25 percent, but this trend didn’t reach statistical significance.

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Sure sounds like you are saying that the vaccine doesn’t really prevent spread!

No, that’s not what I am trying to say. First, all studies above find some evidence that the vaccine is protective against household spread—just not as much as we’d hoped. Second, epidemiological data show that, overall, vaccinated people have much lower rates of COVID. That is, a vaccinated person is just less likely to get the virus in the first place. So yes, if the virus gets into your house, you have a decent chance of getting infected. However, vaccination means it’s less likely the virus will ever arrive on your doorstep.

I am confused.

It might seem contradictory that vaccines significantly lower the chance of catching the virus yet are only somewhat able to prevent spread within the house. Stockwell, the Columbia University pediatrician, pointed out one way to square these two facts: The house and the rest of the world are very different places—in the home, you have prolonged exposure in small, enclosed spaces. In other words, the perfect conditions for spread. Outside the house, exposure might be more transient, or depending on where you live or what you’re doing, you might be masked up. At the community level, these small differences start to add up, meaning vaccination appreciably reduces overall spread.

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At the population level, what kind of impact will kids getting the vaccine have? Will cases go down as kids get vaccinated?

The short answer is yes, though it is very difficult to say by how much (and if you’re trying to figure out your winter plans right now, know that there are so many other factors involved).

The CDC estimates that vaccinating half of all children 5- to 11-years old could prevent a cumulative 600,000 cases between now and March 2022. I spoke to Dr. Luke Mullany, a biostatistician and epidemiologist at the Johns Hopkins Applied Physics Laboratory, who provided the numbers for the CDC. According to this estimate, averting 600,000 cases would avert 50,000 hospitalizations and 10,000 deaths. Models he analyzed on behalf of the Scenario Modeling Hub assumed vaccine uptake among 5- to 11-year-olds would be similar to uptake among 12- to 17-year-olds, which gives a ballpark estimate of about 1 preventable death per 1,300 childhood vaccinations. Given that the vaccine risks to children are vanishingly small, these numbers make a reasonable case for immunizing kids to save the lives of others.

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That’s great, that sounds like a very dramatic reduction of cases and deaths.

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Yes, it is. But that’s still assuming half of kids get vaccinated, which is not a sure thing. “I know that Dr. Fauci has said this [pediatric vaccine authorization] is a game changer,” said Dr. William Raszka, director of pediatric infectious diseases at the University of Vermont Children’s Hospital and a professor of pediatrics at the Larner College of Medicine. “But I am not nearly as sanguine as most of my peers that immunizing children 5 to 11 is going to dramatically decrease the number of infections.”

The reason, he said, is that only 1 in 3 parents plan to vaccinate their children. The impact of those unvaccinated kids will probably be borne by communities with lower vaccination rates overall, continuing to put the brunt of COVID unevenly on some Americans. “Adults who have not immunized themselves seem really unlikely to me to immunize their 5- to 11-year-olds,” said Raszka. “I just don’t think that’s really going to change.” And because the adults in those communities are unvaccinated, pediatric transmission could result in far worse outcomes than just passing along an infection.

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It seems like some of that could be avoided by mandating the vaccine for kids.

Some jurisdictions are trying. Within 24 hours of the CDC’s decision, the San Francisco Department of Public Health announced that schoolchildren would have to comply with the city’s strict proof-of-vaccination requirement to enter public spaces such as restaurants. It’s possible that other cities will follow suit. It may only be a matter of time before some schools mandate the vaccine for this age group.

Broader statewide mandates, however, could be politically tricky. COVID vaccine mandates, if you haven’t heard, are extremely divisive. And anything to do with schoolchildren is not only emotionally charged but also a politically potent tool. People are resentful with many schools for mishandling the pandemic—the delayed reopenings and evidence-free policies have profoundly disrupted the lives of children and parents alike. In the Virginia governor race, Republicans found a receptive audience for anti-school messaging of all stripes. Mixing mandates and children is bound to be explosive.

Update Nov. 13, 2021: This piece has been updated to better reflect Dr. Luke Mullany’s credentials.

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