Last week, the first kids under 5 were vaccinated against COVID. Not surprisingly, I have followed this closely: the chaos leading up to approvals, the approvals in various stages almost two weeks ago, the data, the rollout. I’ve done polls of vaccine intentions on Instagram, and I’ve read countless emails and DMs from parents who are excited but also those who are confused, hesitant, unsure. I’ve read all of the public health messaging (or, well, a lot of it).

At the end of this processing and reading, I felt very … frustrated. As I reflected on it more, I realized this frustration was not dissimilar to some of the frustrations I felt during pregnancy.

Let’s take deli meats. The general advice is not to have them during pregnancy. That advice, however, varies across practitioners, across books, and across countries. When I was first pregnant, I found myself wondering why these were restricted. Was it the same reason as raw oysters? Was prosciutto a deli meat?

Obviously, COVID vaccines for kids are both more fraught and more important than a turkey sandwich (although my pregnant self might have disagreed). But it has some of the same feeling. There is public health advice from the CDC: vaccinate your child as soon as you can with whatever vaccine is available.

But this is, frankly, at odds with what a lot of people are hearing from their pediatricians, who in many cases are encouraging people to wait, especially if their child recently had COVID. Moreover, the public health advice hasn’t engaged specifically with many of the detailed questions parents have. Questions like: Which vaccine? If my child is almost 5, should I wait for a bigger dose? What if they just had COVID?

You can find specific answers to some of these below, but just as with the deli meats, I realized as I thought about this that answering specific questions isn’t really enough. To serve what people need, we have to step back and give people a framework for understanding why and how the vaccines work.

I’m going to try to do that today. I also want to be clear: My focus in this post is not on convincing people to vaccinate. Instead, I want to help people navigate the details of their vaccine planning in a way that works for them.

In most cases, vaccines are going to be delivered through your pediatrician’s office. In the end, this means that they should be the ultimate source for helping make decisions about which vaccine and when. My hope is that — as with my writing on pregnancy — this framework will give you a better place to start the conversation.

Understanding the point of vaccines

The primary goal of vaccinating children under 5 is to generate some protection against COVID-19 by priming their immune system to respond to the virus if it encounters it in the wild. This will lower susceptibility to illness and likely make any illness that does occur more limited.

That’s the two-sentence version. But to dig into what this reasoning implies about the timing of vaccines, prior infection, and so on, we need to say more about how vaccines work.

A three-point vaccine framework

First: What does the vaccine do? The vaccines for COVID-19 induce your body to produce antibodies against the viral spike protein. They also train other parts of your immune system (T cells and B cells) to be ready to fight the virus. This is similar to what happens when you become sick with COVID-19. A major difference is that the vaccine induces the antibodies by introducing only a part of the virus, so it does not give you the disease.

Vaccination before disease has both short- and long-term effects. In the short term, your body has antibodies to the virus that’s circulating around. This puts it in a good position to prevent illness altogether, because the antibodies are right there. This protection wanes over time and is diminished when faced with new variants. In the longer term, however, your body retains T-cell and B-cell memory, which gives it much more robust protection against serious illness and death, even with new viral variants.

We have seen in study after study that the most robust longer-term protection provided by the COVID-19 vaccines is against serious illness and death. There is some short-term protection against illness, but it isn’t as good and it deteriorates more quickly.

Second: How do we think about boosters, infection, a combination of infection and vaccination, etc.? Each of these events are a further immune system primer. When you get a second dose, or a booster dose, of the vaccine, it further stimulates the immune system. This provokes both more immediate antibodies and a more robust T-cell and B-cell response. In the short term, a booster effectively re-ups your ability to fight off immediate infection. But it also shores up the secondary immune system response, so the response to later exposure is also better.

Infection with COVID-19 after vaccination (or after prior infection) also serves as an immune system booster. Exposure to the virus itself produces antibodies to a broader set of viral proteins. In addition, COVID-19 infection may help develop another layer of immunity through your mucous membranes. This mucosal immunity helps prevent reinfection by attacking the virus at the point of entry (nose/mouth) before it has a chance to invade cells. Both factors mean that “hybrid immunity” produced by both vaccination and infection, in either order, is more robust than either alone.

The timing of vaccine doses matters. Giving two vaccine doses one day apart wouldn’t help much, since they would provoke a single (very large) immune response. So multiple doses, or boosters, should come at some distance — in fact, the longer the interval, the better the quality of the antibody response.

Third: Why does dose size matter? The goal of vaccination is to produce a response from the immune system that is sufficient to provide protection against the virus but does so with relatively minimal side effects. A huge dose of vaccine that really overloads the system would produce a very significant antibody response, but at the cost of making the host very sick. This is by no means a perfect correlation, but overall a larger dose of vaccine will produce more antibodies but also more side effects. There is also an interaction with age — adults need larger doses for similar protection, partly due to size and partly to the functioning of their immune system.

Answering questions

In my view, if we keep these three points in mind, it can help answer a lot of key questions. Some examples…

Why do we see a difference between Moderna and Pfizer for the under-5 set? Moderna generated a large antibody response after only two doses; Pfizer needed three. This is because (point #3) vaccine dose matters, and Moderna has a larger dose. It is also the reason that the side effects of Moderna seem to be worse (also point #3). And point #2 helps us see why a third dose of Pfizer would be sufficient to generate a large response.

How should prior infection affect my vaccination decision? You can think of a COVID infection as, basically, a first dose or a booster (see point #2). Better protection is provided by multiple doses, which is why vaccination is recommended even for children who have had COVID. But it’s also the case that multiple doses are more effective with more time between them. So if your child just had COVID last week, it likely makes sense to wait.

If my kid had COVID, should I wait for the next surge to vaccinate? Maybe. Of course, exposure can happen outside of a surge, too. But it’s certainly the case that protection against infection is strongest right after vaccination (point #1), and prior infection is already quite protective against serious illness (point #2). Similar to how we deliver flu vaccines near the winter surge, there is logic to this, especially if your child has had COVID.

Your questions might not be these! But the framework can help, even if your questions differ.

A final point: risk of death

Before closing, I want to address what I think is a large failure of public health messaging, which is the continual focus on the risk of death for children as a vaccine motivator.

Last week, there was a report out of the U.K. that detailed the extremely low risk of death for children from COVID-19 (see a long discussion of the study here). This was reassuring, and it reinforced a fact that we have known since the start of the pandemic: overall, and luckily, children are at very low risk for serious illness from COVID.

When I posted on Instagram about this, I got a number of messages asking, basically, what’s the point of vaccination if there is a low risk of death? The answer to this seems clear to me. We vaccinate kids all the time for things where the risk of death is extremely low. The most obvious parallel is the flu vaccine. Kids’ risk for serious illness or death from the flu is low, and the flu vaccine provides imperfect protection. But a large share of children are vaccinated every year, because parents know that the vaccine provides some protection.

This is all also true of the COVID-19 vaccine. Protection against illness is imperfect, but it’s better than the flu vaccine in many years. It seems extremely likely that it will lower infection severity even when people do get sick, even if they would not have been hospitalized.

The problem, I think, is that the public health messaging has emphasized the risk of death as a huge reason for the vaccination of kids. In the CDC’s Advisory Committee on Immunization Practices meeting, for example, some flawed data was presented in service of this, comparing deaths in the entire course of the COVID pandemic with yearly deaths from other illnesses, dramatically overstating the relative risk. It’s absolutely true and tragic that children have died of COVID. It is also very rare. But there are good reasons to vaccinate, even putting this aside. 

Frankly, it should be possible to encourage vaccination while also being clear that children are a low-risk group. And attempting to get people to vaccinate by scaring them, rather than by giving them the information they need to make good decisions, is not a way to build trust.