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During the 2022-2023 respiratory season, the bivalent COVID vaccines had an effectiveness of 54% against infection and 49% against symptomatic COVID in children and adolescents ages 5 to 17 years, a new study in showed.

In this interview, Melissa Briggs Hagen, MD, MPH, of the CDC's Coronavirus and Other Respiratory Viruses Division, discusses the data.

The following is a transcript of her remarks:

This study was designed to assess how well the bivalent vaccine protected children from infection -- both general SARS-CoV-2 infection and symptomatic illness -- during the last respiratory virus season.

For this study, the groups that we were really assessing were those who had received the bivalent vaccine and those who had not. Those who had not received the bivalent vaccine may have received the monovalent vaccine or may have had prior infection, so they weren't completely non-immune, but they hadn't received the bivalent. Those were our two comparator groups.

This study did show that among the almost 3,000 children from the six different sites that were enrolled and monitored that the bivalent vaccine protected against all infections with an effectiveness of 54%, and was 49% effective at protecting them from COVID-19 illness or symptomatic infection.

We did, in the study, stratify by age and look at those who were 5 to 11 versus 12 to 17. We also stratified by history of prior infection, as that's been a big question -- how well the vaccine works if you've been previously infected. So we separately looked at those who'd been infected in the past and those who had not. Then we also looked within a specific subset of people who were from the largest site, because we wanted to make sure there wasn't any kind of bias based on our different sites and the different vaccine uptake.

Every different way that we sliced this, we found that the vaccine was effective in preventing infection, both overall infection and symptomatic infection.

We think it's important because the bivalent vaccine did provide protection against infection during a time period in which Omicron and some very, very transmissible sublineages of Omicron were circulating. So, this wasn't completely known.

We've had a lot of studies that have shown that COVID-19 vaccination in general works to prevent severe disease. That is the main goal of the vaccination program, and so many of the studies that come out are really looking at medically-attended outcomes such as urgent care visits, emergency department visits, hospitalization. Those are both easier to study -- because you can do a case-control design or a test-negative design -- and they're also more what's driving the vaccine policy. Many of the studies that have come out have been focused on those outcomes.

There have been some studies on the outcomes that we looked at -- these milder outcomes like infection and like symptomatic illness -- but not specifically in school-aged children and during this timeframe of the bivalent vaccine being available and all of these new sublineages of Omicron circulating. So, we thought it was important to analyze it.

We also thought it was important that we do it with this very rigorous study design. We knew that we didn't miss any infections. We were swabbing weekly, there was very high compliance -- over 90% throughout the study period -- and then we also had antibody tests at the start of the study to know if they were prior-infected. So we really had a lot of data in this study to understand well how the vaccine was working.

This was not a study that looked specifically at the latest vaccine. The 2023/2024 monovalent vaccine that's now been released and is available for people to receive today is being studied at CDC. CDC just recently put out an MMWR [Morbidity and Mortality Weekly Report] last week that found very similar findings to what we found. It was looking at symptomatic illness and testing positive for COVID-19, and it was 54% protection against infection in that study as well. So we think that's very encouraging that we're continuing to see the vaccine work even as new variants arise, including the new JN.1 variant.

Still, uptake of the vaccine is quite low. Perhaps families, parents, providers feel like they're not at risk for severe disease or they're not at risk for the outcomes that the vaccine is really targeting.

But we know that COVID-19 infection is very common in children, that it does result in a lot of missed school and a lot of parents having to take off work, and potentially transmission to more susceptible, older adults. So the fact that the vaccine does work against this milder outcome, I think, is relevant. I think it's an important tool for families and for providers and for policymakers to be aware of.

The last thing I would say is that the current COVID-19 season is still quite high-circulation in lots of parts of the country and the current vaccine is still available. I would encourage you to read the study, to evaluate it for yourself. We, again, believe that it's really well-designed, and it's information that you can stand on when talking to your patients or informing other members of the public what the benefits are of this vaccine.

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