A new study found that the effectiveness of COVID-19 vaccines in children and adolescents decreased rapidly during the Omicron wave and increased after a booster dose.
The study, published in JAMAanalyzed 121,952 SARS-CoV-2 tests conducted at 6,897 drive-through test sites in pharmacies between December 26, 2021 and February 21, when the Omicron variant was widespread.
“As the Omicron variant became dominant, the protection against symptomatic COVID-19 conferred by the primary series (2 doses) of Pfizer-BioNTech mRNA vaccine declined in children and even more so in adolescents within two months of the second dose,” said Katherine Fleming-Dutra, MD, of the Centers for Disease Control and Prevention infection. “A booster vaccination has significantly improved the protection of young people. This new study supports recommendations that parents should keep their children up to date on all recommended doses, including adolescent booster shots.”
The results are consistent with previous research in adults showing that COVID-19 vaccines offer less protection against symptomatic infections caused by the Omicron variant than the Delta variant.
The study included 74,208 SARS-CoV-2 tests, of which 30,999 were positive, from children aged 5 to 11 and 47,744, including 22,273 positive tests, from children aged 12 to 15. 2 to 4 weeks after the second dose, vaccine efficacy against symptomatic infections was 60.1% in the younger cohort and 59.5% in the older group. By month 2 after the second dose, vaccine efficacy had decreased to 28.9% and 16.6%, respectively. In adolescents who received a booster dose, vaccine efficacy increased to 71.1% two to 6.5 weeks after the booster dose.
“Our results were not really surprising, but it was very striking how similar the drop in protection in children and adolescents that we found in this study was to the drop in protection observed in adults with an Omicron variant infection. including one from the same testing platform after receiving a second dose of a first series of vaccines,” Fleming-Dutra said. “This finding of such similar results in children, adolescents and adults tells us that vaccines provide similar protection in children as in adults, and the lower than expected vaccine efficacy against symptomatic infections is due to reduced protection against the omicron variant.”
The emergency authorization was granted in May 2021 for COVID-19 vaccines for children ages 12 to 15 and in October 2021 for a lower dose of the vaccine for children ages 5 to 11.
The FDA this month approved booster doses for children ages 5 to 11 after previous research showed a 36-fold increase in Omicron’s neutralizing titers after a third dose of their COVID-19 vaccine. Booster vaccination for adolescents has been approved January.
“The study did not assess how sick these children were when tested; However, because these children were tested for COVID-19 at drive-through testing sites without visiting a doctor, they most likely had mild illness,” Fleming-Dutra said. “It doesn’t means that vaccination does not help prevent serious illness and hospitalization. Vaccination protects against serious illnesses and hospital stays. We know from other studies that updating COVID-19 immunizations, including booster doses for those eligible, provides the best protection against serious illness, hospitalization and death.”
The study authors noted that prior infection could affect estimates of vaccine effectiveness and is more common. They also found that the vaccine’s estimated effectiveness against serious illness and hospitalization was higher and declined more slowly than that of symptomatic infection.
“CDC is focused on preventing major illnesses, hospitalizations and deaths from COVID-19 and monitors data that informs about these things. But the CDC will continue to monitor the vaccine’s effectiveness against mild illnesses — as it did in this study — because those results can serve as a signal,” Fleming-Dutra said. “For example, if we see an increase in milder COVID-19 symptoms along with a corresponding decrease in vaccine effectiveness in people with milder symptoms, that could give us a signal that we should investigate a possible increase in serious disease and a waning vaccine effectiveness there.”