COVID-19 vaccine effectiveness in children dropped during Omicron wave, increased with booster

The effectiveness of COVID-19 vaccines declined rapidly in children and adolescents during the Omicron wave and increased after a booster dose, a new study finds.

The study, published in JAMAanalyzed 121,952 SARS-CoV-2 tests administered at 6,897 pharmacy drive-through testing sites between December 26, 2021 and February 21, when the Omicron variant was circulating widely.

“When the Omicron variant became dominant, the protection against symptomatic COVID-19 provided by the primary series (2 doses) of the Pfizer-BioNTech mRNA vaccine fell in children and even more so in adolescents within two months of the vaccine. second dose,” Katherine Fleming-Dutra, MD, of the Centers for Disease Control and Prevention, said Contagion. “A booster significantly improved protection in adolescents. This new study supports recommendations that parents should keep their children informed of all recommended doses, including boosters for teenagers.

The results are consistent with previous research in adults, showing that COVID-19 vaccines were less protective against symptomatic infection of 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, of which 22,273 tested positive, from children aged 12 to 15. At 2 to 4 weeks after the second dose, vaccine efficacy against symptomatic infection was 60.1% among the younger cohort and 59.5% among the older group. During month 2 after the second dose, vaccine efficacy had dropped to 28.9% and 16.6% respectively. Among adolescents who received a booster dose, vaccine effectiveness increased to 71.1% two to 6.5 weeks after the booster dose.

“Our results weren’t 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 seen in adults with AD. ‘a variant of Omicron infection, including that of the same test platform, after receiving a second dose of a primary series of vaccinations,’ Fleming-Dutra said. children, adolescents and adults shows us that vaccines offer the same protection in children as in adults, and the lower than expected efficacy of the vaccine against symptomatic infection is due to reduced protection against Omicron variant.”

Emergency use authorization was granted in May 2021 for COVID-19 vaccines for children aged 12-15 and in October 2021 for a lower dose of the vaccine for children aged 5-11. .

The FDA approved booster doses for children ages 5 to 11 this month, after previous research showed a 36-fold increase in neutralizing titers of Omicron after a third dose of their COVID-19 vaccine. Teen boosters were approved in January.

“The study did not assess the health status of these children during the tests; however, because these children were tested for COVID-19 at drive-through testing sites without seeing a doctor, they most likely had mild illness,” Fleming-Dutra said. ” This mean that vaccination does not work to prevent serious illness and hospitalization. Vaccination protects against serious illness and hospitalization. We know from other studies that staying up to date with COVID-19 vaccinations, 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 becoming increasingly common. They also noted that the estimated vaccine effectiveness against severe illness and hospitalization was higher and declined more slowly than that of symptomatic infection.

“The CDC is focused on preventing serious illness, hospitalizations, and deaths from COVID-19 and monitoring data that informs about these things. But the CDC will also continue to monitor the vaccine’s effectiveness against mild illnesses, as it did in this study, because these results can serve as a signal,” Fleming-Dutra said. “If, for example, we see an increase in milder symptoms of COVID-19 along with a corresponding decline in vaccine effectiveness in people with milder symptoms, that could give us a signal that we should study the possible increases in serious illness and decrease in vaccine effectiveness against this.”

Sara H. Byrd