COVID-19 Vaccine Effectiveness Among Children Dropped During Omicron Wave, Increased with Booster

Effectiveness of COVID-19 vaccines decreased rapidly among children and adolescents during the Omicron wave and increased after a booster dose, a new study found.

Thestudy, published in JAMA,analyzed 121,952 SARS-CoV-2 tests administered at 6897 pharmacy-based, drive-through testing sites between Dec. 26, 2021 and Feb. 21, when the Omicron variant was widely circulating.

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

The results are consistent with previous research in adults, showing COVID-19vaccines were less protective against symptomatic infection from the Omicron variant than the Delta variant.

The study included 74,208 SARS-CoV-2 tests, 30,999 of which were positive, from children ages 5-11 and 47,744, including 22,273 positive tests, from children ages 12-15. At 2 to 4 weeks after the second dose, vaccine effectiveness 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 effectiveness had dropped to 28.9% and 16.6% respectively. Among adolescents who received aboostershot,vaccine effectiveness rose to71.1% two to 6.5 weeks after the booster.

“Our results were not really surprising, but it was very striking how similar the drop-off inprotection in children and adolescents that we found in this study was to the drop-off in protection seen in adults with Omicron variant infection, including one from the same testing platform, after they received a second dose of a primary series of vaccinations,” Fleming-Dutra said. “This finding of such similar results among children, adolescents, and adults demonstrates to us that vaccines are providing the similar protection in children as they do in adults, and the lower than expected vaccine effectiveness against symptomatic infection is due to decreased protection against the Omicron variant.”

Emergency Use Authorization was granted in May 2021 for COVID-19 vaccines for children ages 12-15 and in October 2021 fora lower dose of the vaccine for children ages 5-11.

The FDA approved booster doses for kids 5-11 this month, after previous research showed a 36-fold increase in Omicron neutralizing titers following a third dose of their COVID-19 vaccine. Booster for adolescents were approved in January.

“The study did not assess how ill these children were at testing; however, because these childrenwere being tested for COVID-19 at drive-through testing sites without seeing a doctor, mostlikely had mild illness,” Fleming-Dutra said. “This does not mean that vaccination doesn’t work to prevent severe disease and hospitalization. Vaccination does protect against severe disease and hospitalization. We know from other studies that staying up to date with COVID-19 vaccinations, including booster doses for those eligible, offers the best protection against severeillness, hospitalization, and death.”

The study authors noted that prior infection could affect the estimates of vaccine effectiveness and is becoming more common. They also noted that estimated vaccine effectiveness against severe disease and hospitalization has been higher and waned more slowly than that of symptomatic infection.

“CDC focuses on the prevention of severe illness, hospitalization, and death from COVID-19 and monitors data that inform on these things. But CDC will also continue to monitor vaccine effectiveness against mild illness—as it has in this study—because those findings can serve as a signal,” Fleming-Dutra said. “If, for example, we see an increase in milder COVID-19 symptoms along with a corresponding drop in vaccine effectiveness in people with milder symptoms, that could give us a signal that we should study possible increases in severe disease and waning vaccine effectiveness against it.”