Protection from COVID-19 booster lasts at least 3 months in children, study finds

Protection against the omicron variant from the Pfizer-BioNTech COVID-19 vaccine waned after 3 months in children aged 5 to 11 years but was restored by a booster shot, according to study findings published in JAMA Network Open.

Among the study’s authors are Farid Khan, MPH, CMD, lead for global messenger RNA vaccines, analytics and capabilities at Pfizer, and Jennifer L. Nguyen, ScD, MPH, senior director of global clinical epidemiology and COVID-19 vaccines at Pfizer. In written comments credited to both, Khan and Nguyen told Healio that although COVID-19 boosters “continue to remain highly protective” in severe cases of COVID-19, there still exists the potential for people to become infected.

“Boosters are our best protection against current and potential future variants of concern,” they wrote. “We were interested to know the level of protection offered by a booster dose in this age group, especially against the latest omicron subvariants and whether protection was different depending on history of previous infection.”

In a collaboration with Aegis Sciences and the research division of Walgreens, the researchers examined data reported by patients when scheduling a COVID-19 testing appointment at the pharmacy chain.

“We used the test results and the responses from the scheduling questionnaire to measure the effectiveness of the Pfizer‐BioNTech vaccine in preventing SARS‐CoV‐2 infection,” they wrote. “We also controlled for variables such as comorbidities, geography and recent exposure to SARS‐ CoV‐2 because these factors could bias any patterns we observe.”

In a final analysis based on outcomes from around 160,000 children with no evidence of SARS-CoV-2 infection in the previous 90 days, the efficacy of two doses of the vaccine was 85% against the delta variant and 39% against omicron at less than 3 months after adjustments, which decreased to –1% at 3 months or more.

An analysis of children with vs. without prior infection found that protection decreased at around 3 month for both groups, from 58% and 37% at 3 months to 27% and 7% at 3 months or more, respectively.

Vaccine efficacy of a booster dose was 55% against omicron, with no evidence of waning at 3 months or more, the researchers reported.

Khan and Nguyen said the results were “unsurprising” in that they were “consistent with prior studies in older children and adults.”

“We found that booster vaccination improved protection against COVID‐19 among children aged 5 to 11 years,” they wrote. “We were especially curious about the vaccine protection we would observe against omicron BA.4/5 and among children with past SARS‐CoV‐2 infection. We found that the Pfizer‐BioNTech [original] vaccine provided protection across different omicron subvariants, for both children with and without previous infection.”

Omicron booster shots are recommended for kids as young as age 6 months in the U.S.

“Additional studies are also needed describing the duration of protection offered by COVID vaccines, as well as information on more serious outcomes, like hospitalization,” they wrote.