A new study points to the Pfizer shot's initially limited protection against the COVID-19 Omicron variant in those aged 5-11 years and also the the value of vaccine boosters.
Protection against the Omicron variant from a 2-dose series of the Pfizer-BioNTech COVID-19 monovalent vaccine (BNT162b2) waned after 3 months in children aged 5-11 years but was restored by a monovalent booster shot, according to new research published in JAMA Network Open.
Findings showed that among children with no evidence of prior SARS-CoV-2 infection, the efficacy of 2 doses of BNT162b2 against the Omicron variant at less than 3 months was 39% and at 3 months or more was reduced to -1%.
“The available evidence describing vaccine effectiveness (VE) among children aged 5 to 11 years suggests that 2 doses of BNT162b2 provided modest protection (approximately 30%-60% VE) against Omicron-related infection, symptomatic COVID-19, and COVID-19-related urgent or emergency care visits through approximately 2 to 3 months after receipt of the second dose,” wrote researchers led by Farid L. Khan, MPH, medical development & scientific clinical affairs, Pfizer.
“The VE of a booster dose has not yet been reported for this age group, to our knowledge. In addition, previously published VE estimates have not been stratified by history of prior infection—which is becoming increasingly important for understanding vaccine performance given high levels of seroprevalence among this age group at this point in the pandemic,” continued Khan and colleagues.
To estimate the effectiveness of BNT162b2 against SARS-CoV-2 infection among children aged 5-11 years during Delta (November 2 to December 9, 2021)and Omicron (January 16 to September 30, 2022) variant-predominant periods, the team collaborated with Aegis Sciences and the research division of Walgreens to examine data reported by patients when scheduling a COVID-19 testing appointment at the pharmacy chain.
Investigators used test results and the responses from a scheduling questionnaire to measure VE of BNT162b2. The primary outcome was SARS-CoV-2 infection confirmed by polymerase chain reaction (PCR) and the secondary outcome was confirmed symptomatic infection. Adjusted estimated VE was calculated from multilevel logistic regression models, according to the study.
In the final analysis based on outcomes from 160 002 children with no evidence of SARS-CoV-2 infection in the previous 90 days, the adjusted VE of 2 doses of BNT162b2 was 85% against the Delta variant and 39% against Omicron at less than 3 months, which decreased to –1% at ≥3 months.
An analysis comparing participants with prior SARS-CoV-2 infection to those without showed that protection decreased at approximately 3 months for both groups, from 58% and 37% at 3 months to 27% and 7% at ≥3 months, respectively. The VE of a booster dose was 55% against Omicron, with no evidence of waning at ≥3 months, according to the results.
“These findings highlight the continued benefits associated with booster doses in maintaining protection against SARS-CoV-2 in individuals with or without a history of COVID-19. Future VE studies are needed to describe the level of protection and longer-term durability provided by monovalent and bivalent COVID-19 vaccines against more severe end points among this age group,” concluded Khan et al.
Reference: Khan FL, Nguyen JL, Singh TG, et al. Estimated BNT162B2 vaccine effectiveness with delta and omicron variants among US children 5 to 11 years of age. JAMA Netw Open. 2022;5(12):e2246915. doi: 10.1001/jamanetworkopen.2022.46915