Among adolescents, 2 doses of the BNT162b2 COVID-19 vaccine provide strong and sustained protection against infection with the Delta variant but comparatively lower and rapidly wanning protection against the Omicron variant. These findings were published in The Journal of Infectious Diseases.
Researchers at the British Columbia (BC) Centre for Disease Control in Canada performed this test-negative study using data captured from adolescents aged 12 to 17 years living in Quebec and BC. COVID-19 vaccine effectiveness against the Delta and Omicron variants was evaluated among community-dwelling adolescents. The Delta-dominant period was defined as September 5 to November 27, 2021, the Delta-to-Omicron transition period was defined as November 28 to December 18, 2021, and the Omicron-dominant period was defined as December 19 to April 30, 2022. A fully vaccinated status was defined as receipt of the second or third BNT162b2 vaccine dose more than 14 days prior to SARS-CoV-2 testing.
A total of 193,899 tests were performed in Quebec and 60,903 in BC, of which 11% were positive for COVID-19 infection. Of the positive tests, 0.8% and 0.9% represented patients from Quebec and BC, respectively, who required hospitalization. For tests performed in Quebec vs BC, most positive test results (57% vs 78%) were noted during the Omicron period and at 20 or more weeks following receipt of the second vaccine dose (63% vs 68%).
Among patients in both provinces, adjusted 2-dose vaccine effectiveness during the Delta-dominant period exceeded 95%. The effectiveness of the vaccine began to wane during the transition period, to 82.8% in Quebec and 88.0% in BC, with further decreases noted during the Omicron period (41.9% and 33.9%, respectively).
For patients in Quebec, adjusted 2-dose vaccine effectiveness was slightly higher against symptomatic COVID-19 during the Delta (97.3%), transition (87.9%), and Omicron (55.2%) periods compared with those in BC.
Stratified by time since receipt of the second vaccine dose, vaccine effectiveness exceeded 95% from weeks 2 to 3 weeks up to 3 months following vaccination during the Delta period. During the transition period, vaccine effectiveness was less than 80% from weeks 2 to 3 weeks through at least month 5.
There was a rapid decline in vaccine effectiveness observed during the Omicron period following receipt of the second dose, including at 2 to 3 weeks (~65%-75%), 3 to 5 months (~40%-50%), 6 months (33.9%-44.6%), and 7 months (22.2%-33.9%).
The researchers reported an effect of dosing interval on vaccine efficacy during the Omicron period. They found vaccine effectiveness was higher for a dosing interval of 8 or more weeks (35.8%-44.5%) compared with a 3- to 4-week interval (30.0%-37.7%).
For the subset of individuals who received a third vaccine dose, vaccine effectiveness against Omicron was between 63.3% and 65.7% at 14 days or more following vaccination.
This study was limited by the lack of individual patient data, thus no subgroup analyses were performed.
According to the researchers, “[U]pdated vaccine antigens, additional doses and/or extended dosing-intervals may be needed to improve adolescent VE [vaccine effectiveness] against infection due to SARS-CoV-2 immunological-escape variants.”
Ionescu IG, Skowronski DM, Sauvageau C, et al. BNT162b2 effectiveness against Delta and Omicron variants of SARS-CoV-2 in adolescents aged 12-17 years, by dosing interval and duration. J Infect Dis. Published online January 16, 2023. doi:10.1093/infdis/jiad006