— Israeli case-control study finds vaccine effective 2 to 4 weeks following second dose
by Molly Walker, Deputy Managing Editor,
MedPage
September 28, 2021
The Pfizer-BioNTech COVID-19 vaccine (Comirnaty) was effective against the Delta variant among adolescents ages 12 to 15 in the month following vaccination, a real-world case-control study from Israel found.
Following the administration of the second dose of vaccine during the month of July, adjusted vaccine effectiveness against laboratory-confirmed SARS-CoV-2 at 2 to 4 weeks later was 91.5% (95% CI 88.2-93.9%), reported Aharona Glatman-Freedman, MD, of the Israel Center for Disease Control in Ramat Gan, and colleagues.
As of August 26, no vaccinated adolescents who tested positive up to 28 days after their second vaccine dose were hospitalized, the authors wrote in Emerging Infectious Diseases.
A two-dose regimen of Pfizer vaccine was authorized for adolescents ages 12 to 15 by the FDA in May. The New England Journal of Medicine published more detailed data on the phase III trial that supported the emergency use authorization (EUA), which showed high vaccine efficacy and a similar safety profile to adults receiving the vaccine.
However, as these data were collected during the phase III trial, from October 2020 to January 2021, there were no data on vaccine efficacy against the Delta variant in this age group.
Glatman-Freedman and colleagues noted that Israel started vaccinating adolescents ages 12 to 15 beginning on June 2 of this year, and by August 26, 31% of eligible adolescents had been fully vaccinated with two doses of vaccine, administered 21 days apart. They also noted that in mid-June, Israel had an outbreak of the Delta variant, which comprised nearly all sequenced virus samples in the country in July and August.
The team examined data from adolescents who received the second dose of vaccine from July 1 to 24. To derive vaccine effectiveness, they looked at the number of positive tests for SARS-CoV-2 via RT-PCR. They used unvaccinated adolescents as controls, which they calculated by subtracting the number of fully vaccinated adolescents from those without a positive SARS-CoV-2 test, who had not received a first dose of vaccine.
During weeks 2 to 4 following the second dose, there were 8,144 positive tests for SARS-CoV-2 in the unvaccinated cohort compared with 124 in the vaccinated cohort. Crude vaccine effectiveness began at 55.3% (95% CI 41.3-66.0%) a week after the second dose, but the numbers quickly rose in the following weeks:
- 87.1% (95% CI 81.0-91.2%) after 2 weeks
- 91.2% (95% CI 87.4-93.8%) after 3 weeks
- 88.2% (95% CI 85.0-90.7%) after 4 weeks
Glatman-Freedman and colleagues explained they could not estimate vaccine effectiveness against symptomatic disease because epidemiological investigation was only performed for a minority of the vaccinated and unvaccinated cohorts (42% and 40%, respectively).
While none of vaccinated adolescents who tested positive on days 1 to 28 following the second dose were hospitalized, seven unvaccinated adolescents were hospitalized at 1 to 7 days after the vaccinated cohort’s second dose, and 26 of the unvaccinated adolescents were hospitalized at 8 to 28 days. There were no deaths in either cohort among those testing positive, the authors noted.
They also said that because the number of cases among vaccinated adolescents was so low on a weekly basis, they could not adjust for weekly vaccine effectiveness.
“Our results demonstrate high vaccine effectiveness against SARS-CoV-2 infection in this population starting the second week after the second vaccine dose,” they wrote. “[Pfizer] vaccine provides adolescents with highly effective short-term protection against the SARS-CoV-2 Delta variant.”
Source: https://www.medpagetoday.com/infectiousdisease/covid19vaccine/94740?trw=no