Pfizer’s Covid-19 vaccine was highly effective against the Delta variant in adolescents in Israel, where Covid-19 vaccination for the adolescent population started earlier than in Korea.
A research team at Boston Children’s Hospital said it used data from Clalit Health Services, the largest health care organization in Israel, to conduct a study involving adolescents between the ages of 12 and 18 who had no prior Covid-19 infection.
The team published the study results in the New England Journal of Medicine (NEJM) on Wednesday.
The adolescents who participated in the study received Pfizer’s Covid-19 vaccine between June 8 and Sept. 14. At the time, over 95 percent of Covid-19 cases in Israel occurred due to the transmission of the Delta variant.
Of the 184,905 vaccinated adolescents, the research team matched 94,352 vaccinated people to 94,354 unvaccinated controls. The researchers observed them 27 days after the first dose.
The results showed that Covid-19 infection curves showed similar patterns in the early stage in both the vaccinated and the unvaccinated groups. However, the incidence of Covid-19 rose more slowly in the vaccinated group, the research team said.
Pfizer vaccine’s effectiveness in adolescents was 59 percent on days 14 through 20 after the first dose and 66 percent on days 21 to 27 after the first dose. The preventive effect rose to 90 percent on days seven to 21 after the second dose.
The estimated vaccine effectiveness against symptomatic Covid-19 was 82 percent on days 21 to 27 after the first dose and 93 percent on days 7 to 21 after the second dose.
The research team cited a randomized trial, saying two doses of Pfizer vaccine were 100 percent effective against non-Delta variants in adolescents aged between 12 and 15 who have no history of Covid-19 infection.
“The present observational study provides substantially more precise estimates of vaccine effectiveness among adolescents between the ages of 12 and 18 years for both documented infection and symptomatic disease in a setting in which the Delta variant was predominant,” the research team said.
The researchers concluded that the Pfizer vaccine was highly effective in the first few weeks after vaccination against not only Covid-19 but the Delta variant among adolescents aged 12 to 18.
In Korea, the vaccination for people aged 12 to 17 (born between 2004 and 2009) began on Monday. The government said 55.5 percent out of 899,000 adolescents aged 16 and 17 have completed the reservation for Covid-19 jabs at Sunday midnight.
Adolescents aged 16 and 17 can book for vaccination until 6 p.m. on Oct. 29. Those aged between 12 and 15 can make reservations until 6 p.m. on Nov. 12.