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Pfizer vaccination ‘highly effective’ against Delta in adolescents — Israel study

The Pfizer-BioNTech COVID-19 vaccine (Comirnaty) was effective against the Delta variant among adolescents aged 12 to 15 in the month after vaccination, a case-control study from Israel found.

After the second dose of vaccine in July, adjusted vaccine effectiveness against laboratory- confirmed SARS-CoV-2 at two to four weeks later was 91.5%, according to Dr Aharona Glatman-Freedman of the Israel Center for Disease Control in Ramat Gan, and colleagues.

As of 26 August, no vaccinated adolescents who tested positive up to 28 days after their second vaccine dose were hospitalised, the authors wrote in Emerging Infectious Diseases.

A two-dose regimen of Pfizer vaccine was authorised for 12- to 15-year-olds by the US Food & Drug Administration in May. The New England Journal of Medicine published more detailed data on the phase III trial that supported the emergency use authorisation (EUA), which showed high vaccine efficacy and a similar safety profile to adults receiving the vaccine, writes MedPage Today.

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 said Israel started vaccinating adolescents aged 12 to 15 from 2 June of this year, and by 26 August , 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 1-24 July. 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.

Crude vaccine effectiveness began at 55.3% a week after the second dose, but the numbers quickly rose in the following weeks: 87.1%  after two weeks 91.2% after three weeks 88.2% after four weeks

Glatman-Freedman and colleagues said 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 after the second dose was hospitalised, seven unvaccinated adolescents were hospitalised at one to seven days after the vaccinated cohort's second dose, and 26 of the unvaccinated adolescents were hospitalised at eight 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.”


Study details
Effectiveness of BNT162b2 Vaccine in Adolescents during Outbreak of SARS-CoV-2 Delta Variant Infection, Israel, 2021

Aharona Glatman-Freedman, Yael Hershkovitz, Zalman Kaufman, Rita Dichtiar, Lital Keinan-Boker, and Michal Bromberg

Published in Emerging Infectious Diseases Volume 27, No 11, November 2021


In Israel, the BNT162b2 vaccine against severe acute respiratory syndrome coronavirus 2 was approved for use in adolescents in June 2021, shortly before an outbreak of B.1.617.2 (Delta) variant–dominant infection. We evaluated short-term vaccine effectiveness and found the vaccine to be highly effective among this population in this setting.

Vaccine doses among adolescents and total severe acute respiratory syndrome coronavirus 2 infections, Israel, June 1–August 26, 2021. A) Daily frequency of administration of first and second dose of BNT162b2…
In May 2021, the US Food and Drug Administration and the European Medicines Agency expanded existing authorization for BNT162b2 vaccine (Pfizer-BioNTech) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to include its use in adolescents 12–15 years of age. On June 2, 2021, the Israel Ministry of Health declared the availability of BNT162b2 vaccine for adolescents 12–15 years of age as a 2-dose regimen, given 21 days apart.

By August 26, 2021, a total of 277,218 adolescents (46.1% of those eligible) had received 1 dose of the vaccine and 187,707 (31.2%) had received 2 doses. In mid-June 2021, after a month of extremely low SARS-CoV-2 activity in Israel, 2 local outbreaks erupted. These outbreaks marked the beginning of a new widespread SARS-CoV-2 outbreak in Israel dominated by the B.1.617.2 (Delta) variant, which accounted for 93%–99% of the sequenced viruses during July and August 2021.

We analysed effectiveness of this vaccine among adolescents who had been vaccinated in the early stages of this outbreak in Israel. The study was approved by the superior ethical committee of the Israel Ministry of Health and included exemption from informed consent.

Our findings are consistent with those of a recent study from the United Kingdom, which demonstrated vaccine effectiveness of 88.0% (95% CI 85.3%–90.1%) against symptomatic disease caused by the SARS-CoV-2 Delta variant, compared with vaccine effectiveness of 93.7% (95% CI 91.6%–95.3%) against disease caused by the Alpha variant among persons >16 years of age who had received two doses of BNT162b2 (11). However, that study addressed neither the interval between the two doses nor the exact interval between assessment of vaccine effectiveness and the date of the second dose.

As of September 2021, two controlled studies had assessed vaccine efficacy in adolescents, without specifying the SARS-CoV-2 variant. One study reported BNT162b2 vaccine efficacy of 100% against laboratory-confirmed COVID-19 >7 days after receipt of the second vaccine dose at 21 days after the first dose. The other study reported that vaccine efficacy of the mRNA-1273 vaccine 14 days after the second dose was difficult to assess because of the low incidence of laboratory-confirmed COVID-19 in the trial population (4 cases in the placebo group and 0 cases in the mRNA-1273 group. Of note, the geometric mean ratio of neutralising antibodies in adolescents receiving those vaccines was similar to or greater than that of young adults after receipt of two doses.

Behavioural and testing policy factors can potentially affect estimations of vaccine effectiveness. BehavioUrs that increase exposure to SARS-CoV-2 may be assumed by vaccinated or unvaccinated adolescents for different reasons and are difficult to measure. During the study period, SARS-CoV-2 testing was available in Israel regardless of vaccination status. The recent rise in SARS-CoV-2 cases in Israel raised two concerns. The first concern was that BNT162b2 vaccine–elicited immunity was waning. Waning of spike protein antibody levels was detected over time after receipt of a second dose of SARS-CoV-2 vaccines. The second concern was that the vaccine was not effective against the SARS-CoV-2 Delta variant. However, our findings indicate that the BNT162b2 vaccine provides adolescents with highly effective short-term protection against the SARS-CoV-2 Delta variant.


Study details

Safety, Immunogenicity, and Efficacy of the BNT162b2 Covid-19 Vaccine in Adolescents

Robert W. Frenck, Jr., Nicola P. Klein, Nicholas Kitchin, Alejandra Gurtman, Judith Absalon, Stephen Lockhart, John L. Perez, Emmanuel B. Walter, Shelly Senders, Ruth Bailey, Kena A. Swanson, Hua Ma, et al., for the C4591001 Clinical Trial Group

Published in New England Journal of Medicine on 15 July 2021


Until very recently, vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had not been authorised for emergency use in persons younger than 16. Safe, effective vaccines are needed to protect this population, facilitate in-person learning and socialisation, and contribute to herd immunity.

In this ongoing multinational, placebo-controlled, observer-blinded trial, we randomly assigned participants in a 1:1 ratio to receive two injections, 21 days apart, of 30 μg of BNT162b2 or placebo. Noninferiority of the immune response to BNT162b2 in 12-to-15-year-old participants as compared with that in 16-to-25-year-old participants was an immunogenicity objective. Safety (reactogenicity and adverse events) and efficacy against confirmed coronavirus disease 2019 (COVID-19; onset, ≥7 days after dose 2) in the 12-to-15-year-old cohort were assessed.

Overall, 2,260 adolescents 12 to 15 years of age received injections; 1,131 received BNT162b2, and 1,129 received placebo. As has been found in other age groups, BNT162b2 had a favourable safety and side-effect profile, with mainly transient mild-to-moderate reactogenicity (predominantly injection-site pain [in 79 to 86% of participants], fatigue [in 60 to 66%], and headache [in 55 to 65%]); there were no vaccine-related serious adverse events and few overall severe adverse events. The geometric mean ratio of SARS-CoV-2 50% neutralising titers after dose 2 in 12-to-15-year-old participants relative to 16-to-25-year-old participants was 1.76 (95% confidence interval [CI], 1.47 to 2.10), which met the noninferiority criterion of a lower boundary of the two-sided 95% confidence interval greater than 0.67 and indicated a greater response in the 12-to-15-year-old cohort. Among participants without evidence of previous SARS-CoV-2 infection, no COVID-19 cases with an onset of 7 or more days after dose 2 were noted among BNT162b2 recipients, and 16 cases occurred among placebo recipients. The observed vaccine efficacy was 100% (95% CI, 75.3 to 100).

The BNT162b2 vaccine in 12-to-15-year-old recipients had a favourable safety profile, produced a greater immune response than in young adults, and was highly effective against COVID-19.


Emerging Infectious Diseases study: Effectiveness of BNT162b2 Vaccine in Adolescents during Outbreak of SARS-CoV-2 Delta Variant Infection, Israel, 2021 (Open access)


NEJM study: Safety, Immunogenicity, and Efficacy of the BNT162b2 Covid-19 Vaccine in Adolescents (Open access)


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CDC investigates 'relatively few' reports of myocarditis from Pfizer vaccination


Healthy boys at greater risk from vaccination than COVID itself — US analysis


FDA authorises Pfizer vaccine for adolescents



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