Vaccine effectiveness with BNT162b2 (Comirnaty, Pfizer-BioNTech) vaccine against reported SARS-CoV-2 Delta and Omicron infection among adolescents, Norway, August 2021 to January 2022

  1. Lamprini Veneti
  2. Jacob Dag Berild
  3. Sara Viksmoen Watle
  4. Jostein Starrfelt
  5. Margrethe Greve-Isdahl
  6. Petter Langlete
  7. Håkon Bøås
  8. Karoline Bragstad
  9. Olav Hungnes
  10. Hinta Meijerink

Reviewed by

Read the full article See related articles

Listed in

Log in to save this article

Abstract

Background

COVID-19 vaccination was recommended for adolescents in Norway since August 2021. In this population-based cohort study, we estimated the BNT162b2 vaccine effectiveness against any PCR-confirmed (symptomatic or not) SARS-CoV-2 infections caused by the Delta and Omicron variant among adolescents (12-17-years-old) in Norway from August 2021 to January 2022.

Methods

Using Cox proportional hazard models, we estimated the BNT162b2 vaccine effectiveness against any Delta and Omicron infections. Vaccine status was included as a time-varying covariate and models were adjusted for age, sex, comorbidities, county of residence, country of birth, and living conditions. Data were obtained from the National Preparedness registry for COVID-19, which contains individual-level data from national health and administrative registries.

Findings

Vaccine effectiveness against Delta infection peaked at 68% (95%CI: 64–71%) and 62% (95%CI: 57– 66%) in days 21-48 after the first dose among 12–15-year-olds and 16–17-year-olds respectively. Among 16–17-year-olds that received two doses, vaccine effectiveness peaked at 93% (95%CI: 90–95%) in days 35-62 and declined to 84% (95%CI: 76–89%) in 63 days or more after the second dose. For both age-groups, we found no protection against Omicron infection after receiving one dose. Among 16–17-year-olds, vaccine effectiveness against Omicron infection peaked at 53% (95%CI: 43–62%) in 7-34 days after the second dose and decreased to 23% (95%CI: 3–40%) in 63 days or more after vaccination. Vaccine effectiveness decreased with time since vaccination for both variants, but waning was observed to occur faster for Omicron.

Interpretation

Our results suggest reduced protection from BNT162b2 vaccination against any SARS-CoV-2 infection caused by the Omicron variant compared to the Delta. In addition, waning immunity was observed to occur faster for Omicron. The impact of vaccination among adolescents on reducing infection and thus transmission is limited during omicron dominance.

Funding

No funding was received.

Research in context

Evidence before this study

BNT162b2 (Comirnaty, Pfizer-BioNTech) and mRNA-1273 (Spikevax, Moderna) vaccines have been approved for use in adolescents, based on results from randomized placebo-controlled trials demonstrating comparable immunogenicity and safety profile as in young adults. In addition, observational studies from Israel, the USA and England have reported high protection of BNT162b2 vaccines against SARS-CoV-2 Delta infection among adolescents. These studies also reported decrease in effectiveness with time since last vaccine dose. Evidence on the effect of an extended interval between doses, longer time since vaccination and the effect against different variants is limited. When we first planned this study in early February 2022, no data were available regarding vaccine effectiveness against SARS-CoV-2 Omicron infection among adolescents. To our knowledge when we completed this study and before submitting this article, only one study from England reported results in a preprint on vaccine effectiveness against symptomatic SARS-CoV-2 Omicron infection among adolescents. We searched for studies that evaluated vaccine efficacy or effectiveness after vaccination of adolescents during 2021-2022 in PubMed, medRxiv, bioRxiv, SSRN. We searched for studies with several variations of the primary key search terms “COVID-19”, “SARS-CoV-2”, and “vaccine” (including names of specific vaccines, as BNT162b2), “vaccine effectiveness”, “adolescents”, “children”.

Added value of this study

The rapid increase in the incidence of SARS-CoV-2 infection caused by the Omicron variant in highly vaccinated populations has raised concerns about the effectiveness of current vaccines in adults but also adolescents. In this population-based cohort study, we showed that the vaccine effectiveness against Omicron is lower than against Delta infections among adolescents, including symptomatic and asymptomatic infections. We should note that evidence suggests higher rates of asymptomatic carriage for Omicron than other variants of concern. Vaccine effectiveness that includes asymptomatic cases, as in the study from England, is expected to be lower than when including symptomatic cases only. We found that one and two doses of BNT162b2 among adolescents protected well against Delta. Vaccination provided high protection against Delta infections (>91%) among Norwegian 16-17-year-olds 7-62 days after the second dose. We found no protection against Omicron SARS-CoV-2 infection after one vaccine dose, and moderate effectiveness after two doses (peaked at 53%) among the 16-17-year-olds. Moreover, waning immunity was observed to occur faster for Omicron.

Implications of all the available evidence

Based on the available evidence, the vaccine effectiveness among adolescents is similar to that reported among adults, also with an extended period of 8-12 weeks between doses which was used in Norway. Protection is significantly lower against Omicron than Delta infections and immunity wanes faster against Omicron. The impact of vaccination among adolescents on reducing infection and thus transmission is limited during omicron dominance. Policies should take into account the impact of vaccination campaigns among adolescents and their primary objective. Vaccine effectiveness should be re-evaluated when other variants appear as they might have different outcomes as shown between Delta and Omicron infections.

Article activity feed

  1. ScreenIT

    SciScore for 10.1101/2022.03.24.22272854: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsIRB: Ethics approval: Ethical approval was granted by Regional Committees for Medical and Health Research Ethics (REC) Southeast (reference number 122745).
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    The study also has some limitations. For the combined registries there can be errors for specific individuals, missing individuals, and older data (e.g county of residence, household crowding). Data used from these registries are not collected for the purpose of this study alone and some details might not be as precise. But there is no reason to believe that such discrepancies, if they exist, would differ among the different groups that we have compared. Various aspects related to disease dynamics, risk of infection, testing strategy, and response changed over the study period, making it challenging to identify all elements that affect vaccine effectiveness and risk of infection. However, we expect these changes to be similar between the adolescents in this study and by using time explicitly in our models we take some of these changes indirectly into consideration. However, residual confounding may still be present. The sensitivity analyses using data from only cases screened for variants compared to all reported cases provided similar estimates on vaccine effectiveness (supplementary material, part 2). Therefore, we conclude that using all reported SARS-CoV-2 cases in periods with one variant dominating can provide similar vaccine effectiveness estimates with larger power when only a small proportion of samples are screened. Even though testing capacity is high in Norway and regular testing was recommended for adolescents in areas and periods with high infection rates that a...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  2. Version published to 10.1101/2022.03.24.22272854v1 on medRxiv