In a recent study published in the journal Pediatricsinvestigators evaluated the effectiveness of primary BNT162b2, messenger ribonucleic acid (mRNA)-1273, and heterologous messenger ribonucleic acid (mRNA) vaccination programs among adolescents against hospitalization-associated coronavirus disease 2019 (COVID-19) in Sweden, Finland, Norway, Denmark.
For adolescents, data on estimates of mRNA-1273 and BNT162b2 VE versus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection outcomes in the long term are limited, especially with long-term follow-up. Limited research has been conducted on the efficacy of mRNA-1273 homologous and heterologous messenger RNA vaccinations (ie, combination of mRNA-1273 with BNT162b2).
Study: Effectiveness of the COVID-19 vaccine among adolescents. Image credit: EDSON DE SOUZA NASCIMENTO / Shutterstock
About the study
The present study investigators evaluated mRNA-1273, BNT162b2, and heterologous messenger RNA VE against SARS-CoV-2-related hospitalization at six months in adolescents. They also provided VE estimates for extended one-year follow-ups and the Omicron SARS-CoV-2 variant wave.
Researchers conducted national registries and matched 1:1 country cohorts in Sweden, Norway, Finland and Denmark between 28 May 2021 and 30 April 2023 to estimate the VE for the main two-dose vaccination schedules for COVID-19 between persons aged between 12 and 17 years. They used the inverse variance method to obtain country-specific estimates. Study participants included adolescents without prior hospitalization related to COVID-19, excluding those who received vaccinations for COVID-19 before the analysis or were non-residents of the participating countries. SARS-CoV-2 Delta and Omicron strains predominated during the analysis period.
The primary study outcome was SARS-CoV-2-related hospitalization, including hospital-acquired contacts, SARS-CoV-2-related diagnosis, and a positive SARS-CoV-2 polymerase chain reaction (PCR) report. Secondary analyzes included extensions of follow-up to one year post-vaccination, restriction of analysis to the Omicron wave with stratification by calendar period, and examination of single-dose VE vaccinated compared with unvaccinated subjects.
Follow-up began two weeks after the index date until outcome, six months after start of follow-up, emigration, death, booster doses of COVID-19 vaccines, or study end date, whichever occurred first . The team performed logistic regression to calculate propensity scores and estimate the conditional probability of timing-specific vaccination against COVID-19 based on comorbidities, place of residence, sex, priority groups, and prior history of COVID-19. The team performed a random-effects meta-analysis, combining country risk differences (RD) and estimates of vaccine effectiveness.
Results
Overall, the analytic sample included 526,966 two-dose vaccinees and an equivalent number of unvaccinated adolescents. Most of them received BNT162b2 (n=419,168) and in Finland, mRNA-1273 (homologous) and heterologous messenger RNA vaccinations were more frequent compared to other countries. The mean age of participants ranged between 14 and 17 years across all cohorts. Most vaccinations took place between July and November 2021. The team observed a low prevalence of comorbidities among participants.
Vaccine efficacy against SARS-CoV-2-associated hospitalization was 73%, with a risk difference of -2.80 among every 10,000 BNT162b2 vaccinated at six months compared with unvaccinated individuals. The corresponding vaccine efficacy and risk difference values were 86.0% and -2.10 among every 10,000 vaccinated mRNA-1273 and 81.0% and -5.50 among every 10,000 heterologous messenger RNA vaccinated.
In all four Nordic nations, hospitalization related to COVID-19 was rare among adolescents during follow-up. Among the study subjects, the number of hospitalizations related to COVID-19 during the six-month follow-up period dropped from less than five to 37 and eight to 140 among the vaccinated and unvaccinated, respectively. At follow-up, cumulative rates of hospitalizations related to COVID-19 were higher among the unvaccinated. Hospitalization rates related to COVID-19 could not be determined for Norway due to a lack of events among vaccinated adolescents in the study cohorts.
Estimates of six-month efficacy of the combination vaccine in a country against laboratory-confirmed SARS-CoV-2 infection were 22%, 3.6%, and 28% for the BNT162b2, mRNA-1273, and heterologous COVID-19 vaccines, respectively. VE for single-dose regimens was low. Extending follow-up to day 365 showed comparable results. Country combination vaccine efficacy estimates against hospitalizations for COVID-19 were 66% for BNT162b2, 91% for homologous mRNA-1273 vaccines, and 83% for heterologous vaccinations. Restricting the analyzes to prevalence period o did not change the findings. A small number of cases affected the efficacy estimates for single-dose vaccination.
Overall, the study findings showed that mRNA primary vaccination programs provide high protection against adolescent hospitalizations compared to unvaccinated individuals at six months of follow-up in Denmark, Finland, Norway and Sweden. The mRNA-1273 homologue and heterologous vaccinations effectively prevented hospitalization associated with COVID-19, with VE ranging between 73% and 86% at six months. The efficacy of these vaccines remains stable, extending follow-up to one year and the Omicron SARS-CoV-2 wave.
