A recent study published in the journal Pediatrics researchers examined the effectiveness of primary vaccination schedules against BNT162b2, messenger ribonucleic acid (mRNA)-1273, and heterologous messenger ribonucleic acid (mRNA) in adolescents against COVID-19-related hospitalizations in Sweden, Norway, Finland, and Denmark.
For adolescent individuals, data on mRNA-1273 and BNT162b2 VE estimates regarding the long-term consequences of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are limited, especially with long-term follow-up. Limited investigations have been conducted on the effectiveness of homologous mRNA-1273 and heterologous messenger RNA vaccinations (i.e., combining mRNA-1273 with BNT162b2).
Study: Effectiveness of COVID-19 Vaccine in Adolescents. Image credit: EDSON DE SOUZA NASCIMENTO / Shutterstock
About the Study
The researchers of the present study examined mRNA-1273, BNT162b2, and heterologous messenger RNA VE in relation to SARS-CoV-2-associated hospitalizations after six months in adolescents. They also provided VE estimates for extended follow-up of one year and the wave of the SARS-CoV-2 Omicron variant.
The researchers conducted national, register-based and 1:1 matched country-specific cohorts in Sweden, Norway, Finland, and Denmark between May 28, 2021, and April 30, 2023, to calculate VE for primary two-dose COVID-19 vaccination schedules in individuals aged 12 to 17 years. They used the inverse variance method to obtain country-specific estimates. Study participants included adolescents without prior COVID-19-related hospitalization, except those who had received COVID-19 vaccinations prior to the analysis or were not residents of the participating countries. During the analysis period, the Delta and Omicron SARS-CoV-2 strains dominated.
The primary study outcome was a SARS-CoV-2-associated hospitalization, including inpatient hospital contacts, a SARS-CoV-2-related diagnosis, and a SARS-CoV-2-positive polymerase chain reaction (PCR) report. Secondary analyses included extending follow-up to a year after vaccination, restricting the analysis to the Omicron wave by stratifying by calendar periods, and examining VE of single-dose vaccinators compared to unvaccinated individuals.
Follow-up began two weeks after the index date until the outcome, six months from the start of follow-up, emigration, death, COVID-19 vaccine booster doses, or the end date of the study, whichever occurred first. The team conducted logistic regressions to calculate propensity scores and estimate the conditional probability of COVID-19 vaccination with specific schedules, taking into account comorbidities, residence, gender, priority groups, and prior COVID-19 history. The team performed random-effects meta-analytic examinations, combining country-specific risk differences (RD) and vaccine efficacy estimates.
The analytical sample included a total of 526,966 two-dose vaccinated individuals and a corresponding number of unvaccinated adolescent individuals. Most of them received BNT162b2 (n=419,168), and mRNA-1273 (homologous) and heterologous messenger RNA vaccinations were more common in Finland compared to other countries. The average participant age in all cohorts ranged from 14 to 17 years. Most vaccinations were administered from July to November 2021. The team observed a low prevalence of comorbidities among participants.
The vaccine efficacy against SARS-CoV-2-related hospital admissions was 73%, with a risk difference of -2.80 for every 10,000 BNT162b2 vaccinees after six months compared to unvaccinated individuals. The corresponding vaccine efficacy and risk difference values were 86.0% and -2.10 for every 10,000 mRNA-1273 vaccinees, and 81.0% and -5.50 for every 10,000 heterologous messenger RNA vaccinees.
In all four Nordic countries, hospitalizations related to COVID-19 were rare among adolescents during follow-up. Among study participants, the number of COVID-19-related hospital admissions increased from less than five to 37 among the vaccinated and from eight to 140 among the unvaccinated during the six months of follow-up. Cumulative COVID-19-associated hospitalization rates were higher among the unvaccinated during follow-up. The COVID-19-related hospitalization rates could not be determined for Norway due to the absence of events among vaccinated adolescents in the study cohorts.
The six-month cross-national vaccine efficacy estimates against laboratory-confirmed SARS-CoV-2 infection were 22%, 3.6%, and 28% for BNT162b2, mRNA-1273, and heterologous COVID-19 vaccinations, respectively. VE for single-dose schedules was low. Extending follow-up to day 365 showed comparable results; cross-national vaccine efficacy estimates against COVID-19 hospital admissions were 66% for BNT162b2, 91% for homologous mRNA-1273 vaccinations, and 83% for heterologous vaccinations. Restricting the analyses to a period of Omicron prevalence did not change the results. A small number of cases influenced efficacy estimates for single-dose vaccination.
Overall, the study results showed that primary mRNA vaccination schedules in Denmark, Finland, Norway, and Sweden provided high protection against hospital admissions in adolescents compared to unvaccinated individuals after six months of follow-up. Homologous mRNA-1273 and heterologous vaccination effectively prevented hospitalizations related to COVID-19, with VE ranging from 73% to 86% after six months. The efficacy of these vaccines remains consistent and extends to one year of follow-up and the SARS-CoV-2 Omicron wave.