By April 13, 2022, more than 4 months after the approval of BNT162b2 (Pfizer–BioNTech) for children, less than 40% of 5–11-year-olds in Italy had been vaccinated against COVID-19. Estimating how effective vaccination is in 5–11-year-olds in the current epidemiological context dominated by the omicron variant (B.1.1.529) is important to inform public health bodies in defining vaccination policies and strategies.
In this retrospective population analysis, we assessed vaccine effectiveness against SARS-CoV-2 infection and severe COVID-19, defined as an infection leading to hospitalisation or death, by linking the national COVID-19 surveillance system and the national vaccination registry. All Italian children aged 5–11 years without a previous diagnosis of infection were eligible for inclusion and were followed up from Jan 17 to April 13, 2022. All children with inconsistent vaccination data, diagnosed with SARS-CoV-2 infection before the start date of the study or without information on the municipality of residence were excluded from the analysis. With unvaccinated children as the reference group, we estimated vaccine effectiveness in those who were partly vaccinated (one dose) and those who were fully vaccinated (two doses).
By April 13, 2022, 1 063 035 (35·8%) of the 2 965 918 children aged 5–11 years included in the study had received two doses of the vaccine, 134 386 (4·5%) children had received one dose only, and 1 768 497 (59·6%) were unvaccinated. During the study period, 766 756 cases of SARS-CoV-2 infection and 644 cases of severe COVID-19 (627 hospitalisations, 15 admissions to intensive care units, and two deaths) were notified. Overall, vaccine effectiveness in the fully vaccinated group was 29·4% (95% CI 28·5–30·2) against SARS-CoV-2 infection and 41·1% (22·2–55·4) against severe COVID-19, whereas vaccine effectiveness in the partly vaccinated group was 27·4% (26·4–28·4) against SARS-CoV-2 infection and 38·1% (20·9–51·5) against severe COVID-19. Vaccine effectiveness against infection peaked at 38·7% (37·7–39·7) at 0–14 days after full vaccination and decreased to 21·2% (19·7–22·7) at 43–84 days after full vaccination.
Vaccination against COVID-19 in children aged 5–11 years in Italy showed a lower effectiveness in preventing SARS-CoV-2 infection and severe COVID-19 than in individuals aged 12 years and older. Effectiveness against infection appears to decrease after completion of the current primary vaccination cycle.