Impact and Effectiveness of COVID ‐19 mRNA Vaccination Against COVID ‐19 Hospitalisation in Paediatrics: A Cohort Study Using Two Linked Data Sources in Spain

Purpose Despite Spain's > 2 million COVID‐19 paediatric cases before 2024, few required hospitalisations (8900). We aimed to estimate the effectiveness of two‐dose COVID‐19 vaccinations against hospitalisation ‘with’ and ‘for’ COVID‐19 in paediatrics. Methods All individuals aged 5–14 years between January 2021 and February 2022 in two databases in Spain (SIDIAP and BIFAP) vaccinated against COVID‐19 (two doses) were matched 1:1 to unvaccinated controls with the same age, sex, region and comorbidities on the dates of vaccination. Individuals with previous SARS‐CoV‐2 infections were excluded. COVID‐19 was identified as the main reason (hospitalisation ‘for’ COVID‐19; SIDIAP) or as one of the reasons (hospitalisation ‘with’ COVID‐19; BIFAP) for hospitalisation with a positive SARS‐CoV‐2 test ±30 days. Incidence rate differences and vaccine effectiveness (VE; 95% CI; controlled by inverse probability weights) against hospitalisations ‘for’ and ‘with’ COVID‐19 were calculated. Results The cohorts included 75 361 (SIDIAP) and 178 589 (BIFAP) pairs. Among vaccinated individuals (99.99% with mRNA vaccines) and controls, < 5 and 15 hospitalisations ‘for’ COVID‐19 were identified (SIDIAP), whereas 21 and 32 hospitalisations ‘with’ COVID‐19 (BIFAP), all aged 12–14 years old. Vaccination prevented 2.5 hospitalisations ‘for’ and 0.5 ‘with’ COVID‐19 during the Delta period, and 0.8 hospitalisations ‘with’ COVID‐19 during Omicron predominance per 10 6 person‐days. The VE was 94% (95% CI: 52%–99%; SIDIAP) and 53% (95% CI: 18%–74%; BIFAP). Conclusions Given the low incidence of hospitalised COVID‐19, two‐dose series mRNA vaccination showed moderate‐high effectiveness with few averted cases. Including hospitalisation ‘with’ COVID‐19 underestimated the effectiveness. If paediatric severe COVID‐19 remains rare, larger databases are required to understand precisely the effectiveness and impact of new vaccines. Trial Registration: EU PAS Register number: EUPAS47725