Real-world effectiveness of the heterologous SOBERANA-02 and SOBERANA-Plus vaccine scheme in 2–11 years-old children during the SARS-CoV-2 Omicron wave in Cuba: a longitudinal case-population study

Background Increased pediatric COVID-19 occurrence due to the SARS-CoV-2 Omicron variant has raised concerns about the effectiveness of existing vaccines. The protection provided by the SOBERANA-02-Plus vaccination scheme against this variant has not yet been studied. We aimed to evaluate the scheme's effectiveness against symptomatic Omicron infection and severe disease in children. Methods In September 2021, Cuba implemented a mass pediatric immunization with the heterologous SOBERANA-02-Plus scheme: 2 doses of conjugated SOBERANA-02 followed by a heterologous SOBERANA-Plus dose. By December, before the Omicron outbreak, 95.4% of 2–18 years-old had been fully immunized. During the entire Omicron wave, we conducted a nationwide longitudinal post-vaccination case-population study to evaluate the real-world effectiveness of the SOBERANA-02-Plus scheme against symptomatic infection and severe disease in children without previous SARS-CoV-2 infection. The identification of COVID-19 cases relied on surveillance through first line services, which refer clinical suspects to pediatric hospitals where they are diagnosed based on a positive RT-PCR test. We defined the Incidence Rate ratio (IRR) as IRvaccinated age group/IRunvaccinated 1-year-old and calculated vaccine effectiveness as VE = (1—IRR)∗100%. 24 months of age being the ‘eligible for vaccination’ cut-off, we used a regression discontinuity approach to estimate effectiveness by contrasting incidence in all unvaccinated 1-year-old versus vaccinated 2-years-old. Estimates in the vaccinated 3–11 years-old are reported from a descriptive perspective. Findings We included 1,098,817 fully vaccinated 2–11 years-old and 98,342 not vaccinated 1-year-old children. During the 24-week Omicron wave, there were 7003/26,241,176 person-weeks symptomatic COVID-19 infections in the vaccinated group (38.2 per 105 person-weeks in 2-years-old and 25.5 per 105 person-weeks in 3–11 years-old) against 3577/2,312,273 (154.7 per 105 person-weeks) in the unvaccinated group. The observed overall vaccine effectiveness against symptomatic infection was 75.3% (95% CI, 73.5–77.0%) in 2-years-old children, and 83.5% (95% CI, 82.8–84.2%) in 3–11 years-old. It was somewhat lower during Omicron BA.1 then during Omicron BA.2 variant circulation, which took place 1–3 and 4–6 months after the end of the vaccination campaign. The effectiveness against severe symptomatic disease was 100.0% (95% CI not estimated) and 94.6% (95% CI, 82.0–98.6%) in the respective age groups. No child death from COVID-19 was observed. Interpretation Immunization of 2–11 years-old with the SOBERANA-02-Plus scheme provided strong protection against symptomatic and severe disease caused by the Omicron variant, which was sustained during the six months post-vaccination follow-up. Our results contrast with the observations in previous real-world vaccine effectiveness studies in children, which might be explained by the type of immunity a conjugated protein-based vaccine induces and the vaccination strategy used. Funding National Fund for Science and Technology (FONCI-CITMA-Cuba).