Effectiveness of BBIBP-CorV, BNT162b2 and mRNA- 1273 vaccines against hospitalisations among children and adolescents during the Omicron outbreak in Argentina: a retrospective cohort study

Background Although paediatric clinical presentations of COVID-19 are usually less severe than in adults, serious illness and death have occurred. Many countries started the vaccination rollout of children in 2021; still, information about effectiveness in the real-world setting is scarce. The aim of our study was to evaluate vaccine effectiveness (VE) against COVID-19-associated-hospitalisations in the 3−17-year population during the Omicron outbreak. Methods We conducted a retrospective cohort study including individuals aged 3−17 registered in the online vaccination system of the Buenos Aires Province, Argentina. mRNA-1273 and BNT162b2 were administered to 12−17- year subjects; and BBIBP-CorV to 3−11-year subjects. Vaccinated group had received a two-dose scheme by 12/1/ 2021. Unvaccinated group did not receive any COVID-19 vaccine between 12/14/2021 and 3/9/2022, which was the entire monitoring period. Vaccine effectiveness (VE) against COVID-19-associated hospitalisations was calculated as (1-OR)x100. Findings By 12/1/2021, 1,536,435 individuals aged 3−17 who had received zero or two doses of SARS-CoV-2 vaccines were included in this study. Of the latter, 1,440,389 were vaccinated and 96,046 not vaccinated. VE were 78.0% [68.7−84.2], 76.4%[62.9−84.5] and 80.0%[64.3−88.0] for the entire cohort, 3−11-year (BBIBP-CorV) subgroup and 12−17 (mRNA vaccines) subgroup, respectively. VE for the entire population was 82.7% during the period of Delta and Omicron overlapping circulation and decreased to 67.7% when Omicron was the only variant present. Interpretation This report provides evidence of high vaccine protection against associated hospitalisations in the paediatric population during the Omicron outbreak but suggests a decrease of protection when Omicron became predominant. Application of a booster dose in children aged 3−11-year warrants further consideration

Protection of homologous and heterologous boosters after primary schemes of rAd26-rAd5, ChAdOx1 nCoV-19 and BBIBP-CorV during the omicron outbreak in adults of 50 years and older in Argentina: a test-negative case–control studyResearch in context

Summary: Background: After primary vaccination schemes with rAd26-rAd5 (Sputnik V), ChAdOx1 nCoV-19, BBIBP-CorV or heterologous combinations, the effectiveness of homologous or heterologous boosters (Sputnik V, ChAdOx, Pfizer-BioNTech, Moderna) against SARS-CoV-2 infections, hospitalisations and deaths has been scarcely studied. Methods: Test-negative, case–control study, conducted in Argentina during omicron BA.1 predominance, in adults ≥50 years old tested for SARS-CoV-2 who had received two or three doses of COVID-19 vaccines. Outcomes were COVID-associated infections, hospitalisations and deaths after administering mRNA and vectored boosters, < or ≥60 days from the last dose. Findings: Of 422,124 individuals tested for SARS-CoV-2, 221,993 (52.5%) tested positive; 190,884 (45.2%) and 231,260 (54.8%) had received 2-dose and 3-dose vaccination schemes, respectively. The 3-dose scheme reduced infections, hospitalisations and death (OR 0.81 [0.80–0.83]; 0.28 [0.25–0.32] and 0.25 [0.22–0.28] respectively), but protection dropped after 60 days to 1.04 [1.01–1.06]; 0.52 [0.44–0.61] and 0.38 [0.33–0.45]). Compared with 2-dose-schemes, homologous boosters after primary schemes with vectored-vaccines provided lower protection against infections < and ≥60 days (0.94 [0.92–0.97] and 1.05 [1.01–1.09], respectively) but protected against hospitalisations (0.30 [0.26–0.35]) and deaths (0.29 [0.25–0.33]), decreasing after 60 days (0.59 [0.47–0.74] and 0.51 [0.41–0.64], respectively). Heterologous boosters protected against infections (0.70 [0.68–0.71]) but decreased after 60 days (1.01 [0.98–1.04]) and against hospitalisations and deaths (0.26 [0.22–0.31] and 0.22 [0.18–0.25], respectively), which also decreased after 60 days (0.43 [0.35–0.53] and 0.33 [0.26–0.41], respectively). Heterologous boosters protected against infections when applied <60 days (0.70 [0.68–0.71], p < 0.001), against hospitalisations when applied ≥60 days (0.43 [0.35–0.53], p < 0.01), and against deaths < and ≥60 days (0.22 [0.18–0.25], p < 0.01 and 0.33 [0.26–0.41], p < 0.001). Interpretation: During omicron predominance, heterologous boosters such as viral vectored and mRNA vaccines, following Sputnik V, ChAdOx1, Sinopharm or heterologous primary schemes might provide better protection against death; this effect might last longer in individuals aged ≥50 than homologous boosters. Funding: None