Effectiveness of homologous and heterologous boosters after primary regimens with Sputnik V, AstraZeneca, and Sinopharm during the omicron variant period in adults over 50 years old in the province of Buenos Aires

Abstract

Objective: To evaluate the effectiveness of primary vaccination regimens involving Sputnik V, Astra-Zeneca, Sinopharm, or heterologous combinations followed by viral vector boosters (Sputnik V, As-traZeneca) or mRNA boosters (Pfizer-BioNTech, Moderna) against infections, hospitalizations and deaths caused by SARS-CoV-2. Material and methods: Case-control studies with negative tests conducted in the Buenos Aires province during the Omicron BA.1 predominance. The study included patients ≥ 50 years of age, who tested positive for SARS-CoV-2 and had received two or three doses of vaccines. Infections, hospitalizations, and deaths were registered following the administration of Sputnik V, AstraZeneca, or mRNA boosters. Findings: Out of 422 124 people tested for SARS-Cov-2, 221 993 (52.5%) had positive test results; 190,884 (45.2%) and 231 260 (54.8%) received two-dose and three-dose vaccination schemes, respectively. Primary regimens with AstraZeneca, Sputnik V, or viral vector, combined with a viral vector booster demonstrated protection against infections (OR 0.94 [0.92 to 0.97]), hospitalizations (OR 0.30 [0.26 to 0.35]) and deaths (OR 0.29 [0.25 to 0.33]. Primary regimens with AstraZeneca and Sputnik V combined with mRNA boosters, as well as pri-mary schemes with Sinopharm combined with mRNA or viral vectored boosters showed additional protection against infections (OR 0.70 [0.68 to 0.71]). There was a protective effect against hospi-talizations and deaths (OR 0.26 [0.22-0.31] and 0.22 [0.18 -0.25]) in all cases. Conclusions: During Omicron predominance, heterologous boosters with viral-vector and mRNA vaccines, administered after Sputnik V, AstraZeneca, Sinopharm, or heterologous primary regimens, could provide enhanced protection and prolonged effectiveness against mortality in individuals aged ≥ 50, compared to ho-mologous boosters.