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 study

Abstract

Objectives: To estimate the protection against laboratory-confirmed SARS-CoV-2 infection, hospitalisations, and death after homologous or heterologous third-dose (booster) in individuals with primary vaccination schemes with rAd26-rAd5, ChAdOx1nCoV-19, BBIBP-CorV or heterologous combinations, during the period of Omicron BA.1 predominance. Design: Retrospective, test-negative, case-control study, with matched analysis. Setting: Province of Buenos Aires, Argentina, between 12/1/21-4/1/21. Participants: 422,144 individuals ≥50 years who had received two or three doses of COVID-19 vaccines and were tested for SARS-CoV-2. Main outcome measures: Odds ratios of confirmed SARS-CoV-2 infection, hospitalisations and death after administering different boosters, compared to a two-dose primary scheme. Results: Of 221,933(52.5%) individuals with a positive test, 190,884(45.2%) had received a two-dose vaccination scheme and 231,260(54.8%) a three-dose scheme. The matched analysis included 127,014 cases and 180,714 controls. The three-dose scheme reduced infections (OR 0.81[0.80-0.83]) but after 60 days protection dropped (OR 1.04[1.01-1.06]). The booster dose decreased the risk of hospitalisations and deaths after 15-59 days (ORs 0.28[0.25-0.32] and 0.25[0.22-0.28] respectively), which persisted after administration for 75[66-89] days. Administration of a homologous booster after a primary scheme with vectored-vaccines provided low protection against infections (OR 0.94[0.92-0.97] and 1.05[1.01-1.09] before and after 60 days). Protection against hospitalisations and death was significant (OR 0.30[0.26-0.35] and 0.29[0.25-0.33] respectively) but decreased after 60 days (OR 0.59[0.47-0.74] and 0.51[0.41- 0.64] respectively). The inoculation of a heterologous booster after a primary course with ChAdOx1 nCoV-19, rAd26-rAd5, BBIBP-CorV, or heterologous schemes, offered some protection against infection (OR 0.70[0.68-0.71]), which decreased after 60 days (OR 1.01[0.98-1.04]). The protective effect against hospitalisations and deaths (OR 0.26[0.22-0.31] and 0.22[0.18-0.25] respectively) was clear and persisted after 60 days (OR 0.43[0.35-0.53] and 0.33[0.26-0.41]). Conclusions: This study shows that, during Omicron predominance, heterologous boosters provide an enhanced protection and longer effect duration against COVID-19-related hospitalisations and death in individuals older than 50, compared to homologous boosters.

Second Boost of Omicron SARS-CoV-2 S1 Subunit Vaccine Induced Broad Humoral Immune Responses in Elderly Mice

“…Therefore, the administration of additional heterologous boosters is recommended to enhance vaccine effectiveness and protect elderly people (13). It is crucial to develop strategies to improve vaccine effectiveness with alternative antigen sequences.…”

Estimation of Abortions in the Province of Buenos Aires, Argentina: a Bayesian Approach

“…In 2020, Buenos Aires Ministry of Health developed the first centralised registry of abortions, making it possible to have data to make direct estimates of them, as has been done in similar studies in other countries [12, 13]. Moreover, the information healthcare system proved to be robust enough for monitoring real-world vaccination campaigns [14, 15, 16, 17, 18, 19, 20]. This study made an estimate of the number of abortions produced during the year 2021 in the public health subsector and throughout the province, based on direct methods.…”