Preprints with The Lancet is part of SSRN´s First Look, a place where journals identify content of interest prior to publication. Authors have opted in at submission to The Lancet family of journals to post their preprints on Preprints with The Lancet. The usual SSRN checks and a Lancet-specific check for appropriateness and transparency have been applied. Preprints available here are not Lancet publications or necessarily under review with a Lancet journal. These preprints are early stage research papers that have not been peer-reviewed. The findings should not be used for clinical or public health decision making and should not be presented to a lay audience without highlighting that they are preliminary and have not been peer-reviewed. For more information on this collaboration, see the comments published in The Lancet about the trial period, and our decision to make this a permanent offering, or visit The Lancet´s FAQ page, and for any feedback please contact email@example.com.
Effectiveness of Homologous and Heterologous Booster Shots for an Inactivated SARS-CoV-2 Vaccine: A Large-Scale Observational Study
20 Pages Posted: 13 Jan 2022More...
Background: Vaccine protection against Covid-19 may be waning. Several countries have authorized or begun using a booster vaccine dose. Policymakers urgently need evidence of the effectiveness of additional vaccine doses against Covid-19 and its clinical spectrum for individuals with complete primary immunization schedules.
Methods: We used a prospective national cohort of 11·2 million persons 16 years or older to assess the effectiveness of CoronaVac, AZD1222, or BNT162b2 vaccine boosters in individuals who completed their primary immunization schedule with CoronaVac compared to unvaccinated individuals. The study was conducted in Chile from February 2 through November 10, 2021. We used inverse probability-weighted survival regression models to estimate hazard ratios, accounting for time-varying vaccination status and adjusting for relevant demographic, socioeconomic, and clinical confounders. We estimated the change in the hazard associated with complete immunization (≥14 days after the booster).
Findings: We found an adjusted vaccine effectiveness against symptomatic Covid-19 of 78·8% (95% confidence interval, CI, 76·8–80·6) for a three-dose schedule with CoronaVac, 96·5% (95% CI, 96·2–96·7) for BNT162b2 booster, and 93·2% (95% CI, 92·9–93·6) for the AZD1222 booster. The adjusted vaccine effectiveness against hospitalization, ICU admission, and Covid-19 related deaths was 86·3%, 92·2%, and 86·7% for a three-dose schedule with CoronaVac, 96·1%, 96·2%, and 96·8% for the BNT162b2 booster, and 97·7%, 98·9%, and 98·1% for the AZD1222 booster.
Interpretation: Our results suggest that a homologous or heterologous booster shot for individuals with a complete primary vaccination schedule with CoronaVac provides a high level of protection against Covid-19, including severe disease and death. However, heterologous boosters showed higher vaccine effectiveness for all outcomes, providing additional support for using a mix and match approach.
Funding Information: Agencia Nacional de Investigación y Desarrollo (ANID) Millennium Science Initiative Program and Fondo de Financiamiento de Centros de Investigación en Áreas Prioritarias (FONDAP).
Declaration of Interests: The authors declare no conflicts of interest.
Ethics Approval Statement: The research protocol was approved by the Comité Ético Científico Clínica Alemana Universidad del Desarrollo. The study was considered exempt from informed consent, no human health risks were identified. Research analysts belong to the Chilean Ministry of Health; our use of data follows Chilean law 19·628 on personal data protection.
Keywords: SARS-CoV-2, COVID-19, vaccine effectiveness, inactivated SARS-CoV-2 vaccine, immunization program, boosters.
Suggested Citation: Suggested Citation