COVID-19 vaccine booster doses provide increased protection against COVID-19 hospitalization compared with previously vaccinated individuals: Interim findings from the REFORCO-Brazil real-world effectiveness study during Delta and Omicron

Wilhelmine Meeraus; Anke L Stuurman; Ilgaz Durukal; Eduardo Conde-Sousa; Andrew Lee; André Santa Maria; Bárbara Emoingt Furtado; Mario Ouwens; Christen M Gray; Douglas Andreas Valverde; Hugo Gomes da Silva; Sylvia Taylor

doi:10.1016/j.vaccine.2023.08.085

COVID-19 vaccine booster doses provide increased protection against COVID-19 hospitalization compared with previously vaccinated individuals: Interim findings from the REFORCO-Brazil real-world effectiveness study during Delta and Omicron

Vaccine. 2023 Oct 6;41(42):6366-6378. doi: 10.1016/j.vaccine.2023.08.085. Epub 2023 Sep 12.

Affiliations

¹ Medical Evidence, Vaccines & Immune Therapies, AstraZeneca, Cambridge, UK. Electronic address: wilhelmine.meeraus@astrazeneca.com.
² Medical Evidence, Vaccines & Immune Therapies, AstraZeneca, Cambridge, UK; P95 Epidemiology & Pharmacovigilance, Leuven, Belgium.
³ Real World Science, BioPharmaceuticals Medical, AstraZeneca, Cambridge, UK.
⁴ Medical and Payor Statistics, BioPharmaceuticals Business Unit, AstraZeneca, Cambridge, UK.
⁵ Evidence Generation, AstraZeneca, São Paulo, Brazil.
⁶ Vaccines & Immune Therapies, BioPharmaceuticals Medical, AstraZeneca, São Paulo, Brazil.
⁷ Medical and Payor Statistics, BioPharmaceuticals Business Unit, AstraZeneca, Mölndal, Sweden.
⁸ Techtrials Healthcare Data Science, São Paulo, Brazil.
⁹ Formerly BioPharmaceuticals Medical, AstraZeneca, Cambridge, UK.
¹⁰ Medical Evidence, Vaccines & Immune Therapies, AstraZeneca, Cambridge, UK.

PMID: 37704499
DOI: 10.1016/j.vaccine.2023.08.085

Abstract

Background: Although COVID-19 booster vaccination is widely recommended, there is limited long-term, population-level, real-world evidence on the magnitude of improved protection against severe COVID-19 conferred by boosting with monovalent COVID-19 vaccines developed against ancestral SARS-CoV-2, especially in low- or middle-income countries. We present interim results from the first large-scale assessment of the relative vaccine effectiveness (rVE) of first and second booster doses against severe COVID-19 in a low-/middle-income country.

Methods: REFORCO-Brazil is an ongoing, test-negative case-control study (NCT05697705) utilizing Brazil national severe acute respiratory syndrome (SARS) surveillance and vaccination data. In SARS hospitalizations from August 1, 2021 to July 31, 2022, we matched test-positive (via SARS-CoV-2 antigen/reverse transcription polymerase chain reaction [RT-PCR]) cases and test-negative case-controls (via RT-PCR) based on admission date, preceding vaccinations, and age. We evaluated the rVEs of four monovalent COVID-19 vaccines (AZD1222, Ad26.COV2.S, CoronaVac, and BNT162b2) as second boosters compared with any first boosters received ≥4 months previously, and as first boosters compared with primary-series vaccinations completed ≥4 months previously.

Results: The overall rVE of second boosters, from 5668 (2238 test-positive) evaluated hospitalizations, was 24.7 % (95 % confidence interval [CI]: 12.6-35.1); the overall rVE of first boosters, from 30,272 (12,063 test-positive) hospitalizations, was 46.8 % (95 % CI: 43.3-50.0). The rVEs of AZD1222 and BNT162b2 were similar: 29.4 % (95 % CI: 8.6-45.5) and 25.5 % (95 % CI: 4.2-42.2), respectively, for second boosters; and 42.5 % (95 % CI: 28.0-54.0) and 50.8 % (95 % CI: 47.5-54.0), respectively, for first boosters. In general, rVEs were higher in elderly (≥80 years) and immunocompromised/high-risk individuals.

Conclusions: Our results support the use of AZD1222 and other adenoviral/mRNA vaccine boosters to maintain protection against COVID-19 hospitalization from Omicron subvariants, including in elderly and immunocompromised individuals at increased risk of accelerated waning or severe outcomes.

Keywords: COVID-19; First booster; Hospitalisation; Omicron; Relative vaccine effectiveness; Second booster.