Population-wide study of COVID-19 vaccination shows that mix-and-match approach to booster vaccination offers the best protectionRead Now
A new study on Chile’s national COVID-19 vaccination program, to be presented at this year’s European Congress of Clinical Microbiology & Infectious Diseases (ECCMID 2022, Lisbon 23-26), and published in The Lancet Global Health, shows that giving a different type of vaccine (heterologous) for the third or ‘booster’ dose than was received for the first two doses, leads to better vaccine performance than using the same (homologous) inactivated SARS-CoV-2 vaccine for all three doses.
The study is by Dr Rafael Araos, Institute of Science and Innovation in Medicine, Clinica Alemana, Universidad del Desarrollo, Dr Alejandro Jara, and Dr Eduardo A Undurraga from Pontificia Universidad Católica de Chile, and colleagues including Dr Johanna Acevedo from the Chilean Ministry of Health.
The study assesses the effectiveness of CoronaVac (Sinovac Biotech), AZD1222 (Oxford-AstraZeneca), or BNT162b2 (Pfizer-BioNTech) vaccine boosters in individuals who had completed a primary two-dose immunisation schedule with CoronaVac, an inactivated SARS-CoV-2 vaccine which accounts for about half the COVID-19 vaccine doses delivered globally, compared with no vaccination. The study assessed the nationwide vaccination program in Chile, where the two-dose Coronavac schedule was by far the most commonly given.
Individuals administered vaccines from Feb 2, 2021 to the prespecified trial end date of Nov 10, 2021 were evaluated; the team excluded individuals with a probable or confirmed SARS-CoV-2 infection (RT-PCR or antigen test) on or before Feb 2, 2021, and individuals who had received at least one dose of any COVID-19 vaccine before Feb 2, 2021. They estimated the vaccine effectiveness of booster doses against laboratory-confirmed symptomatic COVID-19 (symptomatic COVID-19) cases and COVID-19 outcomes (hospitalisation, admission to the intensive care unit [ICU], and death).
A total of 11 174 257 individuals were eligible for this study, among whom 4 127 546 completed a primary immunisation schedule (two doses) with CoronaVac and received a booster dose during the study period. 1 921 340 (46·5%) participants received a heterologous AZD1222 booster, 2 019 260 (48·9%) received a heterologous BNT162b2 booster, and 186 946 (4·5%) received a homologous booster with CoronaVac.
The authors calculated an adjusted vaccine effectiveness (using statistical modelling) in preventing symptomatic COVID-19 of 79% for a two-dose schedule plus CoronaVac booster, 97% for a BNT162b2 booster, and 93% for an AZD1222 booster. The adjusted vaccine effectiveness against COVID-19-related hospitalisation, ICU admission, and death was 86%, 92%, and 87% for a CoronaVac booster, 96%, 96%, and 97% for a Pfizer-BioNTech booster, and 98%, 99% and 98% for an Astra Zeneca booster.
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