Mix-and-match Of Booster Shots Offers Best Protection Against Covid-19, Says Study
Mixing different Covid-19 vaccines as the third dose than was received for the first two shots was found to be more effective than using the booster of the same preventive, a study published in The Lancet Global Health journal has said.
The study was conducted to determine the safety profile and effectiveness of mixing CoronaVac, Pfizer and AstraZeneca vaccine boosters in individuals who had a primary two-dose immunisation schedule with CoronaVac, compared with no vaccination.
CoronaVac is an inactivated SARS-CoV-2 vaccine which accounts for about half the COVID-19 vaccine doses delivered globally.
The researchers looked at Chile’s national immunisation programme, where the two-dose of Coronavac schedule was by far the most widely used.
The most important finding of the study was that receiving a different vaccine for the booster dose results in higher vaccine effectiveness than a third dose of Coronavac for all outcomes, providing additional support for a mix-and-match approach.
The researchers estimated the vaccine effectiveness of booster doses against laboratory-confirmed symptomatic COVID-19 cases and COVID-19 outcomes — hospitalisation, admission to the intensive care unit (ICU), and death.
The researchers calculated adjusted vaccine effectiveness in preventing symptomatic COVID-19 of 79% for a two-dose schedule plus CoronaVac booster, 97% for a Pfizer booster, and 93% for an AstraZeneca booster.
The study found vaccine effectiveness against hospitalisation, ICU admission, and death was 86%, 92%, and 87% for a CoronaVac booster, 96%, 96%t, and 97% for a Pfizer booster, and 98%, 99% and 98% for an AstraZeneca booster.
“Our results suggest that a third dose of Coronavac or using a different booster vaccine such as Pfizer or AstraZeneca vaccines in those that had previously had two doses of Coronavac provides a high level of protection against COVID-19, including severe disease and death,” the researchers said
A total of over 1 crore individuals were eligible for this study, among whom over 41 lakh completed a primary immunisation schedule (two doses) with CoronaVac and received a booster dose during the study period.
As many as 46·5% volunteers received an AstraZeneca booster, 48·9% received a Pfizer booster, and 4·5% received a CoronaVac third shot.
Booster programmes were initiated in various countries due to emerging evidence of waning immunity from two dose schedules. Boosters are also important because evidence suggests that inactivated vaccines like Coronavac offer lower protection than the new mRNA technology vaccines from Pfizer and Moderna.