Mix-and-match approach to booster shot offers best protection against COVID-19: Study

Giving a different vaccine as third dose than was received for first two shots les to better performance compared to using booster of same preventive, according to a study published in Lancet Global Health journal. research assessed effectiveness of CoronaVac, Pfizer and AstraZeneca vaccine boosters in individuals who h 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 COVID-19 vaccine doses delivered globally. researchers from Universid del Desarrollo, Pontificia Universid Catolica de Chile, and colleagues from Chilean Ministry of Health looked at Chile's national immunisation programme, where two-dose Coronavac schedule was by far most widely used.

Individuals ministered vaccines from February 2, 2021, to prespecified trial end date of November 10, 2021, were evaluated. researchers estimated vaccine effectiveness of booster doses against laboratory-confirmed symptomatic COVID-19 cases and COVID-19 outcomes -- hospitalisation, mission to intensive care unit (ICU), and death. A total of 11,174,257 (over 1 crore) individuals were eligible for this study, among whom 4,127,546 (over 41 lakh) completed a primary immunisation schedule (two doses) with CoronaVac and received a booster dose during study period.

As many as 1,921,340 (46·5 per cent) participants received an AstraZeneca booster, 2,019,260 (48·9 per cent) received a Pfizer booster, and 1,86,946 (4·5 per cent) received a CoronaVac third shot. researchers calculated an justed vaccine effectiveness in preventing symptomatic COVID-19 of 79 per cent for a two-dose schedule plus CoronaVac booster, 97 per cent for a Pfizer booster, and 93 per cent for an AstraZeneca booster.

vaccine effectiveness against hospitalisation, ICU mission, and death was 86 per cent, 92 per cent, and 87 per cent for a CoronaVac booster, 96 per cent, 96 per cent, and 97 per cent for a Pfizer booster, and 98 per cent, 99 per cent and 98 per cent for an AstraZeneca booster, y said.

"Our results suggest that a third dose of Coronavac or using a different booster vaccine such as Pfizer or AstraZeneca vaccines in those that h previously h two doses of Coronavac provides a high level of protection against COVID-19, including severe disease and death," authors of study noted.

"However, receiving a different vaccine for booster dose results in higher vaccine effectiveness than a third dose of Coronavac for all outcomes, providing ditional support for a mix-and-match approach," y said.

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 new mRNA technology vaccines from Pfizer and Moderna. Delta was predominant circulating variant in Chile during study period. A recent study in Brazil showed that homologous and heterologous booster vaccines following a CoronoVac primary vaccination schedule were safe and immunogenic, researchers said. Similarly, a phase 1-2 study in US with mRNA boosters found that heterologous boosters where on average more immunogenic than homologous boosters, y ded.