According to a study published in The Lancet Global Health Journal, giving a different vaccine than the third dose received for the first two shots has better performance than using a booster of the same preventive.
The research assessed the effectiveness of the CoronaVac, Pfizer and AstraZeneca vaccine boosters in individuals who had a primary two-dose vaccination schedule with CoronaVac compared to those without vaccination.
CoronaVac is an inactivated SARS-CoV-2 vaccine, which is about half the dose of the COVID-19 vaccine distributed globally.
Researchers from Universidad del Desarrollo, Pontificia Universidad Catolica de Chile and colleagues from the Chilean Ministry of Health looked at Chile’s national vaccination program, where the two-dose CoronaVac schedule was by far the most widely used.
Vaccinated individuals were assessed from February 2, 2021 to the scheduled trial end date of November 10, 2021.
Researchers estimate vaccine effectiveness of booster doses against laboratory-confirmed symptomatic COVID-19 cases and COVID-19 outcomes – hospitalization, intensive care unit (ICU) admission, and death.
A total of 11,174,257 (over 10 million) individuals were eligible for this study, of whom 4,127,546 (over 41 lakh) completed a primary vaccination program (two doses) with CORONAVAC and received a booster dose during the study period.
1,921,340 (465 percent) of participants received the AstraZeneca booster, 2,019,260 (489 percent) got the Pfizer booster, and 1,86,946 (45 percent) got the CoronaVac third shot.
Researchers calculated an adjusted vaccine effectiveness in preventing symptomatic COVID-19 of 79 percent for the two-dose schedule plus the CoronaVac booster, 97 percent for a Pfizer booster, and 93 percent for an AstraZeneca booster.
The vaccine effectiveness against hospitalization, ICU admission and death was 86 percent, 92 percent and 87 percent for the CoronaVac booster, 96 percent, 96 percent and 97 percent for the Pfizer booster, and 98 percent for the CoronaVac booster. 99 percent and 98 percent for the AstraZeneca booster, he said.
“Our results suggest that using a third dose of CoronaVac or a separate booster vaccine such as Pfizer or AstraZeneca, which previously contained two doses of CoronaVac, provides a high level of protection against COVID-19, including serious illness and death,” The study authors noted.
“However, 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,” he said.
Emerging evidence of reduced immunity from the two dosage schedules led to booster programs being introduced in various countries.
Boosters are also important because evidence suggests that inactivated vaccines such as CoronaVac offer less protection than vaccines from new mRNA technology from Pfizer and Moderna.
Delta was the major circulating version in Chile during the study period.
The researchers said a recent study in Brazil showed that domestic and heterogeneous booster vaccines were safe and immunosuppressive after the coronavirus primary vaccination program.
Similarly, a phase 1-2 study with mRNA boosters in the US found that heterologous boosters where on average more immunogenic than homologous boosters, he said.