Chilean researchers found that a different type of vaccine (heterologous) worked better than the same type of vaccine (homologous) when the third “booster shot” was given.
Chilean researchers recently presented new results from Chile’s COVID-19 vaccination program at the European Congress of Clinical Microbiology and Infectious Diseases (Lisbon, Portugal, April 23-26). They found that a different type of vaccine (heterologous) worked better than the same type of vaccine (homologous) when the third “booster shot” was given.
This study was also published in The Lancet Global Health on April 23, 2022.
This study evaluated the efficacy of a booster shot of the CoronaVac (Kexing Bio), AZD1222 (Oxford/AstraZeneca) and BNT162b2 (Pfizer/BioNTech) vaccines in subjects who had completed two doses Sinovac vaccinated individuals. The study also assessed Chile’s national vaccination program, with two doses of the Sinovac vaccine being by far the most common.
Investigators evaluated individuals who were vaccinated between February 2, 2021 and November 10, 2021, while excluding individuals who had been infected with the new coronavirus or who had been vaccinated before then . They predicted the effectiveness of boosting for symptomatic COVID-19 cases and COVID-19 outcomes (hospitalization, ICU admission, and death).
A total of 11.17 million people were eligible for this study, of whom 4.13 million completed two doses of the Sinovac vaccine and received a booster dose during the study. Of these, 1.92 million participants (46.5%) received a heterologous AZD1222 booster, 1.87 million (48.9%) received a heterologous BNT162b2 booster, and nearly 190,000 (4.5%) received Sinovac’s Homologous booster needles.
The authors calculated that the two-dose vaccine plus the Kexing booster was 79% effective in preventing symptomatic COVID-19, the BNT162b2 booster was 97%, and the AZD1222 booster was 93% effective . The efficacy of Sinovac booster against COVID-19-related hospitalization, ICU admission and death was 86%, 92%, and 87%, respectively, 96%, 96%, and 97% for BNT162b2 booster, and 98%, 99% for AZD1222 booster % and 98%.
The authors explain that booster programs have been launched in countries due to emerging evidence of weakened immunity with the two-dose regimen. Boosters are also important because there is evidence that inactivated vaccines are less protective than Pfizer/BioNTech and Moderna’s mRNA vaccines. During the study period, the predominant Covid-19 strain in Chile was the Delta strain.
They concluded: “Our results show that a third booster dose provided a high level of protection against COVID-19 in people who had previously received two doses of Sinovac vaccine, including Serious illness and death…however, different booster shots were more effective than the same booster shots, which provided additional support for vaccine mixes.”
The authors further explain that this is one of the first studies to examine the effectiveness of booster shots of the inactivated SARS-CoV-2 vaccine. A recent study in Brazil showed that both homologous and heterologous boosters (BNT162b2 and AZD1222) were safe and immunogenic after completion of two doses of Sinovac vaccine. Likewise, a US study of boosters for mRNA-1273, Ad26.COV2.S, and BNT162b2 found that a heterologous booster was more immunogenic than a homologous booster.
A Phase 2 Cov-Boost study in the UK shows that each vaccine is safe and immunogenic as a booster after two doses of AZD1222 and BNT162b2 , while the antibody level reached the highest level after inoculation with the mRNA booster.
In Chile, the government now recommends preference for heterologous boosters; however, homologous boosters can be administered as an alternative.
References
Effectiveness of homologous and heterologous booster doses for an inactivated SARS-CoV-2 vaccine: a large-scale prospective cohort study
Source: Biotech