News Scan for Jun 01, 2022

3 doses of same, different vaccines protect against mild, severe COVID-19Three COVID-19 vaccine doses offer good protection against infection and hospitalization, including those caused by variants of concern—regardless of brand, type, or combination, according to an ongoing meta-analysis published yesterday in BMJ.Researchers from the Chinese University of Hong Kong searched 38 World Health Organization (WHO) databases each week for studies on the efficacy of regimens using the same (homologous) COVID-19 vaccine or a combination (heterologous) of types, with or without a third dose, starting on Mar 8, 2022.The analysis included 53 observational studies and randomized controlled trials involving 100,190,476 participants of all ages given a total of 24 different COVID-19 regimens using seven vaccine types.A three-dose mRNA vaccine regimen was the most effective against both symptomatic and asymptomatic infections, with an estimated effectiveness of 96% (95% credible interval [CrI], 72% to 99%).

A combination of two doses of adenovirus vaccines with one dose of mRNA vaccine had an estimated efficacy of 88% (95% CrI, 59% to 97%).Estimated effectiveness of two doses of the same mRNA vaccine was 99% (95% CrI, 79% to 100%) against severe COVID-19.

Three doses of an mRNA vaccine offered the most protection against COVID-19 hospitalization, at 95% (95% CrI, 90% to 97%), but their effectiveness against death was uncertain because of confounding factors and the observational nature of the eight studies reporting deaths.Subgroup analyses showed that a three-dose vaccine regimen was comparably effective in all age-groups, including people 65 and older, as well as in those with impaired immune systems—even against infections caused