3 doses of same, different vaccines protect against mild, severe COVID-19
Three 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 by the Alpha and highly transmissible Delta and Omicron variants.
The researchers said they recommend an mRNA vaccine booster to reinforce any primary vaccine regimen. "An mRNA booster can induce a similar level of protection against COVID-19 infections to homologous primary vaccination," they wrote. "A third dose [of] vaccine is needed to prevent COVID-19 variant infections."
May 31 BMJ study
Chest CT shows COVID-19 vaccines protect against pneumonia
According to research published yesterday in the American Journal of Roentgenology, chest computed tomography (CT) scans of adults fully vaccinated against COVID-19 were less likely to show pneumonia frequency and severity during breakthrough infections, compared to unvaccinated patients.
The data came from images collected at the University of Rome from 467 patients with a mean age of 65 who had chest CT scans from Dec 15, 2021, to Feb 18, 2022, while hospitalized for symptomatic COVID-19. In total 216 patients were unvaccinated, 167 were fully vaccinated with the Pfizer vaccine, and 84 were fully vaccinated with the AstraZeneca vaccine. Fully vaccinated was defined as at least 14 days from a second dose.
Only 15% of unvaccinated patients had scans absent of pneumonia, compared with 51% and 29% in patients fully vaccinated with Pfizer and AstraZeneca, respectively.
CT severity scores (CT-SS) also differed among the groups, with unvaccinated scored at an average of 9.7, compared with 5.2 for Pfizer and 6.2 for AstraZeneca).
"The visual observation by radiologic imaging of the protective effect of vaccination on lung injury in patients with breakthrough infections provides additional evidence supporting the clinical benefit of vaccination," the authors concluded.
May 31 AJR Am J Roentgenol study