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The COVID-19 mRNA vaccines’ 2-dose primary series appeared to provide less protection against hospitalization from Omicron variant infections than Alpha and Delta infections, according to a recent study. A booster dose, however, was associated with increased effectiveness against Omicron hospitalizations at the same high levels achieved against earlier variants with 2 doses.
The study included data from 11 690 adults admitted to 21 US hospitals from March 11, 2021, to January 14, 2022, about half of whom had laboratory-confirmed COVID-19. The other half served as a control group. To calculate vaccine effectiveness, researchers compared the odds of vaccination between the 2 groups. In the COVID-19 group, SARS-CoV-2 variants were determined using whole-genome sequencing or were classified based on the predominant variant at the time of hospitalization. Sequencing results were available for 45.4% of the 5728 SARS-CoV-2 infections.
The effectiveness of 2 vaccine doses against hospitalization was 85% during the periods of the study when Alpha and Delta dominated but 65% during the Omicron period—late December 2021 through mid-January 2022. The effectiveness of 3 vaccine doses during the Omicron phase was 86%.
Regardless of which strain was circulating at the time, COVID-19 severity, based on the World Health Organization clinical progression scale, was lower for vaccinated than for unvaccinated patients. Vaccination, including 2 or 3 doses, was 76% effective for preventing progression to invasive mechanical ventilation or death with the Alpha variant and around 45% effective with Delta or Omicron infections. The findings appeared in the BMJ.
Créditos: Comité científico Covid