COVID-19 vaccines protect against severe illness during Delta

A trio of studies in Morbidity and Mortality Weekly Report (MMWR) today show that COVID vaccines protect very well against the Delta (B1617.2) variant, with unvaccinated people having 5 times the risk of infection and more than 10 times the risk of hospitalization or death compared with vaccinated people.

Researchers analyzed data that included the period of Delta variant dominance in the United States, and their results indicate that the Pfizer/BioNTech, Moderna, and Johnson & Johnson vaccines all show strong vaccine effectiveness (VE) against severe COVID-19.

The new data join several studies published this week on high COVID-19 VE.

In the first of today’s studies, which looked at US incidence rate ratios (IRRs), the researchers found that, after Delta became the predominant strain, VE for full Pfizer or Moderna vaccination was 90% against hospitalization and 91% against death. But VE dropped from 91% to 78% for any adult COVID-19 infection during the Delta period.

While the IRR study’s 570,000-case cohort had a larger pool than the other MMWR studies, those two showed similar patterns. Both used test-negative designs, with a veterans-focused one suggesting a VE of 86.8% against COVID-19 hospitalization and a nine-state surveillance study suggesting a VE of 86% against hospitalization and 82% against emergency department (ED) and urgent care (UC) clinic visits.



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