COVID-19 vaccines 85% effective against hospital cases but weaken over time


A pair of new studies detail COVID-19 vaccine effectiveness, one showing 85% protection against hospitalization and the other describing waning efficacy for three vaccine types against infection and death caused by the highly transmissible Delta (B1617.2) variant among US veterans.

84% of hospitalizations in unvaccinated

The first study, published yesterday in JAMA, was led by researchers from the Centers for Disease Control and Prevention (CDC) COVID-19 Response Team.

It involved 4,513 hospitalized coronavirus patients at 21 sites in 18 US states from Mar 11 to Aug 15, 2021, with a 28-day follow-up period. The Delta variant became the predominant US strain in early July.

Of the 4,513 patients, 1,983 were diagnosed as having COVID-19, and 2,530 were uninfected controls. Median patient age was 59 years, 48.8% were women, 23.0% were Black, 15.9% were Hispanic, and 20.1% had an underlying medical condition.

Patients who received two doses of either the Pfizer/BioNTech or Moderna mRNA vaccine had an adjusted odds ratio (aOR) of 0.15 for hospitalization owing to COVID-19 versus an alternative diagnosis. Fully vaccinated COVID-19 hospital patients had an aOR of 0.33 for death or the need for invasive mechanical ventilation.



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