Reuters: Vaccine effectiveness against symptomatic infection from the Omicron variant of the coronavirus is likely to be much lower than against earlier variants, but they may still offer substantial protection against severe disease, a new analysis suggests.

Billy Gardner and Marm Kilpatrick from the University of California, Santa Cruz developed computer models incorporating data on COVID-19 vaccines’ efficacy against earlier variants and initial data on the Pfizer/BioNTech vaccine against Omicron. 

Their models suggest that early after two doses of an mRNA vaccine from Pfizer/BioNTech or Moderna, efficacy against symptomatic infection from Omicron is only about 30%, down from about 87% versus Delta, they reported on Sunday on medRxiv ahead of peer review. 

Protection against symptomatic infection is “essentially eliminated” for individuals vaccinated more than four months earlier. Boosters restore protection to about 48%, “which is similar to the protection of individuals with waned immunity against the Delta variant (43%),” Kilpatrick said.

“Importantly, protection against severe disease is much higher” for all categories: recently vaccinated, waned, or boosted. “We estimated that protection against severe disease was 86% for recent mRNA vaccination against Omicron, 67% for waned immunity, and 91% following third dose boosters,” Kilpatrick said. “There are still no direct estimates of vaccine effectiveness for severe disease from any country yet, so our estimates cannot be compared to direct estimates yet.”

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