The CDC, in a real-world study, found the omicron Covid boosters are less than 50% effective against mild illness across almost all adult age groups when compared to people who are unvaccinated.
But people who received the boosters were better off than those who only got the old shots, with their protection increasing 28% to 56%.
The study did not look at hospitalization, but experts believe the shots will provide strong protection against severe outcomes.