The odds that vaccinated people will catch the virus if a household member becomes infected are nearly three to four times higher with Omicron than with Delta, but booster doses reduce that risk, new findings suggest.
Researchers analyzed transmission data collected from nearly 12,000 infected households in Denmark, including 2,225 households with an Omicron infection.
Overall, there were 6,397 secondary infections in the week after the first infection in the house. After accounting for other risk factors, the rate of person-to-person spread of the virus to fully vaccinated people was roughly 2.6 times higher in Omicron households than in Delta households, the researchers reported on this week on medRxiv ahead of peer review.
Booster-vaccinated people were nearly 3.7 times more likely to get infected in the Omicron households than in the Delta households, they found.
Looking only at Omicron households, however, booster-vaccinated people were 56% less likely to become infected compared to vaccinated people who had not received a booster. And overall, when booster-vaccinated people were the ones who first brought home the virus, they were less likely than unvaccinated and vaccinated-but-not-boosted people to pass it to others.