According to researchers, the risk of contracting COVID-19 during the Omicron wave was higher if the index case was unvaccinated, but it was still high among vaccinated cases.

A study published in the Morbidity and Mortality Weekly Report suggests that among index cases who had not received a COVID-19 vaccine, the attack rate in household contacts was 64%, compared to 44% in contacts of index cases who had received their full primary vaccination series within 5 months, and 43% among those who were vaccinated and had also received a booster.

Additionally, the attack rates were lower when index cases isolated or wore a mask at home. Among household contacts of index patients who underwent isolation, the attack rate was 41%, compared to 68% for those who did not undergo isolation (P<0.01). The attack rates were 40% for contacts of index cases who ever wore a mask at home at the time when they were potentially infectious, compared to 69% for those who reported never wearing a mask at home (P<0.01)… (Medpage Today)