The earliest data on vaccine efficacy against Omicron is reflected in data from South Africa and the United Kingdom, where those with two doses of an mRNA vaccine show efficacy against infection down to around 35%. (Delta had taken such mRNA vaccines down from the 90% level to around 60-70%.) The booster takes the 35% figure up to around 75%.
In the United States, vaccines have had an efficacy against hospitalization for those with two doses in the 80-90% range, by a variety of data sampling throughout the first eleven months of 2021. The unvaccinated are five times more likely to test positive than the vaccinated, and fourteen times more likely to die. Compared to those with boosters, they are ten times more likely to test positive, seventeen times more likely to be hospitalized, and twenty times more likely to die.
