Two other factors provide reassurance despite BA.2’s transmissibility. One is that it does not cause more severe disease as compared to the original omicron strain, known as BA.1, which is a milder variant than some previous strains such as delta. The other is that BA.2 is not so substantially different from BA.1 that it escapes immunity from vaccines or prior infection. A New England Journal of Medicine paper reported that people with booster doses produced equally effective antibodies against BA.1 as BA.2. And researchers from Britain and Qatar have found that vaccines provide excellent protection against severe illness due to both omicron subvariants.

Furthermore, people who were previously infected with omicron are unlikely to be reinfected with BA.2. A preprint study from Denmark found only 47 instances of BA.2 reinfection following infection of the original omicron strain, out of more than 1.8 million recent cases of covid-19.

On a population level, the combination of recovery from omicron and vaccination means that the United States has high rates of immunity against BA.2. The influential Institute for Health Metrics and Evaluation has estimated that as many as 80 percent of Americans have some immunity that will protect them against a new omicron wave. This may be enough to successfully decouple infection from hospitalization such that a rise in cases does not overwhelm hospitals.