According to the Associated Press, experts say that any highly transmissible variant—including Omicron—is unlikely to lead to herd immunity in the United States. Dr. Don Milton of the University of Maryland School of Public Health commented: "Herd immunity is a vague concept that does not apply to SARS-CoV-2."

Herd immunity occurs when a sufficient proportion of a population has immunity to a virus, making it difficult for the virus to spread to those unprotected by vaccination or prior infection. For measles, herd immunity requires approximately 95% of the community to be immune.

Early hopes for COVID-19 herd immunity have been dashed for several reasons. First, antibodies from vaccination or prior infection wane over time. While vaccines provide strong protection against severe disease, waning antibodies mean breakthrough infections remain possible—even in boosted individuals. Second, there are vast global disparities in vaccination coverage: in some low-income countries, less than 5% of the population is vaccinated. Third, vaccine hesitancy persists in many developed countries. Fourth, young children remain ineligible for vaccination in many places.

As long as the virus continues to spread, it will mutate, generating new variants that increasingly evade protection from vaccines or prior infection. Dr. Milton suggests populations are moving toward "herd resistance" —a scenario where infections continue, but people have sufficient protection so that future outbreaks will not cause societal disruption. Many scientists believe COVID-19 will eventually become like influenza, causing seasonal outbreaks without massive surges.