With a combination of vaccination and infections, the U.S. population now has a strong level of immunity against COVID-19.

Immune cells are able to produce effective antibodies that are trained to protect the body against future infections. When researchers looked at different booster shots, they found that they offered broad protection against different variants, such as the original strain, delta and omicron. One of the shots even recognized a variant that emerged after the vaccine was developed.

Vaccines have been credited to save more than 18 million hospitalizations and 3 million deaths in the United States, according to a report by The Commonwealth Fund. Over 80 percent of the U.S. population has received at least one dose of a COVID vaccine.

The new updated booster shot known as the bivalent vaccine is estimated to lower the risk of death by nearly half compared to those who did not receive it.