No, all COVID-19 vaccines have been effective at reducing the risk of severe illness. Getting a series of vaccine doses over an extended period of time – like months or years – is common for many vaccines. Healthcare providers recommend these vaccine series because over time the vaccine dose effect wanes and another dose is needed to restore optimal protection against new variants of a virus. The researchers who developed the COVID-19 vaccines continue to watch for waning immunity, how well the vaccines protect against new strains of the virus, and how that data differ across age groups and risk factors. This research has led to updated vaccines.

In the past, “boosters” have extended COVID-19 vaccine protection against serious illness, but they have been somewhat less effective in boosting immunity against new variants. The updated vaccine formula is designed to better target and protect against variants that currently account for most new infections.

Updated December 14, 2023