This week marks two years since the U.S. began distributing and administering COVID vaccines.

A new study estimates how much worse the pandemic might have been without them.

Computer-modeling-based research by the Commonwealth Fund suggests that vaccines have reduced COVID's potential death toll by more than 3 million, reduced medical costs by $1 trillion and kept kids in school longer.

Without vaccines, the country would have seen 1.5 times more infections and 3.8 times more hospitalizations since December 2020, increasing the odds of long COVID and of reinfections, which have higher risk of death.

Even in evasive variants like omicron, vaccines blunted disease severity, lessening the burden on hospitals even as high rates of flu and RSV now strain the healthcare system.