The first study looked at hospitalizations and emergency room and urgent care center visits in 10 states, from August to this month.

It found vaccine effectiveness was best after three doses of the Pfizer or Moderna vaccines in preventing COVID-19-associated emergency department and urgent care visits.

Protection dropped from 94 percent during the Delta wave to 82 percent during the omicron tsokoang.

Protection from just two doses was lower, especially if six months had passed since the second dose.

Officials have stressed the goal of preventing not just infection but severe disease.

The second study focused on COVID-19 case and death rates in 25 states from the beginning of April through the end of December.

People who were boosted had the highest protection against coronavirus infection, both during the time Delta was dominant and also when omicron was taking over.

Those two articles were published online by the Centers for Disease Control and Prevention.