The papers echo previous research — including studies in Germany, South Africa and the U.K.
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.
The second study focused on COVID-19 case and death rates in 25 states from the beginning of April through Christmas.
Three shots of the Pfizer and Moderna vaccines were about 67% effective against omicron-related symptomatic disease compared with unvaccinated people.