CDC studies look at COVID-19 vaccine booster effectiveness, safety

During the omicron wave, the Pfizer or Moderna COVID-19 vaccine was 87% effective at preventing emergency and urgent care visits and 95% effective at preventing hospitalizations in adults who received a third dose in the prior two months, according to a study released Friday by the Centers for Disease Control and Prevention. A third dose was more effective than a second dose but less effective over time, the study found. 

In a separate study reported Friday, adverse reactions were less frequent after a third dose than a second dose in adults who received the same COVID-19 vaccine for all their doses.