CDC research documents vaccination efficacy trends among front-line health care workers, Los Angeles COVID-19 infections and hospitalizations

The Centers for Disease Control and Prevention today released research highlighting two important trends emerging from the COVID-19 pandemic regarding vaccines’ current effectiveness. The first, which looked at breakthrough infections among fully vaccinated front-line health care workers, found that, following the emergence of the SARS-CoV-2 delta variant, there has been a moderate reduction in the effectiveness of COVID-19 vaccines in preventing infection in this group. However, the authors note that “this trend should be interpreted with caution because [vaccine efficacy] might also be declining as time since vaccination increases and because of poor precision in estimates due to limited number of weeks of observation and few infections among participants.” Additionally, the CDC notes that even a sustained two-thirds reduction in infection risk underscores COVID-19 vaccinations’ continued importance and benefits in preventing deaths, hospitalizations and the virus’ spread. 
  
The second study reviewed SARS-CoV-2 infections in Los Angeles County over the course of nearly three months, starting in May 2021. Researchers found that approximately three out of four cases were among unvaccinated individuals. Additionally, infection and hospitalization rates among unvaccinated persons were 4.9 and 29.2 times more likely, respectively, than those in fully vaccinated persons, with little change when the delta variant took root as the nation’s dominant virus strain.