This week, the Biden administration strongly recommended booster shots for most vaccinated Americans, and the Centers for Disease Control and Prevention also released three studies that federal officials said provided evidence that booster shots from the Pfizer-BioNTech and Moderna coronavirus vaccines would be needed in the coming months.
Here’s what we know about booster shots – why Americans might need them and when they should get them:
The case for a booster shot
Taken together, the CDC studies show that while the vaccines remain highly effective against hospitalizations and deaths, the bulwark they provide against infection with the virus has weakened in recent months.
The finding matches early data from seven states, collected this week by NewsMadura, and suggests an increase in breakthrough infections and a smaller increase in hospitalizations among those vaccinated as the Delta variant spread in July.
The decline in effectiveness against infection could be the result of declining vaccine immunity, the lapse of precautions like wearing masks or the emergence of the highly contagious Delta variant, experts said — or a combination of all three.
Overall, the new studies indicate that vaccines have an effectiveness of about 55 percent against all infections, 80 percent against symptomatic infection and 90 percent or more against hospitalization, noted Ellie Murray, an epidemiologist at Boston University.