As COVID-19 infections rise in the U.S., a “significant proportion” of patients hospitalized with the virus are vaccinated but not boosted, according to Anthony Fauci, the nation’s top infectious disease expert.

“What we’re starting to see now is an uptick in hospitalizations among people who’ve been vaccinated but not boosted,” Fauci said Tuesday in an interview. “It’s a significant proportion,” he added, “but not the majority by any means.”

Dr. Rochelle Walensky, the director of the Centers for Disease Control and Prevention, echoed a similar sentiment on Wednesday, underscoring the importance of third shots for senior citizens.

“Although the highest risk are those people who are unvaccinated, we are seeing an increase in emergency department visits among adults 65 and older, which are now again higher than they are for younger age groups,” Walensky said Wednesday at a White House briefing. 

“The rate of disease is markedly lower for those who received their booster shot, demonstrating our boosters are working,” she said.

Public health experts have warned that the vaccines’ effectiveness wane over time, but protection is replenished with a booster shot.

NBC News reports:

Fauci pointed to data from Israel that show a major improvement in protection against severe disease and hospitalizations in those who have had boosters compared to those who haven’t. In a study published last month, Israeli researchers found a twentyfold reduction in severe disease among those over 60 who got booster shots. 

“That’s where we get back to the importance of getting a boost,” Fauci said. “It will dramatically diminish the likelihood that if you do get infected with a breakthrough infection that you’ll wind up in the hospital.” 

COVID-19 infections have risen 23% in the past two weeks, including in places with high vaccination rates, like Vermont. While there is an increase in the number of breakthrough incidents, the unvaccinated still make up the vast majority of cases.

ABC News reports:

Case rates in Vermont residents who are not fully vaccinated are nearly four times higher than in fully vaccinated residents, according to state data. Essex County, the least-vaccinated county in the state, is reporting the highest case rates of any county in Vermont, with 1,022 cases per 100,000 people reported from Nov. 2 to 8. In Grand Isle County, which has the highest vaccination rate in the state, that number was 160.

Statewide, those driving the surge include people in their 20s, who are the least vaccinated among Vermont adults, as well as children ages 5 to 11, who are just now eligible to get vaccinated, Dr. Mark Levine, Vermont’s health commissioner, said Tuesday.

About 30 million Americans – or 16% of those fully vaccinated – have received a booster shot, which are currently being offered to people 65 and older, the immunocompromised, those who live or work in settings with an increased risk of transmission, and original recipients of the Johnson & Johnson vaccine. According to The New York Times, the FDA and CDC might authorize boosters for all American adults as soon as this week.