In a sign of growing concern among federal health officials about the spread of new coronavirus infections, the Centers for Disease Control and Prevention is now saying that all people 50 or older should get a second booster shot if at least four months have passed since their first booster dose.
Previously, the agency said those 50 and older had the option of the additional shot, but only encouraged people over 65 or with underlying medical conditions to get it. The new guidance, issued in a statement on the C.D.C.’s website on Thursday, also extends to anyone 12 and older with certain immune deficiencies.
The C.D.C. said it was changing its advice because of a steady rise in infections over the past month, coupled with “a steep and substantial increase in hospitalizations for older Americans.” New confirmed cases surpassed an average of 100,000 a day again this week, according to a New York Times database — a number considered an undercount. And nationally, hospitalizations of people with Covid-19 were averaging more than 23,800 a day as of Thursday, 31 percent more than two weeks ago.
Most Americans 50 or older received their last dose of Covid vaccine more than six months ago. That has left “many who are vulnerable without the protection they may need to prevent severe disease, hospitalization and death,” the C.D.C. said.
In another warning of growing Covid risks, Dr. Rochelle P. Walensky, the agency’s director, said Friday that more that 45 percent of Americans now live in areas where transmission rates are high enough that they should at least consider wearing a mask in indoor public settings.
That was a substantial jump from the data she cited just two days earlier at a White House briefing. She said then that about one-third of Americans lived in counties with medium to high levels of virus transmission. That itself was a big increase; only about one-fourth of the population fell into risk zones the previous week, she said.
In a message posted Friday on Twitter, Dr. Walensky said those in high-risk areas — largely in the Northeast — should wear masks indoors in public. Those in medium-risk areas, which include counties in nearly every state, should consider masks based on their assessment of their personal risks, she said.
Hospital admissions of patients with Covid are a major factor in the C.D.C.’s assessments of a community’s risk. But other experts cautioned that hospitalization data could be misleading because patients might have been admitted for unrelated illnesses, and merely tested positive during routine Covid checks.
“We have 11 people in our hospital right now with Covid,” said Dr. Monica Gandhi, an infectious disease doctor at San Francisco General Hospital. “Three of them were hospitalized for Covid and the other eight have Covid in their noses and are there for other reasons.”
She said that in Massachusetts, a state with a high rate of vaccination, officials estimate that as many as 70 percent of hospital patients who test positive for the virus were admitted primarily for unrelated illnesses. However, coronavirus infections can also exacerbate underlying medical conditions, which many Americans have.
The death rate from Covid, although a lagging indicator, may be a more reliable gauge of the degree of the disease’s impact, because physicians must note the cause of death on the death certificate, according to Dr. Gandhi and other experts.
Recently, deaths have remained low. About 275 deaths have been recorded each day on a seven-day average, Dr. Walensky said on Thursday. The number of new deaths has actually dipped slightly in recent weeks. According to the Times database, the overall toll of U.S. deaths surpassed one million on Thursday, the highest confirmed total of any nation.
Those age 50 or older have been eligible for a second booster since late March, but federal health officials have said too few people are taking advantage of it. Only one-fourth of those 65 and older who have gotten one booster dose, for instance, have gotten a second, the C.D.C.’s data show.
Dr. Walensky also said this week that the C.D.C. and the Food and Drug Administration were now discussing whether to broaden eligibility to those younger than 50.
This week, the agencies cleared a booster shot of the Pfizer-BioNTech vaccine for 5- to 11-year-olds, expanding eligibility for a first booster dose to a younger age group. Among other factors cited in its decision memo, the F.D.A. cited “the continued relaxation” of preventive measures, including mask mandates, social distancing and isolation of infected individuals.
The agency also noted the risk of long Covid, which it said “can cause significant morbidity after initially mild infection.”