For most of this year, the rolling average for the number of covid-19 vaccinations administered each day in the U.S. has been trending downward. But that changed recently.
For eight consecutive days ending Friday, the last day for which data is available, the average number of vaccinations administered more than doubled to 485,505 a day Friday from 214,405 a day March 30, according to data from the Centers for Disease Control and Prevention.
The bulk of the recent vaccinations were booster doses, data shows.
While there is no certain explanation for the noticeable jump in shots, the daily increases came after federal regulators authorized second booster shots of the Pfizer and Moderna vaccines late last month for everyone 50 and older who had received their first booster shots at least four months earlier.
Those 12 and older with certain immune deficiencies were also authorized to receive a second booster, the Food and Drug Administration said.
The decision meant that tens of millions of Americans have become eligible for their fourth vaccine shots just as the country is dealing with a highly contagious omicron subvariant, known as BA.2, which caused cases to rise in Europe and which is now the dominant version of the virus in new U.S. cases.
Although caseloads nationally have been relatively low in recent weeks, BA.2 is contributing to an increase in cases in some places, especially in the Northeast.
Public health researchers say it's likely that older Americans seeking extra shots are driving the vaccination surge.
"Data from other countries currently experiencing BA.2 surges suggests that second boosters will make a meaningful impact in protecting vulnerable individuals," said Bertha Hidalgo, an associate professor of epidemiology at the University of Alabama at Birmingham.
The World Health Organization is keeping an eye on two new strains of covid-19 that have popped up around the world.
WHO scientists are looking into the BA.4 and BA.5 strains, subvariants of omicron, because of their "additional mutations that need to be further studied to understand their impact on immune escape potential," the organization said Monday.
Last week, the UK Health Security Agency said BA.4 had been traced in South Africa, Scotland, England, Botswana and Denmark between Jan. 10 to March 30. All BA.5 cases have been reported in South Africa.
Of those, all were in people between the ages of 30 and 50 who were fully vaccinated and said they were experiencing only mild symptoms.
But the WHO said only a "few dozen" cases have been registered into the global database so far.
COLLEGES REVISTING MASKS
A small number of U.S. colleges and universities are reinstating mask policies, citing coronavirus outbreaks on campus.
As of Sunday, there were an average of more than 31,000 new cases across the country, according to a New York Times database, a 3% increase over the past two weeks. New York City and Washington, D.C., have seen sharper increases, although the average number of cases remains a fraction of each city's peak.
Amid the winter surge driven by another form of omicron, some universities shifted to enacting school policies aimed at living with the virus, such as quarantining and social distancing when outbreaks occur, rather than canceling instruction altogether.
As new cases decreased, some colleges and universities further loosened precautions despite criticism from public health experts. But now, while some universities, such as Harvard, are letting professors decide what protocol to follow in the classroom, others are imposing new mask rules.
Rice University in Houston reinstated its mask policy for classrooms, regardless of vaccination status. Those who are unvaccinated also must continue to wear a mask in other indoor areas.
PHILADELPHIA REINSTATES MASK MANDATE
Philadelphia became the first major U.S. city to reinstate its indoor mask mandate on Monday after reporting a sharp increase in coronavirus infections, with the city's top health official saying she wanted to forestall a potential new wave driven by BA.2.
Confirmed covid-19 cases have risen more than 50% in 10 days, the threshold at which the city's guidelines call for people to wear masks indoors, said Dr. Cheryl Bettigole, the health commissioner.
"If we fail to act now, knowing that every previous wave of infections has been followed by a wave of hospitalizations, and then a wave of deaths, it will be too late for many of our residents," said Bettigole, noting about 750 Philadelphia residents died in the wintertime omicron outbreak. "This is our chance to get ahead of the pandemic, to put our masks on until we have more information about the severity of this new variant."
Health inspectors will begin enforcing the mask mandate at city businesses on April 18.
Philadelphia ended its indoor mask mandate March 2, and Bettigole acknowledged "it was wonderful to feel that sense of normalcy again."
Confirmed cases have since risen to more than 140 per day -- still a fraction of what Philadelphia saw at the height of the omicron surge -- while hospitalizations remain low at only 46 patients.
Information for this article was Eduardo Medina and Giulia Heyward of The New York Times, by Kate Feldman of New York Daily News (TNS), Michael Rubinkam and Michelle L. Price of The Associated Press.