The United States needs to expand its vaccination campaign going into the fall if the country is going to stem the nationwide surge of coronavirus cases driven by the delta variant, one of the federal government’s top health officials said Friday.

“I think that the prospects for the fall could be very challenging,” Rachel L. Levine, assistant secretary for health at the Department of Health and Human Services, said in a discussion hosted by The Washington Post. “However, if we are able to continue to ramp up our vaccination program, that’s the most important way to protect people in the fall.”

Levine’s remarks came as the Centers for Disease Control and Prevention on Friday published a sobering scientific analysis showing that vaccinated people can spread the highly transmissible delta variant and may be contributing to the ongoing spike in infections. The data helped convince officials this week to call on people to resume wearing masks indoors, regardless of their vaccination status.

Here are some significant developments:

Levine emphasized the dangers of the delta variant, saying it was at least twice as contagious as previous forms of the virus, and noted that it was the main factor behind the CDC’s decision to change its guidance on masking. She also warned that the virus would continue to mutate as more people got sick.

“Now is the time for people to get vaccinated,” she said. “That’s the best way to protect against the development of these variants.”

The pace of vaccinations has ticked up recently after bottoming out around a half million shots per day in mid-July. About 710,000 doses were administered nationwide Thursday, bringing the rolling average of daily doses to about 615,000, according to The Post’s tracking.

Addressing a major concern for parents as the school year approaches, Levine said data from clinical trials studying use of the vaccines in children under age 12 may be available by the end of the year.

“We’ll be looking at the science. It’s hard to put a date on when the scientific studies will be complete,” she said. She added that officials don’t expect “to see a different safety profile for what we saw in teens.”

A global rise in coronavirus cases driven by the fast-moving delta variant is causing shortages of critical health-care equipment in dozens of countries and threatening to upend progress against the pandemic, the head of the World Health Organization said Friday.

“Hard-won gains are in jeopardy, or are being lost,” WHO Director General Tedros Adhanom Ghebreyesus said in a morning briefing. “And health systems in many countries are being overwhelmed.”

Nearly 4 million infections were reported worldwide over the past week, up from 3.5 million the previous week, according to the WHO. Tedros warned that global infections recorded since the beginning of the pandemic were on track to top 200 million by mid-August.

“The pandemic will end when the world chooses to end it,” Tedros said. “We have all the tools we need. We can prevent this disease, we can test for it, and we can treat it.”

“And yet,” he added, “cases and deaths from covid have continued to climb.”

The increases have led to shortages of lifesaving oxygen in at least 29 countries, according to Tedros. Supplies of other basic equipment for health-care workers are also running low in many of them, the WHO chief said. He called for increased funding to pay for those needs and to boost testing, noting that testing rates in low-income countries are at 2 percent of the levels in high-income countries.

“We need more,” he said. “We need stronger surveillance. We need more strategic testing to improve the global understanding of where the virus is, where public health interventions are most needed, and to isolate cases and reduce transmission.”

In the United States, meanwhile, President Biden’s efforts to place restrictions on federal workers who haven’t had the coronavirus vaccine have sparked backlash among some state and local leaders, who are now working to oppose such policies.

Federal employees who choose not to get vaccinated must undergo regular coronavirus testing, as well as socially distance and wear masks while at work. On Friday, deputy White House press secretary Karine Jean-Pierre said federal agencies would cover the cost of regular testing of federal employees who are not vaccinated. Jean-Pierre also said the White House did not intend to return to ordering lockdowns.

“The way we see this is that we have the tools in our tool belt to fight this variant,” she said. “We are not going to head towards lockdown. … Our role again is to make sure that we get people vaccinated as quickly as possible.”

The tensions between the federal government and state officials come as health experts are sounding the alarm over the spread of the more contagious delta variant. The CDC warned in an internal document that this particularly virulent variant can cause more severe illness than others.

The document, which had not been made public, was obtained by The Washington Post.

Texas Gov. Greg Abbott (R) signed an executive order Thursday prohibiting cities and other government entities in the state from enacting vaccine requirements or mask mandates, even as new daily infections there reached 13,000 — the first time since February that Texas has reported a single-day caseload above 10,000.

The path forward relies on “personal responsibility rather than government mandates,” Abbott said. He insisted that Texans “have the individual right and responsibility to decide for themselves and their children whether they will wear masks, open their businesses, and engage in leisure activities.”

Abbott’s stance was echoed in Arizona, where Gov. Doug Ducey (R) earlier this week lambasted any enforcement of masks or vaccines. “Arizona does not allow mask mandates, vaccine mandates, vaccine passports or discrimination in schools based on who is or isn’t vaccinated,” Ducey said in a statement.

But some areas are moving the other way. In Washington, D.C., masks will again be required indoors beginning Saturday, Mayor Muriel E. Bowser (D) ordered, in a reversal of recent policy.

In Nevada, Gov. Steve Sisolak (D) has brought back the state’s mask mandate, as has Los Angeles County. New York Mayor Bill de Blasio (D) is expected to speak about any updates to requirements on Monday, according to NBC. In Virginia, Gov. Ralph Northam (D) urged all Virginians to consider wearing a mask in public indoor settings but added: “This is not a requirement, but a recommendation.”

It’s not just Democrats who are stepping up restrictions: Tulsa’s Republican mayor, G.T. Bynum, said Thursday that city employees who don’t get vaccinated may not be eligible for hazard pay, News On 6 reported.

In Florida — currently a hot spot for rising covid cases, accounting for about 1 in 5 new national cases — local mayors this week announced more stringent emergency measures. For his part, Florida Gov. Ron DeSantis (R) is maintaining his broad opposition to pandemic restrictions as tensions over mandates play out locally.

Biden said Thursday that all federal employees and on-site contractors in the United States will be required to get vaccinated or wear face masks and undergo repeated testing.

The Pentagon announced that all military and civilian personnel will be asked to attest to their vaccination status; those who are “unable or unwilling” to do so will be required to wear a mask, physically distance and comply with a regular testing requirement. Defense leaders are considering whether to add coronavirus vaccines to the full list of requirements for military personnel.

In another attempt to boost immunizations, Biden also urged state and local governments to give $100 to anyone newly vaccinated. It’s a move that mimics cash and other incentives, including alcohol and flowers, already common in places such as New York City, West Virginia and Maryland.

The Biden administration had hoped to get at least 70 percent of the public vaccinated by early July, but parts of the United States are still nowhere close to that goal. Overall, around half of the country is fully vaccinated.

Similar vaccination drives have been carried out in other countries, with varying success. Indonesia and Turkmenistan, for example, are enforcing strict vaccination mandates. In France, lawmakers approved a controversial law on Monday giving vaccinated people privileged access to restaurants, cafes and transportation beginning in August.

In the corporate world, companies in the United States are also taking a strong line. Uber, following Facebook and Google, on Thursday became the latest tech company requiring U.S. employees to provide proof of vaccination when they return to offices, with limited exceptions. Cast and crew members who work on Broadway will also be required to get the shots, with some exceptions, under an agreement announced Thursday.

Meanwhile, the polarized politics are presenting some Americans with a dilemma. In Missouri, residents are opting to take the vaccine secretly to avoid any backlash from friends and family, CNN reported. Parents and school leaders across the country are also embroiled in debates over whether millions of children should be required to wear masks when they return after the summer.