Attempts to get Americans vaccinated accelerated on Monday when the most populous state and largest city in the United States announced it would require its employees to be vaccinated against the coronavirus or have frequent testing.

All New York City urban workers, including police officers and teachers, as well as all state and local public and private health workers in California, must be vaccinated or tested at least weekly.

The Department of Veterans Affairs also became the first federal agency to order some of its employees vaccinated on Monday.

The mandates are the most dramatic response yet to the sluggish pace of vaccination across the country given the highly contagious Delta variant ripping through communities with low vaccination rates and one by federal health officials as a “pandemic of the unvaccinated.”

According to federal data, only 49 percent of people in the United States are fully vaccinated.

Misinformation and skepticism have haunted the launch of the vaccine, and in recent weeks coronavirus infections and hospital admissions have risen, with the number of new cases per day quadrupling in the past month.

Yet all three indicators are well below last winter’s devastating winter peaks, and vaccines have proven to be very effective protection against the coronavirus. Cities, private employers and other institutions are increasingly turning to mandates to ensure that more people are vaccinated.

Hospitals and health systems like New York-Presbyterian and Trinity Health have announced vaccination mandates and in some cases sparked union protests. The National Football League announced that it would punish teams with players who fail to be vaccinated. Delta Air Lines requires that new employees be vaccinated, but not current employees. And last week, a federal judge ruled that Indiana University could require vaccinations for students and staff.

New York City will require its approximately 340,000 urban workers to be vaccinated against the coronavirus or undergo weekly tests until schools reopen in mid-September, Mayor Bill de Blasio said.

The new California requirement, which will apply to approximately 246,000 state workers and many more healthcare workers, will be implemented by Aug. 23, Governor Gavin Newsom said.

At the VA, one of the largest federal employers and the largest integrated health system in the country, government officials said 115,000 frontline health workers will have to get vaccinated over the next two months. “I’m doing this because it’s the best way to protect our veterans, period,” said Denis McDonough, the veterans affairs secretary, in a telephone interview on Monday.

Eliza Shapiro, Dan Levin and Shawn Hubler contributed to the coverage.