Medical professionals from Oregon Health & Science University load syringes with the Moderna COVID-19 vaccine Sunday at a drive-thru vaccination clinic in Portland, Oregon. Credit: Kristyna Wentz-Graff / AP

The U.S. is entering the second month of the biggest vaccination effort in history with a major expansion of the campaign, opening football stadiums, major league ballparks, fairgrounds and convention centers to inoculate a larger and more diverse pool of people.

After a frustratingly slow rollout involving primarily health care workers and nursing home residents, states are moving on to the next phase before the first one is complete, making shots available to such groups as senior citizens, teachers, bus drivers, police officers, firefighters and people with underlying medical conditions.

“Every shot in the arm is a step closer to ending this pandemic,” Michigan Gov. Gretchen Whitmer said.

Similarly, in Britain, where a new, more contagious variant of the virus is raging out of control and deaths are soaring, seven new large-scale vaccination sites were set to open Monday at such places as the big Excel convention center in London, a race course in Surrey and a tennis and soccer complex in Manchester.

Across the U.S., where the outbreak has entered its most lethal phase yet and the death toll has climbed to about 375,000, politicians and public health officials have complained over the past several days that too many shots were sitting unused on the shelves because of overly rigid adherence to the guidelines that put health are workers and nursing home residents at the front of the line.

As of Monday morning, about 6.7 million Americans had received their first shot of the vaccine, or just 2 percent of the U.S. population. Experts say as much as 85 percent of the population will have to be inoculated to achieve “herd immunity” and vanquish the outbreak.

Many states are responding by throwing open the line to others and ramping up the pace of vaccinations.

Arizona, with the highest COVID-19 diagnosis rate in the U.S., planned to dispense shots beginning Monday in a drive-thru, round-the-clock operation at the suburban Phoenix stadium that is home to the NFL’s Arizona Cardinals. Shots are being offered to people 75 and older, teachers and police and firefighters .

In Texas, Dallas County was scheduled to open a vaccine megasite on Monday at the spot where the Texas State Fair is held. In Houston, nearly 4,000 people were vaccinated Saturday at Minute Maid Park, the home of baseball’s Houston Astros.

Detroit is turning its TCF convention center into a vaccination center this week, with officials planning to schedule 20,000 appointments over the next month for people 75 and older. Police officers and bus drivers can also start to get vaccinated there at the end of the week, with people deemed essential workers to come after that.

“We are going to keep ramping up our vaccinations to the maximum extent the supply allows,” Detroit Mayor Mike Duggan said.

In California, one of the deadliest hot spots in the U.S., authorities were scheduled to open a drive-thru “vaccination superstation” in a parking lot near the baseball stadium where the San Diego Padres play. Health care workers will remain in their vehicles while they are given the shot, and then will be asked to stay there for 15 minutes so they can be monitored for any reactions.

California hit another gloomy milestone, recording more than 30,000 deaths overall. It took the state six months to record its first 10,000 deaths, but barely a month to go from 20,000 to 30,000. Over the weekend, the state reported a two-day record of 1,163 deaths. Hospitalizations also have exploded, and many medical centers are being pushed to the breaking point.

Florida, the longtime retirement haven with one of the biggest concentrations of elderly people in the U.S., is using Hard Rock Stadium in Miami Gardens to dispense shots, though it planned to suspend vaccinations at midday because of Monday night’s college championship football game there.

Florida followed federal recommendations in starting vaccinations first for front-line health workers and nursing home residents in mid-December.

However, instead of putting essential workers and people over 75 next in line, as those recommendations suggested, or fully completing the first group of recipients, Gov. Ron DeSantis moved to open up vaccinations more broadly to people 65 and over.

The rollouts have been uneven across the state’s counties but have been met with huge demand, with some people standing in line in the chill or camping out in cars overnight. DeSantis said public drive-thru sites will be ramped up in the coming days.

Still, there are questions of whether the rich or well-connected are getting unfair access. Florida is investigating an upscale nursing home amid reports that it administered the vaccine to wealthy donors and members of a country club along with its residents and employees.

In Massachusetts, thousands of police officers, firefighters and other first responders were scheduled to get their first dose Monday at one of about 60 sites that had been set up around the state.

Story by Lisa Marie Pane.