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Many NFL and Major League Baseball stadiums, from New York to Los Angeles, have been Covid-19 testing sites – and now some of those same facilities are being repurposed again as Covid-19 vaccination centers.

Yet many health officials warn that balance is needed to ensure Covid-19 testing efforts continue even as the country pushes for more coronavirus vaccinations

That balance is the crux of an issue that public health officials have grown more concerned about, Dr. Marcus Plescia, chief medical officer at the Association of State and Territorial Health Officials, told CNN on Wednesday.

“Converting some of those large-scale venues from testing to vaccination, at least for the time being, makes sense – just because we do have to start to scale up the vaccination, but I think there’s a balance,” Plescia said.

“We can’t just switch everything over to vaccinations,” he said. “We need to continue to have some resources where people can get tested.”

Ballparks morph into massive vaccination sites

In Los Angeles, Dodger Stadium will transition into a Covid-19 vaccination site by the end of the week and stopped offering Covid-19 testing as of Monday, according to a statement from LA Mayor Eric Garcetti.

The announcement noted that the shift in resources “will temporarily reduce testing capacity” in LA county, but “it will more than triple the number of daily vaccines” available for locals.

“From early on in this pandemic, Dodger Stadium has been home base for our testing infrastructure, a vital part of our effort to track the spread of COVID-19, try to get ahead of outbreaks, and save lives,” Garcetti said on Monday.

“Vaccines are the surest route to defeating this virus and charting a course to recovery, so the City, County, and our entire team are putting our best resources on the field to get Angelenos vaccinated as quickly, safely, and efficiently as possible.”

In New York City, a Covid-19 vaccination mega-site will be set up at Citi Field stadium later this month, according to an announcement from Mayor Bill de Blasio. The stadium was previously used for Covid-19 testing earlier in the pandemic.

“We chose this site in part, because this was one of our testing sites. It was a very popular testing site,” Dr. Ted Long, executive director of NYC Health + Hospitals Test and Trace Corps, which will be operating the vaccination center, said during a briefing on Tuesday. “So, we’ve been successful testing there, we’re going to be successful with the vaccine there.”

Major League Baseball teams reached out to county and city health officials this week to offer every MLB stadium in the country as a mass vaccination site, Lori Tremmel Freeman, CEO of the National Association of County and City Health Officials, told CNN on Wednesday.

“These stadiums are wonderful areas to be repurposed for larger, mass vaccination efforts,” Freeman said, but she added that testing is still a priority.

“We have so many places across the country still experiencing high levels of transmission and resurgence of disease, that we can’t afford to let down the testing right now,” she said. “We’re too early in the vaccination process to do that, because we still need to mitigate and manage the spread of the disease, even while we’re vaccinating.”

Stadiums aren’t the only facilities morphing into vaccination sites or shifting focus from testing to vaccines. For instance, officials in Orange County, California announced on Monday that Disneyland Resort in Anaheim will become a vaccination site and will be operational later this week.

In Philadelphia, a nonprofit called “Philly Fighting Covid” opened a mass vaccination clinic at the Pennsylvania Convention Center last week. The group then announced on Sunday that it was “canceling testing until further notice to focus on vaccine operations.”

More mass vaccination sites are likely to pop up after the US Department of Health and Human Services announced on Tuesday that the federal government would help states set them up.

“If states wish to set up mass-vaccination sites, we stand ready to help,” US Surgeon General Dr. Jerome Adams posted to Twitter on Tuesday.

‘We’re not going to vaccinate our way out’ of the current surge

After taking a dip at the end of December, testing across the United States rebounded to the record high level it had reached before the holidays. According to the Covid Tracking Project, the seven-day average of new tests has reached more than 1.9 million per day, and has never been higher.

Covid-19 vaccinations and testing “still have to go on simultaneously” and are both “equally important” right now, Blaire Bryant, associate legislative director for health at the National Association of Counties, told CNN on Wednesday.

“Counties and local public health departments are going to find ways to continue to do testing and do testing on a mass scale,” Bryant said.

Repurposing stadiums and other large sites for vaccines will be a good thing for vaccine delivery, she said. “As far as testing goes, we know at the local public health level that that’s still very important and we wouldn’t do one to sacrifice the other.”

Testing and vaccinations serve different purposes.

From a public health perspective, “testing is necessary in the short-term to be able to react quickly when cases are increasing and prevent or interrupt outbreaks whereas vaccinations are a prophylactic solution to prevent cases and end the pandemic,” said Dr. Sadiya Khan, assistant professor of preventive medicine in epidemiology at Northwestern University Feinberg School of Medicine.

“In an ideal world we would have enough resources to optimize vaccine rollout, as well as continue testing at the volumes that are necessary,” she said. “I think there’s always going to be a little bit of give and take.”

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Plescia, of the Association of State and Territorial Health Officials, agrees that vaccination is the way out of the pandemic – but it’s not the way out of record-high case numbers and deaths the country is experiencing now.

“This issue we’re in right now with rapidly rising rates of infection, with hospitals getting filled up with more and more people dying, we’re not going to vaccinate our way out of that,” Plescia said.

“What we do now with vaccination isn’t really going to come to fruition for several months. So in order to control what’s going on now we have to continue doing the testing, doing isolation and quarantine of people, having people wear masks and maintain social distance.”

CNN’s Amanda Watts contributed to this report.