Now that over 40% of San Franciscans have received at least one dose of a COVID-19 vaccine, some of the city's most popular parks were inundated with warm bodies Saturday — sparking mild concern from some local medical experts.

San Francisco has been a national model in handling the pandemic ever since the city, along with five other Bay Area counties, enacted its historic shelter-in-place order on March 17 of last year. Had the rest of the nation followed suit in our handling of the pandemic, some 364,000 more Americans could well be alive today "if the U.S. mirrored SF’s Covid mortality rate," according to Dr. Bob Wachter, chairman of the UCSF Department of Medicine.

All things considered: This weekend's clear skies and springtime weather lead to city parks, like Mission Dolores, becoming inundated with denizens of the city. While mask-wearing was still entirely on display at SF beaches and green spaces Saturday, relaxed social distancing practices were also visible — surprising epidemiologist Jessica Malty-Rivera.

"It's not the point yet where we should be having large, unmasked gatherings, even in public settings," she said to NBC Bay Area. "There was just no physical distancing I could see insight." (This tweet basically proves just that.)

As the news outlet noted, social distancing circles were once painted atop the grass at Mission Dolores Park, giving people a visual representation of what proper space is needed between other park goers. Alas, those are no longer there.

However, Malty-Rivera did note that many people out yesterday wore and kept their masks on.

This weekend's crowds come after Bay Area medical experts warned that the pandemic’s end isn't anywhere yet in the – and now's not the time to let our guards down. Especially if we're still in the "honeymoon" phase of our region’s recovery.

“I think, certainly in California, there’s a very good chance that we’re going to have a brief honeymoon, and then it will get worse again,” said Dr. Stefano Bertozzi, a professor of health policy and management and dean emeritus of the UC Berkeley School of Public Health, to the SF Examiner. “I’m worried as we increase vaccination that we will be applying selective pressure to the virus to develop vaccine-escape mutants, and so there is a future in which this goes on for much longer than we hope."

Bertozzi's concerns were also echoed by Dr. George Rutherford, an epidemiology and biostatistics professor and the director of UCSF’s Prevention and Public Health Group.

“We’re getting there,” Rutherford said to the newspaper in regards to herd immunity.

Rutherford previously mentioned that even though some 40 percent of the state’s population has some semblance of immunity, there's going to be a cost to pay if we become too relaxed with social distancing measures — especially as emerging new strains continue to find footing in the Bay Area.

“The variants are of concern and ongoing transmission is of concern and the more that there’s ongoing transmission around the country, the more there’s going to be pressure here," he added. "I think we’re maybe at the 25-yard line."

Yes, there's reason to wax in our collective optimism, but it's no reason to let up the very practices that helped bend the curve to get to this place. And with virtually all Calfirnian's becoming available to relieve a COVID-19 vaccine in less than three weeks, here's hoping we'll at least be at the 50-yard line by the end of April.

Related: San Francisco, Marin, and Santa Clara Counties Move to 'Orange' Tier Allowing Gyms, Restaurants, and Bars to More Fully Reopen

All Three Major COVID Variants Now Present In Bay Area As Santa Clara County Confirms First 'P.1' Case

Two Bay Area Counties Have Expanded Vaccine Eligibility to 50+ Set

Image: In an aerial view by drone, new social distancing circles are shown at Dolores Park on May 20, 2020 in San Francisco, California. The move follows similar efforts by other parks in cities around the world in an effort to get back to some semblance of normalcy. (Photo by Justin Sullivan/Getty Images)