Philadelphia saw a renewed spike in coronavirus cases last week after social gatherings for the Thanksgiving holiday while cases were already high.

Since Monday, the city found 1,408 new cases of the virus just with PCR tests alone, and 108 cases listed as "probable" positives from rapid testing. Some cases may not be reported until later as labs are backed up with tests, delaying results.

"Why are we seeing this big increase? Well the answer is Thanksgiving. The spike in cases happened suddenly in all states of the United States at the same time," Philly Health Commissioner Dr. Thomas Farley told reporters on a Zoom call Tuesday.

The city previously warned residents not to cancel holiday gatherings and to opt for a virtual celebration instead.

After Turkey Day, case spikes were noticed in about five days, which is the typical length of time the virus needs to incubate in a host, Farley said. Contact tracers interviewed people who recently tested positive and found plenty of those cases connected to Thanksgiving gatherings.

In one case, a woman in her 20s had symptoms the day before Thanksgiving.

"She gathered with 10 family members on Thanksgiving anyway, then after Thanksgiving she went and got tested and she tested positive. Shortly thereafter, her family members started developing symptoms and at this point, at least seven others at that gathering already tested positive," Farley said.

"Stories like that happened across the city, across the state and across the nation."

Before Farley gave that cautionary tale, Mayor Jim Kenney announced he was quarantining after exposure to someone who tested positive for the coronavirus. The mayor said he has no symptoms, and will work at home while following the latest CDC recommendation to quarantine for 10 days, unless he tests negative after seven days.

A vaccine next week?

Pfizer's coronavirus vaccine trial goes before an FDA expert panel Thursday. They are expected to give a favorable review, and the FDA's leaders could give emergency authorization to the vaccine within a few days.

Farley said if Pfizer's vaccine is approved this week, "we are likely to start offering that vaccine here in Philadelphia next week."

The Moderna vaccine is also on the way and could be approved as soon as next week. In that case, Philly would be ready to distribute it the following week, Farley said.

The city has purchased ultra cold freezers to store doses. Farley noted that about 1,000 doses can fit in a space the size of a pizza box.

As NBC10 previously reported, health care workers and the elderly would have first priority in the vaccine rollout. Essential workers would be next, with a broader distribution of the doses into 2021.

President-elect Joe Biden has said he wants the coronavirus vaccine to be free to the uninsured and underinsured.

Effects of restrictions?

The city enacted restrictions in November that limited indoor gatherings, halted indoor dining, closed gyms, museums and libraries, and reduced retail capacity through Jan. 1, 2021.

"I believe these restrictions prevented the increase that we saw last week from being even worse," Farley said.

Indoor dining is still allowed, with limits, in suburban counties that haven't restricted it.

"When we put our restrictions in place, we did recommend that other areas around us put in similar restrictions. And I do think that's necessary right now," Farley said.

But it's not likely that the city would crack down further on dining or other areas right now. It's more about having that done in other places to help stop the spread, according to Farley.

"Having consistency in the restrictions across the state would be very valuable, even to us in the city," he said.

As spread is seen across all regions, it's filling up beds, especially ICU beds. But the bigger issue is staffing. When staff get sick or need to quarantine, hospitals would pull from a staffing agency to keep up with the number of patients.

In the spring, the virus was largely concentrated in the city. Now, with the spread everywhere, the urban and suburban health centers are drawing from the same pool of reserve staff, which Farley noted is stretched thin.

In the southeast region of Pennsylvania, 24% of health systems have or are expecting a staffing shortage next week, according to a state database.