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Is one vaccine dose as effective as two? A local doctor gives an answer

Dr. Michael Koren said new data suggests that the first doses of the Pfizer and Moderna vaccines give a high level of protection after 10 days.

JACKSONVILLE, Fla. — Dr. Michael Koren, who heads up local vaccine trials at the Jacksonville Center for Clinical Research, said he is cautiously optimistic about the current state of COVID-19.

"I would say probably about 40 percent of Floridians are now immune to COVID-19 either by virtue of being vaccinated or by having had the illness," Koren said.

"We will hopefully get to herd immunity, some time, in my opinion, in April," he said. 

Koren is also optimistic about new data that suggests one dose of either the Pfizer or Moderna vaccines offers a good amount of protection. 

"You hardly see any infections 10 days after the first dose, even up through the time of the second dose, which would indicate at least for the short term, that one dose of Pfizer or Moderna vaccines are quite protective," he said.

"Again, that protection kicks in about seven to 10 days after receiving your first dose," Koren said. 

Why tell the public to take two doses then? Koren said just like everything else with COVID-19, there's a lot of unknowns about the virus.

"When people get together and design the research protocols, we're taking guesses. There's some things that we know, and there's some things we don't know. And for the things we don't know, we make educated guesses," Koren said. 

He said new data also shows that the second shot can have more side effects, like chills, aches and pains, than the first. Koren said if you've had COVID-19, wait 90 days until after your infection is gone before getting at least one dose. 

"Then the real controversy is that if you've had COVID, and you've had one dose of a vaccine, do you take a second dose of a vaccine," Koren said.

“I do believe that if you've had COVID, and one dose of vaccine, you may have a few more side effects, and more severe side effects from the second dose of vaccine, because now you're talking about your third exposure to the proteins from COVID-19. So, I I'm personally not requiring that for my patients," he said. 

"That's my advice, but every doctor may have a different opinion about that. And it would certainly be important to review your personal health history with a physician before making that decision," Koren said.