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Experts say that's because it takes time for the antibodies to develop in your body.
"I have no problem putting needles in people as a doctor, I do not particularly enjoy having needles put in me," said Dr. Amy Herold, chief medical officer at Queen of the Valley Medical Center in Napa, California.
She took the coronavirus vaccine just like thousands of others.
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In regards to what happened to the nurse in San Diego, "My guess is that they were exposed just before they got the vaccine, and they weren't showing symptoms yet or just afterwards," Herold said.
"It's a sad coincidence that if somebody has already been exposed and gotten vaccinated, the vaccine doesn't work within days. I mean it does work within days but certainly not in less than a week," said Dr. Yvonne Maldonado of Stanford.
Doctors told our sister station KGO-TV that the first vaccine shot gives 50% immunity, which doesn't kick in for a week with the Pfizer vaccine and two weeks with the Moderna vaccine. The second dose then brings immunity to at least 90%.
While neither one is at 100%, Herold said there is optimism in her hospital, and she couldn't help but smile when she got the vaccine.
"Under my mask, I have the biggest grin that I'm finally getting it because it feels like hope right now and for all of us that are taking care of COVID patients and kind of stretched to the limit right now," she said. "To have something to look forward to and hope for is a very powerful thing."