Bay Area man believes he has immunity to COVID-19 after participating in Pfizer's vaccine trial

LAFAYETTE, Calif. (KGO) -- A Bay Area man volunteered for Pfizer's COVID-19 vaccine trial and now believes he could be part of the data that indicates Pfizer's vaccine may be 90% effective.

"When I left I didn't feel any different. My arm was a little bit sore."

That was in September, after Lafayette resident, Daniel Horowitz, received his first injection during Pfizer's coronavirus vaccine trial.

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"I met the criteria because I'm over 65, but I'm in good health," he said.

Horowitz also says it helped that he has some potential exposure to the virus as an attorney who meets with clients and goes to court.

The trial is double-blinded, so neither Horowitz or the researchers know whether he received the vaccine or the placebo.

Three weeks later, after his second injection at a medical facility in Walnut Creek, Horowitz said, "I got little achy in my muscles, I just don't feel right... "It went away after that day and I said, 'I think I got a real side effect.'"

So Horowitz decided to get an antibody test to check for immunity, outside of the trial, which came back positive.

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"You have a lot of antibodies and she was thrilled, so I started crying and I just said, 'then we're out of this, it's going to be over, it's going to be okay.'"

Horowitz is now confident he received the vaccine and not a placebo.

ABC7 News reporter Kate Larsen asked UCSF epidemiologist, Dr. George Rutherford, if Horowitz was making an accurate assumption.

"It's one of many explanations," said Rutherford, who is not part of the Pfizer trial.

"He could have had COVID asymptomatic SARS-CoV-2 infection as well, and been in the placebo group."

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On Monday, Pfizer said initial trial results indicate its vaccine may be 90% effective.

If the data holds, that means it would be almost as effective as the measles vaccine.

According to the CDC, two doses of MMR vaccine are about 97% effective at preventing measles; one dose is about 93% effective.

Larsen asked both Rutherford and Horowitz what they want to say to people who still don't believe in the safety of the vaccine, or are not sure they want to get it, once it is available.

Rutherford said, "I'm gonna get it the first day I can get it and I know a lot about this stuff."

Horowitz said, "all reputable scientists say that it's safe and it's been proven safe in the trials. Take a little risk, be brave, and save your neighbor down the street."

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