Why you're feeling stronger reactions from second dose of COVID-19 vaccine

FRESNO, Calif. (KFSN) -- All vaccines may cause some degree of reaction, and the same goes for COVID-19 vaccines.

"That first one introduces it, gets you the idea of making some of the spike proteins, gets that initial response going, but your second one is really basically ramping up numbers," said Dr. Kenny Banh of UCSF Fresno.

"That's normal to have after that second one, or a stronger response. It's preparing its weapons of war so that if it ever sees COVID, it's got it ready."

The mild symptoms are a sign that your body is building protection against the virus strains and should go away in a few days.

"We've given out 16,000 vaccines here on site, and I have seen one moderate reaction in 16,000 vaccines," he said.

According to Dr. Banh, younger people experience more symptoms than people who are older.

"A lot of it is immunologic or inflammatory response to it. So, older people don't respond as well. That's why we looked at second dosing because their response to the first dose is not as strong as we'd like."

While there are studies on mRNA vaccines that show antibodies protect against COVID-19 for eight months, he believes it's much longer than that.

"My prediction is it probably will have efficacy for more than a year for two to three years, but understand that every year you just sort of slowly drop down. it's not perfect. you're 90 percent, then you're 70 percent in year two, then you're 50 percent in year three."

You might expect that getting infected with COVID would give you that same eight months of protection, but Dr. Banh said it is a lot shorter.

The antibodies last at least three months. Although uncommon, after those three months, it's possible to become infected again.

"We do recommend anyone who has a COVID infection do get vaccinated as well," said Dr. Banh.