COVID-19’s record surges along with the discovery of more contagious variants of the coronavirus make getting as many people vaccinated as soon as possible critical for ending the pandemic.

“Every time the virus multiplies in a body, there is a chance for mutation,” said Stuart Cohen, chief of the Division of Infectious Diseases and director of hospital epidemiology and infection control at UC Davis Health. “If it doesn’t have people to go into, there will be no mutations.”

Cohen spoke Thursday (Jan. 14) on a UC Davis LIVE program about COVID-19 vaccines. His hope is that enough people will get vaccinated and that we will reach a level of herd immunity relatively soon — possibly within the coming months or by the end of the year — so the coronavirus won’t be able to keep mutating.

“If enough people get vaccinated, the virus stops circulating,” Cohen said. “It’s cut off and doesn’t have people to go into, so no mutations develop.”

If it does continue to mutate, Cohen worries the virus might eventually create a variant that can evade the vaccine.

“If we slowly, slowly roll out the vaccine, that’s the perfect way to generate mutants,” he said, because vaccine-resistant variants will have a survival advantage and could multiply. “If we get people vaccinated quickly, then we have a fighting chance to stop it.”

Vaccines effective and safe

Cohen and Stephen McSorley, a professor in the School of Veterinary Medicine and director of the Center for Immunology and Infectious Diseases at UC Davis, both said that everything they know about the Pfizer-BioNTech and Moderna vaccines shows both are effective and safe.

Clinical trials showed both vaccines are about 95 percent effective, and though some people have a day or two of reactions, the vaccines are safe. But both men said they worry about some people’s hesitancy to get vaccinated, or worse, about anti-vaccination activists spreading misinformation.

“I’m old enough, I had classmates with polio,” Cohen said. “The herd immunity we have now from polio or measles or other diseases is from vaccinations, and it’s what allows people who don’t believe in vaccines to get away with it.”

McSorley said the COVID-19 vaccines have a slightly different design, but work the way all vaccines work.

“They try to fool your immune system into thinking you’ve had this infection before,” he said. “Your body has the capacity to respond to any infection. If an alien race came from outer space with a pathogen, you actually have the ability to respond to that.”

But often our immune systems need to be taught how to do that. That’s what the COVID-19 vaccines do. They teach our bodies to make more of the cells that recognize the infection, and teach them how to find it and how to combat it, McSorley said.

The COVID-19 vaccines use a system that started to be developed during the 2003 SARS outbreak. It injects us with messenger RNA, or mRNA, which is natural in our bodies. The mRNA teaches our cells to build the spike protein on the coronavirus. “Your immune system responds to that, and now it’s ready to respond to the coronavirus,” McSorley said.

Q&A highlights

• The vaccines require two doses, and both scientists urged people to get both shots on the prescribed schedule that came out of the clinical trials — which is 21 days apart for the Pfizer vaccines and 28 days for Moderna’s. “The second dose will always boost the immune response,” McSorley said.
• Are the 21-day and 28-day intervals totally fixed? Can you wait longer? “I don’t know the answer,” Cohen said. “But I do know the best way to take it is the way it’s been studied. Freelancing is not a good idea.”
• Some immunity starts 10 to 14 days after the first dose, but full immunity appears seven to 14 days after the second, according to the studies. “If you get just one shot,” Cohen said, “we don’t know how long the immune response will last or if one dose will even do anybody any good.”
• Pfizer's vaccine was shown effective in lab studies against the newest variants. Although Moderna’s vaccine has not been studied, it is likely equally effective. “The vaccines are very similar,” Cohen said. “There is no reason to think Moderna’s would be any different with the variant.”
• It’s unclear if the vaccines actually prevent us from getting infected with COVID-19 or if a vaccinated person can spread the virus. That’s why masking and social distancing are still crucial. “Many of us believe the vaccine prevents infection. That’s how other vaccines work. We just don’t have data for that yet,” Cohen said. “We do know it keeps people from getting sick.” McSorley added: “The studies were designed to keep people out of the hospital. They weren’t studying whether you can spread infection. That’s coming.”

Other advice

Among other advice from McSorley and Cohen: It’s OK to get vaccinated if you have a cold (though if you’re feeling lousy, you might want to wait). People who’ve had COVID-19 still should get vaccinated, but it’s best to wait until 90 after all symptoms are gone. Don’t worry about which vaccine you get. They are too much alike. 

“People ask whether I would choose to take the Pfizer or the Moderna vaccine,” Cohen said. “I say, ‘I’ll take the one they have. Whichever comes first.’ The only thing to know is, get vaccinated.”

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