COVID booster shots: Whether you should get one, how long immunity lasts

Hosted by

A Thai medical worker prepares a booster dose of COVID-19 Pfizer vaccine at the Bangkok Metropolitan Administration General Hospital in Bangkok, Thailand on August 9, 2021. Photo by Vichan Poti/Pacific Press/Sipa USA.

While the FDA has yet to approve booster shots for the coronavirus, doctors across the country are getting flooded with questions about supplemental injections. 

Dr. Michael Wilkes, a professor of medicine and global health at UC Davis,  says people from all demographic groups are calling, writing, texting and coming into his office to ask for a booster. He speaks with KCRW to answer whether additional vaccine doses are necessary to provide extra protection against COVID, especially the Delta variant.

KCRW: Among the people who have already been immunized, who has diminishing immunity? 

Wilkes: “If you've had a natural infection, that immunity doesn't seem to be as strong or as long-lasting against the Delta variant. 

Vaccine immunity seems to protect us a lot longer. How long? We really don't know because the vaccines are new, and they've only been around for about a year. 

But we do know that vaccines produce an initial surge in the number of immune cells by churning out antibodies, but these do begin to drop. Still, vaccines are protecting us against severe disease, hospitalization and death.

At this very moment, the case for COVID vaccine boosters is pretty weak because they seem unnecessary for most people, and they could divert much needed doses away from people that need it much more.”

What happens to antibodies over time?

“Early reports suggest that antibody levels triggered by vaccines do fall somewhat over time — probably over six to eight months. 

But what scientists don't know is whether this drop in antibodies also results in a decline against protection for the COVID virus. This protection drop is more likely to be the case for those who are older, and those who generally respond less well to vaccinations with weaker immune systems.”

How might booster shots affect antibodies?

“You may have heard that Israel, the UK and other countries have decided to give boosters. Pfizer is, as expected, pushing hard for people to get another dose. But remember — more doses means more money for them. 

There have been a few trials to test boosters. Third doses of vaccines have been shown by Moderna and Pfizer to result in new spikes in antibodies when administered several months after the second dose. 

But I think it's still premature for us to be giving boosters to people other than the very elderly, and those who are severely immunocompromised.”

How should we think about resource allocation when it comes to boosters? 

“I think that we, as a country and a society, need to figure out: Do we want to spend this on a second booster dose? Or do we want to get more of the world immunized so that these variants decrease in their frequency?”

Do we know whether people who were vaccinated early on are getting infected now with the Delta variant at higher rates than people who were vaccinated more recently?

“A couple of weeks ago, Pfizer published data showing that the vaccine's efficacy for severe disease slipped from 96% to 84%. After six months, Moderna reported its efficacy dropped from 95% to 90%. 

We need more good unbiased data. But right now dropping immunity for otherwise healthy people doesn't appear to be a big problem.

The Johnson & Johnson vaccine seems to be less effective than the others with respect to the Delta. Should people who received that shot now be getting a different vaccine like Pfizer or Moderna?

“There is no official policy on this. As a doctor, I can't give people mixes and matches of vaccine types. It seems that mixing J&J with a dose of Pfizer or Moderna does lead to a more robust immune response. My prediction is that we will see this coming very soon.”



Chery Glaser


Darrell Satzman