Just under two million San Diegans have been given their first dose of the COVID-19 vaccine, but it remains unclear if a third booster shot will be needed in the near future.
"The less the virus circulates, the less critical boosters are," said Shane Crotty, an infectious disease expert and professor at the La Jolla Institute for Immunology.
Crotty's research is known nationwide, and has been used by federal health officials during congressional hearings. When it comes to booster shots, Crotty said drug makers like Moderna have already been developing and testing them.
"And the booster shots did work and they also had a variant booster shot and that worked too," Crotty said.
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So, booster shots will likely be available, the question is when or if they will be needed. Crotty said it comes down to two things: how long the immunity from vaccines lasts and the unknown with variants.
"Several of these variants of concern are more worrisome than the original strain and some of them escape immunity to some degree," Crotty said. "So, essentially the variants are tougher to stop than the original virus so the vaccine might not last as long against the variants. Trying to assess those two main situations is where we are."
Crotty estimates there is a 50-50 chance booster shots will be recommended by the winter of this year, but they might not be for everyone right away.
"It's entirely plausible that there will be an in-between kind of answer — that it may be that there's a risk assessment that says, 'OK, if you’re over 65 you should get a booster immunization at this point and if you’re under 65 you can wait longer,' maybe another year or something," Crotty said. "It doesn't have to be a one-size fits all solution."
He said the best case scenario is that the vaccines last a couple of years, but we do not know that yet.
"Basically, we just need more time," Crotty said. "We just don't have a clear historical reference point for saying, 'Oh, here’s how long immunity lasts after you've had an RNA vaccine.' We’re having to measure that and watch that every month as times goes by and try and extrapolate from now until when in the future do you need the booster."
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Booster shots could also depend on local infection rates. Crotty added that for now, COVID-19 is likely to stick around in communities.
"SARS-CoV-2 is not going to be eradicated — it’s just it’s too widespread and too easily spread from person to person," he said.
Crotty says some areas will likely not get to herd immunity and continue to see pockets of outbreaks, but he said it is a key way to stop the virus, especially in internationally-traveled areas like San Diego.
"Herd immunity also isn’t just this line you suddenly cross like nothing happens before it, then everything happens after you cross it," Crotty said. "There’s a progression there and I think most people think we’re in a range where herd immunity should be having an effect now and it should get better and better the more people you can get vaccinated."
San Diego County is nearly three quarters of the way to having everyone ages 12 and over vaccinated. The state is set to fully reopen and lift nearly all COVID-19 restrictions on June 15.
