But what about those who got the one-shot Johnson and Johnson vaccine?
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Experts say there are a number of possibilities.
Johnson and Johnson vaccine researcher Dr. Kenneth Kim with Ark Clinical Research in Long Beach got the shot himself in December.
Based on the latest data, this is what he tells other J&J recipients:
"Most people who get vaccinated with the Johnson & Johnson vaccine can wait a minimum of six months before they consider a booster vaccine," he said.
The latest findings show the J&J shot induced a strong neutralizing antibody response against the Delta variant and suggests immunity remains strong for at least eight months.
But Kim says, if you got the J&J vaccine and want to get an idea of your immunity, you can do this:
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"Get an antibody test and see if you still have antibodies," he said.
Kim points out a United Kingdom study indicates those who got AstraZeneca shots, which work similarly to the J&J, had a six-fold stronger antibody response when followed with a Pfizer booster.
The theory?
"You're stimulating the immune system in a different way and that is causing a more robust response," Kim said.
As for J&J recipients who are immunocompromised, the advice about boosters is still not clear. You should talk to your doctor.
Johnson & Johnson say it's working with the FDA and CDC and will share new data shortly regarding their booster shots.
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One thing Kim really wants you to know is that regardless of which vaccine you got, there is effective treatment for breakthrough infections.
If you have a pretty bad COVID infection, a new monoclonal antibody cocktail called Regen-Cove has been shown to make a significant difference.
"If you're getting progressive symptoms, come in and get treated and there's 100% prevention of death and about a 70-80% prevention of hospitalization," he said.
Also, Kim adds new CDC research shows that even if you've had COVID, your chances of surviving or avoiding another infection is much higher if you get vaccinated.