The study evaluated all three vaccines, finding that no matter the booster, all study participants saw a "substantial" uptick in antibody levels after a booster shot.
Boosting also appeared safe in the short term, with people reporting the same kinds of vaccine side effects you'd expect from the primary vaccination series (headache, fatigue, sore arm, etc.)
But some residents in Philadelphia said they would hold off on mix and matching.
SEE ALSO: More boosters on the way? FDA panel to discuss extra vaccine doses of Moderna, J&J
"Better safe than sorry. You know, go with the same one," said Stephanie Joseph of Center City.
"I feel like most people will get the one they originally got. That would make sense to me," said Hajah Carpenter of North Philadelphia.
The study also found that for Johnson & Johnson vaccine recipients, antibody levels were higher if they were boosted with Moderna or Pfizer compared to if they were boosted with J&J. This could indicate stronger protection in the short term, but we also know that antibody levels fade even as other parts of your immune system come into play to protect you.
Jonathan Bierig of University City got the J&J vaccine. He says he knows what the new study may recommend, but he's not planning on deviating course from the J&J vaccine should he need a booster.
"I'd rather stay with one course and just keep it that way. If that's the case, I'll hold out for as long as possible," said Bierig.
The findings of the study will be presented Friday to the FDA's advisory committee. It's not clear if the FDA will authorize a mix-and-match strategy.
While eligible residents decide which booster shot they may be getting, the city's Friday vaccine deadline is fast approaching.
Higher education staff, students and faculty and workers in city hospitals and long-term care facilities must receive at least one dose of vaccine by Friday or have an approved exemption.
"We would really strongly recommend that they do a major push to get their staff vaccinated. What they do after the 15th --- they are not required to terminate people, they simply can't have them work," said Dr. Cheryl Bettigole, Philadelphia's acting health commissioner.