It seems like we only just got vaccinated, and it’s already time to talk about COVID booster shots. The federal government has already announced a plan to begin giving additional doses starting this fall, based on data and studies from both Moderna and Pfizer-BioNTech. But given that many folks have only just gotten a handle on the first round of vaccines, it’s understandable that there are still many lingering questions.

Do I need a booster?

Yes and no. All of the current shots, including the Johnson & Johnson option, provide strong protection against severe disease and death from COVID, even many months after initial injection (or injections). Even this fall, experts expect that anyone who is fully immunized (that’s two shots of either mRNA vaccine or one of the J&J) will still be protected against these outcomes.

But the recommendation to get a booster isn’t because the current vaccination protocol isn’t effective. It’s because even the best vaccines will wane in efficacy over time. Pfizer-BioNTech data, for instance, show that their vaccine’s efficacy against symptomatic COVID dropped by about six percent every two months (at least through the six-month study period), but still prevented 97 percent of severe disease. The company also found that giving a third dose five to eight months later resulted in significantly higher antibody levels than just two doses. Johnson & Johnson has provided similar results for booster shots for their single-dose option, with a second dose six months after the first: They see a significant uptick in antibody levels following a booster. It’s unclear yet how much extra protection these supplemental shots might provide, since the actual efficacy of the additional jabs hasn’t been evaluated.

This is all to say that if you’re fully vaccinated, you’re highly protected against getting a serious case of COVID-19, but, even so, it’s likely a good idea to get a booster shot later. Given how rapidly the coronavirus is still spreading, extra protection isn’t going to hurt. And if you’re immunocompromised in some way, public health experts strongly recommend getting an additional dose, given that impaired immune systems have a harder time mounting a proper response to vaccines.

When should I get a booster shot?

Currently the Centers for Disease Control & Prevention (CDC) are recommending that folks who got either the Pfizer-BioNTech or Moderna shots get a booster eight months after their second dose.

Should I get a booster if I got the J&J vaccine?

The CDC is still waiting on data from Johnson & Johnson to show whether a booster will be necessary and advantageous, but it’s expected that a plan will roll out as soon as that information comes in. It’s unclear yet whether the timeline would be the same eight months, but since the J&J shot didn’t get an Emergency Use Authorization until the end of February, there’s still time for the CDC to evaluate data before making a decision.

How protective are boosters?

It’s not yet certain just how much protection a booster shot might provide, in terms of preventing everything from infection to severe disease or death. Since the mRNA vaccines still offer very strong protection against the most serious outcomes, efficacy on those fronts isn’t likely to increase much. The main target would be to increase protection against symptomatic cases, or potentially decrease the likelihood of harboring an infection in the first place. Curbing these less severe cases is still crucial, in part because it helps to slow the overall spread. The longer it takes your body to clear the virus (and the more you’re sneezing or coughing), the more chance you have of spreading the coronavirus to others.

There’s also ongoing discussion about whether mixing and matching vaccines might offer additional protection. If you got an mRNA vaccine, for instance, opting for the J&J shot might round out your immunization wheelhouse, so to speak—and vice versa. The idea is essentially that, because the vaccines work differently, getting multiple types of jabs could broaden your immune response. Adenovirus vaccines like J&J or Oxford-AstraZeneca, tend to produce high levels of T-cells (one type of immune cell), whereas the mRNA options like Pfizer-BioNTech and Moderna are better at prompting an antibody response.

There have been a few studies done in the UK and EU that suggest this might bear out in the real world, though so far they’ve all only looked at immune responses, not efficacy at preventing disease. But it does seem that, especially for folks who got a single shot vaccine, changing up the type could help.

[Related: Should we be mixing COVID-19 vaccines for better immunity?]

Will I need more than one booster?

There’s been some speculation, mainly by the CEOs of the pharmaceutical companies, that the COVID vaccine will become much like the flu shot or perhaps the tetanus vaccine, which you’re recommended to get every one or 10 years, respectively. But it’s uncertain at this point where the coronavirus vaccines might fall on that spectrum, in part because it depends on a lot of factors: How much do the vaccines wane in efficacy? How widely is the coronavirus circulating, and how quickly is it mutating? How many people have gotten the vaccine? All of these issues and more will influence whether we end up needing additional jabs or not.