MILWAUKEE — The rollout of COVID-19 vaccines has offered a hopeful turn in the pandemic’s path. The shots help your body put up its immune defenses and fend off the coronavirus as it tries to take hold.

But those defenses aren’t perfect: It’s still possible to get a COVID-19 infection after you get vaccinated, explains Dr. Joyce Sanchez, an infectious disease specialist at the Medical College of Wisconsin.

There are a couple of factors at play here. First, the full protection from your vaccine doesn’t show up right away — it takes some time for your immune system to build up its defenses.

Your body will start kicking its immune response into gear shortly after the first shot, pumping out antibodies and raising other defenses. But the immune response probably won’t reach its peak until a week or two after your vaccination series is complete.

For the available mRNA vaccines, which require two doses, that means you could still get infected after your first dose or even soon after your second shot, Sanchez explains in an email.

“How likely that is to occur depends on many things, including the amount of precautions taken during that timeframe and how widespread COVID-19 is in your community,” she says.

Keep in mind that, even if you get infected after your shot, you did not get infected from the shot. None of the vaccines can make you sick with COVID-19, as the Centers for Disease Control and Prevention explain. 

The shots activate your immune system by making your body think it’s under attack from a virus — like by sending in little pieces of the virus, or genetic material that teaches your own cells to make spike proteins. But the injections do not send in a live coronavirus that could cause an infection. 

If you do test positive for COVID-19 between doses, Sanchez says you should still get your second shot. However, you should wait until you’re recovered and finished with your isolation period, to make sure you don’t expose anyone else to the virus.

And don’t worry too much if that means your second dose will fall outside the recommended 21- or 28-day window: Providers can schedule the second shot up to six weeks after the first, according to the Centers for Disease Control and Prevention, although you should try to keep it as close to the schedule as possible.

Another factor to remember is that even when that response is in full swing, the immune system is not offering perfect, 100% protection (although it can get pretty close).

Both the Pfizer and Moderna vaccines offer around 95% protection, which is excellent in terms of vaccines — Sanchez calls it “an extremely high-performance rate” — but still means a few infections can slip through the cracks. Other vaccines in the running for FDA authorization, including the single-dose Johnson & Johnson shot, have lower efficacy rates.

This means that some fully vaccinated people will still likely catch COVID-19. We know some already have: A handful of participants who got the shots in clinical trials still got sick. And with mutated coronavirus variants gaining traction across the world, scientists worry that the vaccines may lose some of their punch against the pandemic.

Despite these caveats, the vaccines are still a hugely important and life-saving tool, experts say. 

Immunity isn’t an all-or-nothing deal. If you do get COVID-19 after one or two shots, you’ll likely get a milder case than without the vaccine: In clinical trials, the vaccines were extra effective at preventing severe COVID-19 symptoms — the kinds that would lead to tragic outcomes. 

"Even though there is a diminished protection against the variants, there's enough protection to prevent you from getting serious disease, including hospitalization and deaths," infectious disease expert Dr. Anthony Fauci told CNN. "So, vaccination is critical."

After you get your shot, you should keep taking preventive measures to avoid exposure, the CDC recommends. 

But you can also breathe a sigh of relief. The COVID-19 vaccines aren’t perfectly foolproof — infection after a shot is possible — and yet, they’re a really effective way to protect yourself, help your community, and bring the pandemic to a close.

“We are all safer, we are all better off, and we are all closer to recovery if everybody gets vaccinated,” Gov. Tony Evers said at a Tuesday briefing.