If you spend much time on social media, you’ve probably seen posts with questionable information about COVID-19 vaccines.

A member of Congress recently compared vaccine requirements to expecting everyone to take a Tylenol in order to make her headache better, implying that if you protect yourself, other people’s decisions are irrelevant. Others have taken spun news about “breakthrough” infections among vaccinated people as evidence that no one should bother getting the shot.

Reality is a little more complicated, and it doesn’t make a very good meme.

The Denver Post compiled answers to questions about vaccines, breakthrough infections and what it all means for you.

I’ve read that the vaccines’ effectiveness has fallen. Should I be worried?

Short answer: not really, unless you’re at high risk for severe illness, in which case you might consider getting a booster.

A study released by the Centers for Disease Control and Prevention found that while the Moderna vaccine continued to reduce the odds of severe disease by more than 90% four months after the second shot, the Pfizer vaccine fell from 91% effectiveness to 77%. There wasn’t enough data to tell if anything changed for the Johnson & Johnson vaccine, which was 71% effective at the beginning.

Keep in mind, that’s still well above the 50% efficacy that the U.S. Food and Drug Administration said it would consider sufficient for authorizing a vaccine last year, and better than the seasonal flu vaccine, said Dr. Lisa Miller, associate dean at Colorado School of Public Health.

“It does really, really well” at preventing severe disease, she said.

Some people, understandably, take a 77% effectiveness rate to mean that if they got the Pfizer vaccine, they now have a 23% chance of ending up in the hospital. But that’s not what those numbers mean.

What they’re saying is that in a typical group of 100 people with COVID-19, about 77 of them are going to be unvaccinated and 23 will be breakthrough cases. Breakthroughs tend to cause less severe illness, though, so the odds that those 23 will recover without needing intensive care are significantly better.

If vaccinated people can still get the virus, why should I bother?

The vast majority of breakthrough infections don’t cause serious illness. An outbreak during summer festivities in Provincetown, Mass., infected more than 1,000 people, including more than 700 who were vaccinated — but only seven people were hospitalized, and no one has died.

In the first week of September, Colorado had roughly 17 hospitalizations for every 100,000 unvaccinated people, and about three hospitalizations for every 100,000 vaccinated people, meaning the odds of serious illness were about five times lower if you’re vaccinated. The odds of testing positive, with symptoms or without, were about three times lower.

That said, your individual risk of a more severe breakthrough infection is higher if you’re over 65 or have a chronic condition, especially one that affects your immune system. That’s why the CDC recommended those groups consider getting a booster shot, if they’re six months out from their second Pfizer shot.