(Tribune News Service) — Lots of people seem to think that if they've had COVID-19, they won't get it again. Unfortunately, scientists have lots of documented evidence that you can get it again. What's more, the second time could be even more severe than the first. Which is why vaccines are recommended even for those who've had COVID-19.

Research is ongoing into how common such infections are, and what role vaccines play is changing people's risk of a second infection.

Here are a few frequent questions about repeat infections, and what we know about them:

— How common is it to catch COVID-19 again?

According to the CDC, reinfections "have been reported but remain rare." How rare, the agency says, is a matter of ongoing research. A British study of 25,661 people from June to December 2020 found that those who had survived a case of COVID-19 had an 84% reduced risk of reinfection seven months later. Less than 2% of the study subjects who had previously tested positive for COVID-19 were reinfected. The newness of the virus, though, makes it difficult to know how long the protection lasts. Another study from October that looked at the likelihood of reinfections from other kinds of coronaviruses estimated that a person who had COVID-19 could expect to be reinfected within three months to five years, with a median of 16 months, provided they were not vaccinated.

— Why do reinfections happen?

The body's immune response to a virus is multifaceted, with antibodies, B cells, and T cells working together to fight infection. Antibodies produced by B cells act as the frontline defense against infection, and stave off reinfection initially by keeping cells from becoming infected. T cells, meanwhile, destroy cells infected by a virus.

After the threat of a virus has passed, B and T cells die off and antibody levels in the body decline. Over time, that can allow a second infection to take hold, particularly if the virus has mutated, as the coronavirus has, to something less familiar to the body.

In addition, some people don't develop a robust immune response to an initial infection to begin with, something that makes vaccination more predictable protection than natural immunity. So scientists say that if you've had the virus, you are less likely to be reinfected if you get the vaccine.

— Could the second infection be worse than the first one?

It can be. There have been cases reported of a second COVID-19 infection being worse than the first, including people who recovered at home from the first infection, but needed ventilator support in the hospital for the second.

— How do vaccinations prevent second infections?

The Centers for Disease Control and Prevention recommend that if you have already had COVID-19, you should still get vaccinated. That's in part due to uncertainty over how long natural immunity lasts and evidence that vaccines provide a more predictable immune response than natural infection.

The CDC cites a study that found unvaccinated people who had COVID-19 were still more than two times more likely than vaccinated people to be reinfected. A more recent study this year found unvaccinated people who had COVID-19 were five times more likely to be hospitalized for a second bout of COVID-related symptoms than people who had been vaccinated.

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