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Experts say immunity from a past infection may not be enough to keep people from becoming sick again with COVID-19. Houston Cofield/Bloomberg via Getty Images
  • Researchers say people who’ve had COVID-19 but remain unvaccinated are more likely to develop the disease again than those who’ve been vaccinated.
  • They note that people who developed COVID-19 last year probably didn’t have the Delta variant.
  • They add that there’s a possibility that people who’ve had COVID-19 may need only one dose of vaccine, although that issue needs more study.

People who have recovered from COVID-19 and are leaning on their post-illness immunity rather than opting for a vaccine might want to take note.

A new report from the U.S. Centers for the Disease Control and Prevention (CDC) states that those who do not get vaccinated after the illness are nearly two and half times more likely to develop COVID-19 again.

The latest research reaches the opposite conclusion of a pre-print study the Cleveland Clinic released in July.

While the new study isn’t surprising news to infectious disease experts, they say this study, based in Kentucky, backs up what they suspected to be true.

“All the dots were there, but we had not explicitly connected those dots,” Dr. Gregg Miller, chief medical officer at Vituity as well as a front-line emergency medicine physician at the Swedish Edmonds Campus in Seattle, told Healthline.

This CDC study, he said, does just that.

“The evidence is very clear,” Miller said. “If you’ve had COVID-19, you should still get the vaccine.”

Researchers said their study revealed that in Kentucky residents who had COVID-19 in late 2020, those who remained unvaccinated were 2.34 times more likely to contract the virus again than those who were fully vaccinated.

While the report supports the notion that an infection offers some immunological boost for about 90 days, it points to a higher symptomatic disease rate among the unvaccinated.

In addition, said Miller, those initial cases came before the Delta variant had officially come on the scene in the United States.

“This is really critical (information),” said Alyson Cavanaugh, DPT, MPH, PhD, an author of the study who serves as a CDC epidemic intelligence service officer.

“Physicians and all healthcare providers are asked about this all the time,” Cavanaugh told Healthline. “They want – and now have – the science behind it.”

Experts hope the findings persuade those who’ve had the disease to get vaccinated.

“That this was done pre-Delta makes this even more compelling,” Miller noted. “If you had COVID-19 (in late 2020), chances are you had the Wuhan or the Alpha. With Delta out there – a stronger virus – we all need to pay attention to this information. I do think this will help [boost vaccine rates among the previously infected].”

Joan Parker of Tennessee had COVID-19 last fall.

Nevertheless, the findings from the CDC report aren’t changing her plans to get vaccinated.

“I’ve decided until my job requires it or it directly impacts travel (somewhere I’d like to go), I’m not getting the vaccine yet,” Parker told Healthline. “Never saying never. Just not right now.”

Kris Fletcher of Indiana told Healthline the report makes sense to her as a person who had COVID-19 and decided to get vaccinated afterward.

“Having COVID-19 was horrible, and we know it could’ve been so much worse for us (and our daughter),” she said. “In our opinion, having COVID-19 isn’t enough protection against other variants.”

Fletcher added that she and her family want to lessen symptoms should they develop the disease again.

Miller hopes this report gets more people to make the same decision Fletcher did.

One place he feels this might have an immediate uptick is within the healthcare community.

Many healthcare workers, he said, were hesitant to get the vaccine after having COVID-19 for what he sees as “very reasonable reasons.”

Now, he said, he hopes this newly gathered information “helps sway them” toward vaccinating.

“Now they can look at this study and say, ‘OK,’” he said.

Among those resisting the call to get vaccinated is Kylee Robinson of Virginia, who had COVID-19 but is still holding off on vaccination.

Robinson wants more information, such as mortality rates and the level of sickness from those who developed the disease again, issues the study did not address.

“I’d be more interested to find out what our mortality rate is before (this report) affected my thought process,” Robinson told Healthline.

Cavanaugh said the CDC would continue to monitor reinfections and continue researching.

But for now, she said, this study clearly shows vaccinating after the disease decreases the risk of developing the disease again.

Miller said people who question any danger to the vaccine being administered after having the disease can rest easy.

He said that in the clinical trials leading up to the emergency use approval, Moderna had more than 500 people in their studies who had previously developed COVID-19. Pfizer had more than 1,000 such participants.

“There was no difference in side effects for those who had contracted COVID-19 prior (to those who had not),” he said.

As more is learned, Miller asks whether people who’ve had COVID-19 might be able to get only one of the two-shot series.

That’s supposition, he said, but something that should be studied as well.

One thing is clear, he said: Those who remain unvaccinated after having had the disease remain at a higher risk.

He hopes that message gets through.

So does Cavanaugh.

“The important takeaway is simple,” she said. “Among those who’ve already had COVID-19, reinfection is nearly two and a half times higher when not vaccinated.”

“As an epidemiologist, this is really critical,” she added.