A new preprint study from the Cleveland Clinic in Ohio has found that people who've already had COVID-19 may not necessarily benefit from vaccination.
The research indicates that out of a large pool of healthcare workers, there were nearly 0 cases of SARS-CoV-2 infection among those who had:
There was, however, a steady increase in cases among unvaccinated people who hadn't previously contracted SARS-CoV-2.
According to the researchers, the findings suggest that natural infection provides immunity similar to vaccination. Therefore, people who haven't had COVID-19 can be prioritized for vaccination.
The study is a preprint and hasn't yet been peer-reviewed for publication.
Experts say that more research is needed to determine how long immunity lasts after a case of COVID-19. Until we have that data, some infectious disease specialists are recommending that people who've had COVID-19 still get one dose.
There were 52,238 individuals included in the study. Of the 2,579 people who'd previously had COVID-19, 1,359 were unvaccinated.
The remaining 49,659 individuals hadn't previously had COVID-19, and 22,777 of them were vaccinated.
The individuals were tracked from December 2020 to May 2021, during which time none of the 2,579 people who'd already had COVID-19 (including the 1,359 who remained unvaccinated) contracted the virus.
According to the findings, vaccination significantly lowers the risk of SARS-CoV-2 infection among people who haven't already had COVID-19 - but not necessarily among people who have already had it.
Those individuals appeared to have similar immunity to those who were fully vaccinated.
Given the limited availability of the vaccines in certain countries, the findings add to the growing belief that the vaccines should be prioritized for those who haven't previously had COVID-19.
"I'd likely keep those doses for the un-immune, those who haven't had prior infection, and then go back and decide if we need to immunize [previously ill people]," Dr. Monica Gandhi, an infectious diseases specialist with the University of California San Francisco, told Healthline.
Preliminary
Evidence also consistently points to
And a study from Israel concluded that reinfection was as low in previously ill people as it was it those who'd been fully vaccinated.
"[The Cleveland Clinic study] reinforces what we are seeing clinically, which is the reinfection rate in previously infected people is extremely low and generally follows a less severe clinical course than initial COVID-19 infection," Dr. Spencer Kroll, a board certified internal medicine specialist in Marlboro, New Jersey, told Healthline.
Our immune system is robust and involves different components that work together to prevent disease.
There are antibodies, which our immune systems produce upon exposure to a pathogen. Antibody levels may wane over time but are still operative even at lower levels, according to Dr. Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security in Maryland and an infectious disease expert.
There's also the cell-mediated immune response, which involves protective B cells and T cells that appear to increase over time and remain elevated long after infection.
It's worth noting that people mount variable immune responses to infection, according to Kroll.
"Some people with documented infection do not generate antibodies," Kroll said.
Scientists are still exploring whether there are benefits to vaccinating people who've already had the infection. They're also examining how natural immunity compares to immunity from vaccination.
Adalja said that some people, who had the disease may have some immunity agains reinfection with coronavirus, which experts should consider when coming up with vaccine guidance.
"Natural immunity is not trivial and does contribute to population level immunity along with vaccinations," Adalja told Healthline.
Gandhi said that she's often asked whether previously ill people should get vaccinated. She said that the truth is, there isn't enough data, and we don't yet know how long natural immunity lasts.
Her solution: Just get the first dose. Even if it's unnecessary, that single dose can act as an immune booster.
"I'm recommending one dose after natural infection, not because of any evidence I can find," explained Gandhi, "but because of emotion."
One study found that previously sick individuals who took one dose of the vaccine had a stronger antibody response compared to people who hadn't had the infection but had received both doses of the vaccine.
Another
Adalja is also for the one-dose strategy. "A single dose of a two-dose vaccine regimen may be all that is necessary for someone with a prior infection," he said.
According to Adalja, it can be difficult to determine whether somebody has natural immunity since antibody levels decline over time, and T cells are cumbersome to measure.
The good news is that there have been no reports of dangers or risks to people who've had COVID-19 and still gotten vaccinated.
They may have more of the usual side effects - pain at the injection site and fatigue - but there's nothing dangerous in getting vaccinated after natural infection, according to Gandhi.
Ultimately, we need more research to understand the length and durability of immunity after infection.
"We also see differential effects of the infection on women, children, and elderly people, and thus we must also delineate the length and strength of immunity, as it may differ in these different groups," Kroll said.
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