Fully vaccinated people half as likely to develop long-term COVID-19, study suggests

Woman details an array of symptoms she's dealt with nearly 1 year after contracting COVID-19

March 15 will mark one year since Amy Watson, a preschool teacher from Oregon, first began suffering with COVID-19 symptoms, and she still has a fever. "Today is 353," said Watson on March 3.

A study of breakthrough COVID-19 infections published this month suggests that fully vaccinated people are half as likely to develop long-term COVID-19 symptoms.

While most people with COVID-19 recover within weeks of illness, some experience ongoing health problems for weeks or months after first being infected with the virus in what’s become known as "long-COVID" or "long-haul COVID." The U.S. Centers for Disease Control and Prevention says the conditions can range from brain fog, fatigue and persistent loss of taste or smell, to a "pins-and-needles feeling" and even the development of autoimmune conditions.

The CDC and experts around the world have been working to better understand why COVID-19 infection can impact some people long-term — and who is most at risk.

The new findings, published Sept. 1 in the journal The Lancet Infectious Diseases, included self-reported data from adults in the United Kingdom between Dec. 8, 2020, and July 4, 2021. The breakthrough cases — or reports of when a vaccinated person becomes infected with the coronavirus — were analyzed by researchers from both U.K. and U.S. institutions.

"We found that the odds of having symptoms for 28 days or more after post-vaccination infection were approximately halved by having two vaccine doses," researchers wrote in the study. "This result suggests that the risk of long COVID is reduced in individuals who have received double vaccination when additionally considering the already documented reduced risk of infection overall."

TOPSHOT - An attending physician listens to the breathing of a patient who is recovering after admission to an intensive care unit (ICU) in the coronavirus (COVID-19) patient nursing department of The HMC Westeinde Hospital in The Hague on April 4, 2

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The researchers analyzed data from more than 1.2 million adults who shared any symptoms on a mobile app called the COVID Symptom Study. It included reports from those who had received vaccines developed by Pfizer-BioNTech, Moderna or AstraZeneca — and compared findings to a control group of unvaccinated people.

Out of the 1,240,009 participants in the study who reported receiving the first dose, 0.5% — or 6,030 — tested positive for breakthrough COVID-19 infections. Among the 971,504 people who reported receiving a second dose of the vaccine, just 0.2% — or 2,370 — later tested positive for COVID-19.

Some groups were more vulnerable to a breakthrough virus infection than others, according to the study. The odds after the first dose of a COVID-19 vaccine were higher in "frail, older adults and in those living in more deprived areas," and as well as for obese individuals.

In addition to being less likely to develop long-COVID, fully vaccinated individuals were also less likely to have more than five symptoms in the first week of illness and less likely to be hospitalized, compared to unvaccinated people, the researchers said.

Overall, COVID-19 symptoms were more common in the unvaccinated participants across age groups.

"Fully vaccinated individuals with COVID-19, especially if they were 60 years or older, were more likely to be completely asymptomatic than were unvaccinated controls," the researchers wrote. "This finding might support caution around relaxing physical distancing and other personal protective measures in the post-vaccination era, particularly around frail older adults and individuals living in more deprived areas, even if these individuals are vaccinated."

The U.S. has faced a surge in COVID-19 infections this summer, fueled by the highly contagious delta variant. The CDC says the current vaccines remain highly effective at preventing severe disease and death, including against the delta strain.

But the agency in late July recommended fully vaccinated people once again wear masks indoors, citing new data showing the delta variant is more infectious and can lead to increased transmissibility when compared with other variants, even in some vaccinated individuals.

In addition to the now-dominant delta variant, experts say breakthrough infections may also be a combination of waning immunity from those who were vaccinated eight months ago and fewer community mitigation measures to stop the spread.

U.S. health officials have announced plans to administer COVID-19 booster shots to all Americans to shore up their protection, pending U.S. Food and Drug Administration and CDC approval.

While there is still much to learn about the rapidly evolving virus and long-term COVID-19 conditions, the CDC says the best way to prevent infection is by getting vaccinated as soon as possible.

"Rapid and multi-year studies are underway to further investigate post-COVID conditions. These studies will help us better understand post-COVID conditions and how to treat patients with these longer-term effects," the agency states on its website.

"To maximize protection from the Delta variant and prevent possibly spreading it to others, get vaccinated as soon as you can and wear a mask indoors in public if you are in an area of substantial or high transmission," it adds.

This story was reported from Cincinnati.