In rare instances, fully vaccinated people who experience breakthrough COVID-19 infections may develop prolonged symptoms, according to a small Israel-based study published July 28 in The New England Journal of Medicine.
Researchers analyzed breakthrough infections among 1,497 fully vaccinated healthcare workers at Sheba Medical Center — the largest medical center in Israel. The study ran from Jan. 20 to April 28, when the alpha variant was the country's most dominant strain.
The study validated previous research showing breakthrough infections are rare. Just 39 workers experienced breakthrough infections, 85 percent of which involved the alpha variant first identified in the U.K. Most cases were mild or asymptomatic, though 19 percent had symptoms that lasted at least six weeks. Symptoms included a prolonged loss of smell, persistent cough, fatigue, weakness, difficulty breathing and muscle pain.
"If this is what we're going to see with all of the even mildly symptomatic infections that we're seeing now, it's definitely worrisome," study author Gili Regev-Yochay, MD, director of the infection, prevention and control unit at Sheba Medical Center, told NPR.
However, Dr. Regev-Yochay and her colleagues said further research that follows a larger number of patients for a longer time period is needed to confirm this preliminary finding. Other medical researchers agreed the topic warrants future research.
"We had hoped that when you get vaccinated and even if you did have a breakthrough infection you would have enough of an immune response that would block this protracted symptom complex now known as long COVID," Eric Topol, MD, founder and director of La Jolla, Calif.-based Scripps Research Translational Institute, told NPR. "This study is [really the] first to give us an indicator that there's some long-haulers among that small group of people that had breakthrough infections."