April 27, 2023 – A new study shows that people with long COVID respond differently to COVID vaccines and that the condition may be caused by a dysfunction of the immune system -- possibly explaining why some people experience symptoms for months while others recover and resume normal lives.
The study compared people who already had long COVID with people who had recovered from the virus. Both groups had not yet been vaccinated prior to the study. When researchers analyzed blood samples after people received an initial vaccine dose, they found that people with long COVID and people who had already recovered from the virus had similar immune responses at first. But after 8 weeks, the long COVID group's immune response remained elevated, while the other group’s response had declined.
The long COVID group also showed an extra immune response that tried to fight the virus in a secondary way that researchers didn’t expect. Both groups showed an initial increase in their blood of antibodies that primarily target what’s known as the “spike” protein of the coronavirus, which allows the virus to invade healthy cells. But the long COVID group also showed a prolonged increased immune response that tried to fight the part of the virus related to how it replicates.
“Theoretically, the production of these antibodies could mean that people are more protected from infection,” said researcher Catherine Le, MD, in a statement. “We also need to investigate if the elevated immune response corresponds with severity or number of long COVID-19 symptoms.”
Le is co-director of the COVID-19 Recovery Program at Cedars-Sinai Medical Center in California, where the study was conducted.
Study participants agreed in September 2020 to participate in long-term COVID research at Cedars-Sinai in Los Angeles. The new analysis was published earlier this year in BMC Infectious Diseases and included 245 people who had long COVID and 86 health care workers who had recovered from COVID but did not have long-term symptoms.
For the study, long COVID was defined as having symptoms that lasted more than 12 weeks. Common long COVID symptoms are fatigue, shortness of breath, and brain dysfunction such as confusion and forgetfulness.
The authors said it’s unclear why the two groups had different immune responses and also noted that their study was limited by a small sample size. Their research of blood samples is ongoing, with the goals of identifying a way to diagnose long COVID with a laboratory test and of better understanding what causes the condition.