People who experience particular side effects after receiving a COVID-19 vaccine, such as swollen lymph nodes, may have previously been infected with the coronavirus, according to a new study published on the medRxiv preprint server. The study hasn’t yet been peer-reviewed.
Common side effects such as fever, fatigue, muscle pain and joint pain were also more common among those who had previous infections.
An earlier COVID-19 infection, but not what’s known as “long-haul COVID-19″‘ was associated with increased risk of swollen lymph nodes after receiving the vaccination, the study authors wrote.
Researchers at three hospitals in the U.K. surveyed health care workers after the first dose of the Pfizer vaccine. Among 974 health care workers surveyed, 265 reported a positive COVID-19 test or antibodies before being vaccinated.
Women and younger people were more likely to report more side effects, higher severity and a longer duration of symptoms, the authors wrote.
About 4% of those who had already recovered from COVID-19 experienced swollen lymph nodes after vaccination, as compared with less than 1% of those who didn’t have a previous infection. In addition, 8% of those who had contracted COVID-19 reported fever as a side effect, as compared with 2% of those who had never been infected.
Muscle pain and fatigue were also reported more frequently. About 30% of those who had already been infected reported muscle pain, as compared with 15% who didn’t have a previous infection. About 29% who contracted COVID-19 reported fatigue, as compared with 20% who didn’t contract the virus.
Injection site pain and gastrointestinal symptoms were about the same in both groups.
Among the 265 health care workers who had previous COVID-19 infections, 30 people reported long-haul COVID-19 symptoms that were ongoing months after being sick. Long-haul COVID-19 wasn’t associated with more severe side effects from the vaccine.
In addition, the research team didn’t find a significant difference in the number or severity of side effects based on the timeline of when people were infected and when they received the vaccine.
“There are public health implications with regards to vaccine hesitancy, which is somewhat driven by fear of [adverse effects],” the study authors wrote.
“This data can support education around vaccine-associated [adverse effects] and, through improved understanding, help to combat vaccine hesitancy,” they added.