Reaction From Pfizer Vaccine Could Signal You Already Had COVID-19, Study Suggests

Reaction From Pfizer Vaccine Could Signal You Already Had COVID-19, Study Suggests man receives coronavirus vaccine shot A health worker administers a dose of the BioNTech/Pfizer COVID-19 vaccine at a vaccination clinic set up inside the Derby Arena at Pride Park in Derby, Derbyshire on March 31, 2021. (SCARFF/AFP via Getty Images)

By Nick Koutsobinas | Thursday, 29 April 2021 06:14 AM

A new study suggests that people who had been infected with COVID-19 prior to receiving the Pfizer vaccine may experience an adverse reaction post-vaccination.

Researchers analyzed 974 healthcare workers in the United Kingdom who received their first dose of the Pfizer-BioNTech vaccine, with study authors noting that around 265 of those recipients already had COVID-19 prior to receiving the shot.

The study identifies adverse events or AE's as "fever, fatigue, myalgia, arthralgia and lymphadenopathy" and states that those who had previously had COVID-19 were more likely to develop lymphadenopathy, or swollen lymph nodes, after the Pfizer vaccine than those who had not received it.

Roughly 4% of those who had already had COVID-19 reported this side effect after vaccination, as opposed to less than 1% of those who had not previously had the virus.

The study's authors concluded that "in a survey-based observational study, healthcare workers in the United Kingdom reported AEs experienced after their first dose of BNT162b2/Pfizer vaccine. Prior COVID-19 infection, but not Long-COVID, were associated with increased risk of self-reported AEs including lymphadenopathy post-vaccination," adding "duration since COVID-19 infection did not affect severity of AEs."

Among some of the AEs, the study suggested 8% of those who had COVID-19 experienced fever post-Pfizer-BioNTech vaccination, but only 2% who did not contract the virus previously contracted the fever post-vaccination.

The study also listed of the 974 participants, 84% were female with a mean age of 48.9. The research has not yet been peer-reviewed.