Receiving a COVID-19 vaccination appears to lower the risk of most categories of post-COVID conditions (PCC), according to a large study.

“Compared to unvaccinated cases, vaccinated cases had a similar or lower risk of all PCC categories except mental health disorders (RR [relative risk]: 1.06, 95% CI: 1.02-1.10),” the researchers from Kaiser Permanente Southern California in Pasadena and colleagues wrote. “Vaccination was associated with ≥10% lower risk of sensory (RR: 0.90, 0.86-0.95), circulatory (RR: 0.88, 0.83-0.94), blood and hematologic (RR: 0.79, 0.71-0.89), skin and subcutaneous (RR: 0.69, 0.66-0.72), and non-specific COVID-19 related disorders (RR: 0.53, 0.51-0.56).”

The results were published recently in Nature Communications. The study team sought to evaluate the association between prior COVID-19 vaccination and new-onset PCC, commonly known as long COVID, among patients with SARS-CoV-2 infection across eight large healthcare systems in the United States.

For the retrospective matched cohort study, electronic health records (EHR) from patients with SARS-CoV-2 positive tests during March 2021–February 2022 were reviewed. The researchers matched vaccinated and unvaccinated COVID-19 cases on location, test date, severity of acute infection, age, and sex. Vaccination status was determined using EHR and integrated data on externally administered vaccines.

For purposes of the study—which included 161,531 vaccinated COVID-19 cases and 161,531 matched unvaccinated cases—PCC was defined as a new diagnosis in one of 13 PCC categories 30 days to 6 months following a positive SARS-CoV-2 test.

“In general, associations were stronger at younger ages but mostly persisted regardless of SARS-CoV-2 variant period, receipt of ≥3 vs. 1-2 vaccine doses, or time since vaccination,” the authors explained. “Pre-infection vaccination was associated with reduced risk of several PCC outcomes and hence may decrease the long-term consequences of COVID-19.”

Background information in the articles noted that following the acute stage of illness, “a broad spectrum of sequelae of SARS-CoV-2 infection has been reported in up to one-third of recovered patients and is thought to affect more than 6% of all U.S. adults. Termed ‘post-COVID conditions (PCC)’, these include fatigue, loss of taste or smell, shortness of breath, cough, headache, pain, and a range of moderate to severe outcomes affecting the cardiovascular, pulmonary, renal, endocrine, and neurological system.”

Because of the diverse and often nonspecific clinical presentation, there have been methodological challenges when inferring causality and an exact and agreed PCC definition has not been established, the researchers pointed out.

The researchers noted that COVID-19 vaccination is known to be effective in preventing SARS-CoV-2 infection, reducing disease severity and preventing hospitalization or death related to COVID-19, but that few studies have assessed the association between COVID-19 vaccination and PCC.

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