Long Covid in Vaccinated vs. Unvaccinated Populations 

For most people, mild or moderate COVID-19 lasts for about two weeks. In others, however, health problems linger even after they are no longer testing positive for the illness; the long-term effects of coronavirus can persist for months or even years (Johns Hopkins Medicine, 2022). The World Health Organization describes post-COVID-19 condition, known colloquially as “long COVID,” as symptoms that persist or return “3 months from the onset of COVID-19… last for at least 2 months and cannot be explained by an alternative diagnosis” (WHO, 2021). Such symptoms can include fatigue, cognitive dysfunction (problems with thinking and memory), and shortness of breath, among others (WHO, 2021). They may be new following initial recovery from an acute COVID-19 episode, or they may persist from the initial illness; symptoms can also fluctuate or relapse over time. While getting vaccinated for COVID-19 does lower the risk of COVID infection, research concerning long COVID in vaccinated versus unvaccinated populations is ongoing. 

A recent study published in JAMA found that “among health care workers with SARS-CoV-2 infections not requiring hospitalization, 2 or 3 doses of vaccine, compared with no vaccination, were associated with lower long COVID prevalence” (Azzolini et al., 2022). Researchers from the Humanitas Research Hospital in Milan, Italy, conducted an observational cohort study from March 2020 to April 2022 among individuals working in 9 Italian health care facilities. All health care workers underwent weekly (in COVID wards) or biweekly (in other wards) PCR tests for COVID infection and had received three doses of the Pfizer-BioNTech vaccine over the course of 2021 (Azzolini et al., 2022). Researchers defined long COVID as reporting “at least 1 SARS-CoV-2-related symptom with a duration of more than 4 weeks” (Azzolini et al., 2022). Out of 2,560 participants, 29% had COVID-19, of which 31% had long COVID. Researchers categorized participants who caught COVID-19 by whether they were vaccinated at the time of infection and then calculated rates of long COVID for each group. Notably, having received more vaccine doses was associated with lower prevalence of long COVID: 41.8% when unvaccinated, 30.0% when having received 1 dose, 17.4% with 2 doses, and 16.0% with 3 doses of the vaccine (Azzolini et al., 2022). 

Long COVID has proved quite difficult to study, in part because the array of symptoms makes it hard to define. Even determining how common it is has been challenging: while some studies have previously suggested that long COVID occurs in as many as 30% of individuals infected with the virus, other results show much lower prevalence (Yoo et al., 2022; Stephenson et al., 2021). For example, a November 2021 study of around 4.5 million people treated at US Department of Veterans Affairs Hospitals suggests that the number is “7% overall and lower than that for those who were not hospitalized” (Xie et al., 2021). To date, there have been more than 93 million COVID-19 infections in the US alone (NYT, 2022). If even a small percentage of those infections turn into long COVID, “that’s a staggeringly high number of people affected by a disease that remains mysterious” (Reardon, 2022). To that end, some researchers suggest that vaccination alone might not be the best way to reduce the risk of long-term effects of Covid. Since research on long COVID is evolving, other COVID mitigation strategies remain important to the health of individuals worldwide. 


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Reardon, S. (2022). Long COVID risk falls only slightly after vaccination, huge study shows. Nature. 

Stephenson, T., Shafran, R., & Rojas, N. (2021, August 10). Long COVID – the physical and mental health of children and non-hospitalised young people 3 months after SARS-CoV-2 infection; a national matched cohort study (The CLoCk) Study. Research Square. 

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