Reinfections lower long Covid risk but increase cumulative burden

Reinfections lower long Covid risk but increase cumulative burden

New data from Canadian health workers shows that while re-influenza is less likely to lead to long Covid, the risk increases, particularly for those who were hit hard for the first time or infected early in the pandemic.

*Important Notice: MedrxivPublish preliminary scientific reports that are not peer-reviewed and therefore not considered conclusive, guide clinical practice/health-related behaviors, or treated as established information.

Can a second bout of coronavirus disease 2019 (Covid-19) be as damaging as the first in the long run? In a study published to theMedrxivPreprint* Server, Canadian researchers found that healthcare workers in Quebec were at significantly lower risk of developing long coronavirus disease (Long Covid) after reinfections than after a first infection. However, the cumulative risk of long Covid increases with each additional infection, so the overall burden remains high.

Long Covid

Long Covid, also known as post-Covid-19 disease, is a condition characterized by symptoms that persist for at least 12 weeks after a Covid-199 infection. These symptoms range from fatigue and shortness of breath to memory problems and can have a major impact on daily life.

Over 400 million people worldwide may be living with ongoing effects of the virus. Despite the growing recognition of long Covid, many questions remain about who is most at risk and how that risk evolves with repeated infections.

A major challenge is that many symptoms overlap with other common illnesses, making it difficult to pinpoint Covid-19 as the cause. Furthermore, the lack of specific diagnostic biomarkers means that long Covid is usually identified based on symptom duration and attribution by the patient. However, as newer variants of the virus continue to spread, humans are more likely to be a new version. Therefore, understanding Long Covid's true burden, especially after repeated infections, is crucial.

The current study

This population-based study used a retrospective cohort design to examine long-term CoVID risk and severity among healthcare workers in Quebec, Canada. The research team conducted an electronic survey between May 16 and June 15, 2023, of workers such as doctors, nurses and respiratory therapists active in the province's health system during the pandemic.

The survey collected data on demographics, employment, infection history (including laboratory infections), presence and duration of symptoms, the severity of each Covid-19 episode and vaccination status. Researchers also assessed ongoing symptoms and cognitive difficulties and their impact on functional status.

Long Covid was defined as symptoms attributed to Covid-19 for at least 12 weeks (three months), and cases were classified as prevalent, resolved or indeterminate. In addition, severity was assessed based on whether symptoms were mild, moderate, or severe. Control groups consisting of participants who had never had Covid-19 and those who had recovered within 12 weeks were also included.

To assess possible participation bias, a parallel telephone survey was conducted among 7,500 randomly selected non-respondents for the online survey and 3,000 unvaccinated health workers without email access for a total of 10,500 participants invited to the telephone survey. This shorter survey included five questions about history of Covid-19 and persistent symptoms.

In addition, variant information for each infection was derived based on the timing of infection and the dominant circulating strains in Quebec. The risk of long Covid was calculated based on at least 12 weeks before the survey was completed, and comparisons were made between initial infections and reinfection.

Key Findings

The study found that Long Covid remains a prevalent and disabling condition among healthcare workers. About 17% of those who had Covid-19 reported symptoms that lasted at least 12 weeks. However, the risk of developing long Covid was approximately three times higher after a first infection compared to re-functions.

While the risk increased with each additional infection, with up to 37% of those with three infections experiencing long Covid, the likelihood of long Covid was significantly lower for each reinfection than for the original episode. The highest risk was associated with the strain of the ancestral (original) virus, with a decreasing risk seen for later variants, including Omicron. However, because Omicron was so widely used, it was responsible for almost 79% of long Covid cases.

In addition, the severity of the initial illness played an important role. People with severe acute CoVID-19 episodes, particularly those hospitalized or reporting multiple severe symptoms, are more likely to suffer long-term effects. Conversely, the risk was less than 5% for people with mild or moderate illness, be it a first infection or reinfection.

Among those who still had symptoms at the time of the survey, 43% had moderate Covid and 33% had severe long Covid, based on self-reported symptom intensity. These individuals reported a higher number of symptoms, which included high levels of fatigue, cognitive problems such as brain fog, postexertion malaise, and shortness of breath. Some cases persisted for over a year, and a small fraction lasted three years or longer. Researchers also observed seven different groups of symptoms (symptom clusters), with systemic, neurocognitive and respiratory problems being the most common in severe cases.

The survey's low response rate was a limitation as it may have overestimated long Covid prevalence, although a validation study supported the main findings. The researchers also acknowledged that reliance on self-reported data may have introduced recall bias and that the study population was predominantly middle-aged, white and female, which may affect generalizability.

High vaccination rates in the cohort (with 78.6% having received three or more doses) may have contributed to the lower risk of long Covid following Omicron infections.

Conclusions

Overall, the study confirmed that Long Covid is a persistent and serious health problem, particularly after initial infections and severe cases. While relapses represent a lower individual risk, their cumulative impact remains significant due to ongoing viral circulation.

As frontline workers continue to be exposed, it is critical to understand and address the functional consequences of Long Covid. The results emphasize that future health policies must take into account both prevention and long-term support for those affected.

*Important Notice: MedrxivPublish preliminary scientific reports that are not peer-reviewed and therefore not considered conclusive, guide clinical practice/health-related behaviors, or treated as established information.

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