COVID-19 may increase the risk of shingles for some, Japanese study finds

Newly analyzed data from Japan adds to the evidence that COVID-19 may increase the risk of shingles.

The findings come from a case series of nearly 400,000 Japanese patients who were diagnosed with COVID-19 between January 2020 and January 2023. The investigators found that those patients had a higher incidence of shingles for a full six weeks after being infected with the SARS-CoV-2 virus. The findings were reported in the International Journal of Epidemiology.

Researchers have been investigating whether COVID-19 makes people more vulnerable to a variety of other health conditions with shingles being among the prime candidates. In October 2021, a case report suggested that the immunosuppressant Actemra (tocilizumab), which was given to a patient with severe COVID-19, might have contributed to a patient’s subsequent herpes zoster infection. Larger studies have also suggested a potential link between COVID-19 and shingles, including a Spanish study published last year that found adults had a 19% higher risk of shingles if they had had COVID-19. The increased shingles risk more than tripled if the COVID-19 case was severe.

Yet according to Jun Suzuki, M.D., Ph.D., of the Tohoku Medical and Pharmaceutical University Hospital, in Japan, and colleagues, such earlier research did not adequately account for potential confounding factors, nor did it fully address the temporal aspect of the increased risk.

To remedy those shortcomings, Suzuki and colleagues undertook a self-controlled case series (SCCS), an epidemiological method in which only individuals who have experienced a particular health event are included, and they act as their own control, the authors explained.

“One beneficial aspect of the SCCS is its automatic adjustment for all multiplicative confounders that do not vary throughout the study, effectively eliminating all time-invariant confounding factors,” they wrote.

The investigators used a database of inpatient and outpatient claims in a Japanese database to identify 399,381 patients who were diagnosed with COVID-19 over the study’s three-year period. They then identified patients who had developed shingles and received antiviral drugs in the 90 days before or after their COVID-19 diagnosis. They used those data points to calculate the incidence rate ratio (IRR) for each group.

The authors identified a total of 558 patients within their case series who were diagnosed with shingles. They found the IRR spiked for patients in the first 2 weeks after diagnosis and remained elevated during the third and fourth weeks (IRR 1.7) and the fifth and sixth weeks (IRR 1.5).

Suzuki and colleagues outlined several potential causes for the apparent elevated risk. They said lymphocytopenia resulting from COVID-19 infection could increase shingles risk by decreasing T cells. In addition, they said immunosuppressive drugs used in severe COVID-19 cases might leave patients vulnerable to shingles. They noted that the IRR for shingles was higher in patients who were hospitalized compared to those treated as outpatients, and hospitalized patients were more likely to receive immunosuppressive agents.

Finally, the investigators added the sheer physical and mental stress associated with COVID-19 may itself increase a patient's risk of COVID-19.

The authors noted that their study did not directly account for COVID-19 severity, which may have an effect on shingles risk. They said they also did not have access to data about patients’ vaccinations, and patients who were treated for shingles and COVID-19 at different hospitals may not be accounted for in the data.

Still, Suzuki and colleagues concluded that their data support the case that patients with COVID-19 are at a heightened risk of shingles. They said their findings “underscore the importance of vaccination against VZV (the varicella-zoster virus) and SARS-CoV-2 in the COVID-19 era.”