To assess changes in the proportion of patients who converted to a positive anti-JC virus (JCV) antibody (Ab) serostatus before and during the COVID-19 pandemic.

Natalizumab, approved to treat relapsing MS, is associated with increased risk of progressive multifocal leukoencephalopathy, a rare opportunistic infection of the brain due to JCV. Masking and social distancing in the US during the COVID-19 pandemic profoundly attenuated the spread of seasonal influenza in 2020-2021. The mode of JCV transmission is not well defined, thus the pandemic offered a unique epidemiological opportunity to evaluate if isolation and masking during the COVID-19 pandemic affected JCV transmission.

Data from the TOUCH database for 22,375 patients treated with natalizumab in the US from 2017–2022 with available anti-JCV Ab record was assessed in annual epochs from April 1 to March 31. Anti-JCV Ab serostatus was determined by STRATIFY JCV^® DxSELECT. US regions examined (Northeast/South/Central/West) were determined using infusion site ZIP codes. 

From April 1, 2017 to March 31, 2018, anti-JCV Ab serostatus change was observed for 7.7% of patients, with serostatus change of 7.4% and 7.4% of patients in the following 2 years (2018-2019 and 2019-2020). During the first and second years of the COVID-19 pandemic (2020-2021 and 2021-2022), 7.3% and 7.2% of patients’ serostatus changed, respectively. There were no differences in serostatus change by US region. Multivariate predictors of JC seroconversion will be shown when presented.

The proportion of natalizumab patients with anti-JCV Ab serostatus change did not significantly differ during the first 2 years of the COVID-19 pandemic compared with the 3 prior years. These results suggest that, in contrast to seasonal influenza, masking and social distancing had no discernable effect on JCV serostatus changes. If not spread through social contact, further studies are needed to understand how JCV is transmitted.