The social distancing measures put together to fight the novel coronavirus pandemic have had another little-known advantage: they slowed the outbreak of a viral neurological disease called acute flaccid myelitis (AFM), cases of which were expected to spike in 2020.

AFM is a neurological disease that causes muscle weakness, paralysis, and even death. The disease, which primarily affects children, is uncommon but has seen increasing outbreaks linked to a rare virus called enterovirus D-68 due to climate change-related factors.

Researchers write, “We predicted that a major EV-D68 outbreak, and hence an AFM outbreak, would have still been possible in 2020 under normal epidemiological conditions. … Our preliminary analysis indicates that the Covid19 pandemic response is likely to have affected the dynamics of a 2020 EV-D68 outbreak.” According to data, there were 153 cases of AFM in 2016. and 238 cases in 2018 — but only 31 cases in 2020. Research tracking the outbreak of the disease was published in Science Translational Medicine.

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However, the drop in cases of AFM comes with a catch. While mask-wearing and other social distancing measures prevented a 2020 AFM outbreak, researchers say it may have also caused a setback on viral immunity to the disease at a large-scale, population level, ultimately leaving more people vulnerable to infection in the future. “If social distancing prevents the outbreak from occurring, then the susceptible pool may increase even further,” the researchers write.

As of now, there is no proper treatment for AFM, and vaccine development is slow due to the rarity of the disease.