MG Heightens Severe COVID-19 Risk, but Vaccination Helps Reduce Risk

People with myasthenia gravis (MG) had a higher risk of hospitalization for COVID-19 compared to the general population and a control group of people with rheumatoid arthritis (RA).

People with myasthenia gravis (MG) have a higher risk of hospitalization if they contract COVID-19 but they appear to benefit from vaccination in similar ways to the general population, according to a new study.

The report, which was published in JAMA Network Open, is believed to be the largest study of its kind since the start of the COVID-19 era.

Corresponding author Carolina Barnett, MD, PhD, of Toronto General Hospital, wrote that people with chronic diseases like MG are believed to be at greater risk of severe COVID-19 due to their immunosuppressed state. However, there has been relatively little research on how the infection affects people with MG, they said.

In the new study, Barnett and authors utilized an administrative database from Ontario, Canada, to identify patients with MG, along with matched controls from the general population, and a second cohort of controls made up of individuals with rheumatoid arthritis (RA).

“Because our administrative data are limited regarding medications, we also matched to a cohort of individuals with rheumatoid arthritis (RA) to account for a potential association of immunosuppressive treatments with COVID-19 outcomes,” they explained.

Out of a total pool of more than 11 million people, they found 4411 people with MG, and matched them to 22,055 people in the general population and 22,055 people with RA. All 3 cohorts had a mean age of 66.7 years, and all had a slight majority of women. Nearly 9 in 10 residents of each cohort lived in urban areas.

Between January 15, 2020 and May 17, 2021, the investigators found 164 people with MG (3.7%) had a positive polymerase chain reaction COVID-19 test. That compared to 669 people in the general population cohort and 668 people in the RA cohort (3.0% of both cohorts).

However, once infected, the data confirmed that people with MG were at higher risk of severe disease. More than one-third of people with MG who got COVID-19 ended up in the emergency department (36.6%), compared to 24.4% in the general population and 29.9% in the RA cohort.

Hospital admissions were also more common in the MG group (30.5%) than in the general population cohort (15.1%) or the RA cohort (20.7%). Finally, 30-day mortality was higher for people with MG (14.6%) than for people in the general population (8.5%) or those with RA (9.9%).

Barnett and colleagues noted that one reason for the higher rates of severe disease compared to the general population could be the higher prevalence of comorbidities in the MG group. “However, patients with MG were also at higher risk of severe COVID-19 outcomes compared with controls with RA, where comorbidities were well balanced and where immunosuppression is also common, suggesting that there may be factors specific to MG associated with these worse outcomes,” they wrote.

The good news, Barnett and colleagues said, is that vaccines appear to significantly reduce the risk of hospitalization. Among people with MG, 80.3% had received 2 vaccine doses by August 2021, and another 3.1% had received one dose. The general-population cohort had similar vaccination rates.

The investigators found that patients with MG who were vaccinated had a lower risk of contracting COVID-19 compared to those who were unvaccinated (HR, 0.43; 95% CI, 0.30-0.60). In fact, they said the benefit of vaccination appeared to be somewhat higher in the MG group than in the controls (HR 0.70; 95% CI, 0.57-0.84).

Though some fear the vaccine may lead to flare-ups of MG, Barnett and colleagues said they found only a “negligible” number of hospital admissions within 30 days of vaccination, “suggesting that the vaccine is safe from an MG perspective.”

Altogether, the investigators said their data show that MG confers a higher risk of severe COVID-19 on patients, but also that such risk can be mitigated through vaccination.

“Our results support the prioritization of people with MG for vaccination as well as for consideration of early therapeutics for COVID-19, such as antivirals and/or monoclonal antibodies,” they concluded.


Alcantara M, Koh M, Park A, et al. Outcomes in COVID-19 infection and vaccination among individuals with myasthenia gravis. JAMA Netw Open. 2023;6(4):e239834. doi:10.1001/jamanetworkopen.2023.9834

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