MIT Technology Review
Early evidence: In March, Chinese researchers analyzed blood types in 2,173 infected individuals and compared those results with surveys of blood types from healthy populations in the same region. They found that 38% of the covid-19 patients had type A blood, compared with just 31% of the healthy people surveyed. By contrast, type O blood seemed to lead to a reduced risk, with 26% of the infected cases versus 34% of healthy people. And type A patients accounted for a larger proportion of covid-related deaths than any other blood type. Another study at Columbia University found similar trends.
The plot thickens: None of these studies were peer reviewed. But one that was, a genome study published in the New England Journal of Medicine found that patients with type A blood had a 45% higher risk of experiencing respiratory failure after contracting covid-19, while those with type O had a 35% reduction in risk.
Reasons unknown: Scientists don’t know yet what would cause this, and there are methodological flaws to the studies that have been run so far. In any case, blood type doesn’t seem to be among any of the more significant risk factors that distinguish mild cases from severe ones. The biggest factors are still age and underlying health issues. And type O individuals are not immune to severe infection.