An association between patient blood type and severity of COVID-19 symptoms has been detected in preliminary studies.
Researchers found that patients with blood type A had a 50 percent higher chance of developing severe COVID-19 symptoms, defined as needing oxygen or to go on a ventilator.
Professor Andre Franke from the University of Kiel in Germany, one of the co-authors on the study, told the New York Times that he didn't know how blood type affects COVID-19 severity. 'That is haunting me, quite honestly' he said.
This study, which is a collaboration involving doctors from Germany, Italy, Norway and Spain, is currently undergoing peer review and has been posted to the preprint server medRxiv.
The researchers compared the genetic makeup of over 1600 patients with severe COVID-19, to that of a group of around 2200 control patients who were not infected with SARS-CoV-2, the virus which causes COVID-19. They looked for genetic variants within specific areas – loci – in the genome, and discovered two loci linked to a greater risk of respiratory failure in COVID-19 patients.
One of these locations determines the blood type of an individual, which is how the researchers discovered that Type A blood appears to be a risk factor for COVID-19 complications. The second location is on chromosome three, which has an even stronger link with severe COVID-19. This locus contains six genes, and it's not yet certain which of these influence patient response to SARS-CoV-2 infection.
The blood type locus also contains a stretch of DNA that acts as an on-off switch for a gene producing a protein that triggers a 'cytokine storm'. When the virus enters the lungs it triggers an immune response, releasing cytokines to attack the virus. However, in some patients, uncontrolled levels of cytokines are released, resulting in an overreaction of the body's immune system and an attack on the patients' internal organs. This cytokine storm can result in death.
A second preprint study, from a research group based in China, also found an association between blood type A and severe COVID-19. This study suggested that people with blood group O were less likely to catch SARS-CoV-2. The latter finding is supported by preliminary data from an ongoing study being carried out by the direct-to-consumer genetics company 23andme. The results of this study, surveying more than 750 000 23andme clients, so far indicate that people with blood type O are nine-18 percent less likely to test positive for SARS-CoV-2. These studies have yet to be peer-reviewed.
Ongoing large-scale research efforts are focused on understanding the genetics behind the varied patient responses to SARS-CoV-2 infection, including the global COVID-19 host genetics initiative, and the UK-based GenOMICC study (see BioNews 1047). It is hoped that initiatives such as these will allow better risk assessment for COVID-19 patients as well as the potential development of new treatments.