The roulette wheel that decides who lives and dies from the coronavirus is weighted by the type of blood coursing through the veins of victims, gifting some with innate resistance and dooming others to misery and torment.
Infectious disease specialists say the worldwide pandemic is especially cruel to people with type A blood, which apparently lacks certain compounds that help fight off the disease.
A study published June 17 in the New England Journal of Medicine found that people with type A blood have a higher risk of contracting the disease and suffering complications. The analysis, conducted by an international team of scientists, also showed that people with type O blood were at least partially protected from the virus.
It was one of several recent reports on the phenomenon, which epidemiologists say is not unique to COVID-19.
“People with Type A blood… are more likely to have severe disease and death than people with other types,” said John Swartzberg, an infectious-disease specialist at UC Berkeley. “It doesn’t surprise me because we know that blood types are associated with other infectious diseases.”
Blood type is determined by a gene that tells the body what blood cell proteins to make. The different types, A, B, AB or O, have different antigens, which determine their properties, including weaknesses and strengths. A blood type that is positive means that person’s red blood cells carry a protein called Rh, also known as the RhD antigen. Negative blood type does not.
Epidemiologists have long known that blood type plays a role in how people’s bodies react to infectious diseases, and type A — positive and negative — appears to be among the most problematic.
For example, people with type A blood have a higher chance of developing certain cancers, particularly stomach cancer. All the different types of blood have agreeable and disagreeable qualities, but type A is associated with higher levels of the stress hormone cortisol, according the National Institutes of Health.
Swartzberg said people with type A blood are also more likely to contract the most virulent form of malaria, known as plasmodium falciparum. The protozoan parasite is transmitted through the bite of a female mosquito.
On the other hand, people with type O blood are less likely to develop inflammation during infections, suffer from heart disease, pancreatic cancer or contract parasitic diseases like falciparum.
The Journal of Medicine study sequenced the genomes of 1,980 COVID-19 patients in Spain and Italy who had suffered respiratory failure and compared their results with an approximately equal number of people who were not sick. The researchers concluded that people with type A blood had as much as a 45 percent higher risk of getting severely ill from the coronavirus.
Another study, of more than 2,000 people in China last March, also found that blood group A had a significantly higher risk of coronavirus infection. That information aligns with other studies, most of them not yet peer reviewed.
In each case, type O blood was linked to lower risk and less severe illness. A study by the genomics site 23andMe calculated that people with blood type O were 9% to 18% less likely to contract COVID-19 than people with other types of blood.
Type O blood is handy in other ways. O positive is the most common blood type, and O negative is compatible with all other types of blood. Because O negative blood can be given to anybody, it is commonly used for transfusions.
Studies have shown that people with type O blood also get fewer blood clots, a serious problem among COVID-19 patients.
SARS-CoV-2, the specific coronavirus that causes COVID-19, is essentially a tiny parasite that uses its tell-tale spike proteins to latch onto the much larger human cells, like pepper on an egg. The virus uses the cell’s receptors to worm its way inside, where it replicates itself billions of times and spreads throughout the body.
There are a variety of factors that influence vulnerability to COVID-19 infection, including old age, underlying medical conditions and possibly race, although the high mortality rate among minorities is more likely related to poverty and a lack of medical care. A study, published Wednesday in Nature, said Latino and African Americans are three times more likely than white people to be infected by the coronavirus and nearly twice as likely to die.
Men are hospitalized and die from the virus more often than women, a disparity that researchers have linked to testosterone, the male sex hormone.
Researchers know that the coronavirus targets ACE2 receptors, a protein on the surface of human cells that normally helps regulate blood pressure. Peter Chin-Hong, a professor of medicine and infectious diseases at UCSF, said the genes that make the ACE2 receptors are next to the genes that provide the blood type codes.
“Because they are so close to each other they influence each other in ways we don’t understand,” Chin-Hong said. “Things are next to each other for a reason.”
Nobody knows exactly how the coronavirus operates, but some scientists believe the virus, when it infects a new host, carries with it genetic coding — blood type antigens — from its last victim. Apparently, type O blood adapts better to the coronavirus’ coding.
Swartzberg said this may have something to do with the types of carbohydrates, or sugars, on the surface of red blood cells.
“The type A carbohydrate may facilitate the entrance of the protozoan into the red blood cell, causing more severe infection,” Swartzberg said. “People with type O blood, which doesn’t have any of those carbohydrates, may be somewhat protected.”
George Rutherford, a UCSF infectious disease specialist, said caucasians of Mediterranean descent have the highest percentage of type A blood.
“Most of these (blood type) observations are from Italy and Spain, which have had horrendous COVID outbreaks,” Rutherford said.
A big puzzle is that blood type doesn’t seem to matter when it comes to African Americans and other people of color. Type O blood is more common among African Americans — a little more than half carry that type — yet African Americans have disproportionately high infection rates. The same goes for Latinos, 57 percent of whom carry type O blood.
It’s an indication, Rutherford said, that socioeconomic problems like poverty, obesity and stress may be bigger factors in who gets the disease and how ill they become than blood type.
Peter Fimrite is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: @pfimrite
