The other thing is that I'm O blood group and everyone else is A
They are an intriguing set of studies.
Think of blood group antigens as a set of "hairs" on an cell -because that what they appear to be visually
People either have A, B, O, AB - the best analogy is people have different colour hair - black, brunette, blonde
Except that O is bald! because O is not an antigen.... more below...
One can then speculate that different types of hairs might facilitate the ability of Covid19 to attach itself to the cells. Maybe A hairs are better at helping Covid attach to cells?? Who knows what the mechanism is.
There are criticisms that the studies are not properly controlled nor have a high enough power (number needed to see an true effect).
The other part of the story is that everyone from a very young age develop antibodies to blood cells they don't have.
So O people tend to have Anti A and Anti B antibodies in their system.
Some O people don't have Anti A and Anti B antibodies and are highly sought by Blood banks because their blood can be given to almost everyone.
A people oftenhave Anti B,
B people often have anti A.
AB people have both A and B hairs and therefore don't have any anti A or anti B. And therefore they can have O,A,B blood transfusion that don’t have anti A or anti B antibodies
There is no anti-O antibody - “bald people love hair”
(of course, the Resus negative or positive (ie O negative, O positive, A neg, A pos etc etc etc) is the other important factor in blood transfusions and donations and needs to be also matched but I don't want to complicate the story)
It may be that the anti A and anti B are important in the prevention of Covid infection. People with AB don't have any anti A or Anti B antibodies. So are people with AB the most susceptible???
Speculative but as i said above intriguing.
Regardless, just assume as a human who breathes air , susceptibility is greater than zero (Fish dont get Covid cos they dont breathe air) , and I would not speculate that some people can take less precautions than others.