Blood Type and COVID-19: There May Be Something Here

Welcome to Impact Factor, your weekly dose
of commentary on a new medical study. I’m Dr. F. Perry Wilson. One of the things that has really bothered
me about COVID-19 is the dramatic variability in presentation. From asymptomatic, to sniffles, to complete
respiratory failure requiring ECMO and of course death. I’ve seen all of these first hand at this
point. And sure, we know that there are risk factors
for bad outcomes – older age, comorbidities. But ask any of us who have cared for these
patients and we’ll tell you that there is clearly other stuff going on. I’ve seen a 35 year old man with no comorbidities
fighting for his life on ECMO. It seems logical that genetics may play a
role here, but those studies are just in the early phases.

Nevertheless some tantalizing clues are emerging
– and some from really unlikely places. OK a couple of months ago, my family did tests
to figure out our blood type. We did this for no scientific or medical reason,
but because we were bored stuck at home, wanted some fun sciency stuff to do with the kids,
and found some cheap kits on Amazon. I am type O. My wife, type A.
And that was that. Until I started seeing that blood type may
be associated with the risk of coronavirus infection and death from COVID-19. This supposition immediately raised red flags
for me. Correlating blood type with various outcomes
has long straddled the border between regular science and pseudoscience – and often had
a racially-tinged flavor to them. I am pretty sure blood type does not correlte
with various personality traits, for example. So why would blood type dictate susceptibility
to a respiratory virus? But, since I am often wrong and love to find
out when I’m wrong, I looked into it.

And I honestly think there may be something
here. Caveats: data is really limited. Studies are sort of trickling out in pre-print
form and in various esoteric journals. But I’ll point out a couple that hold water
for me. The first, a pre-print out of China, looked
at just over 2000 COVID-positive individuals and reported that there was a higher infection
rate in people with Type A blood.

What you see here is that there was a higher
than expected rate of individuals with blood group A diagnosed with COVID-19 than in the
general population. Conversely, fewer than expected individuals
with blood group O appeared in the pool of those infected. Similar results were seen when the analysis
was restricted to the 206 individuals who died from COVID-19, again blood group A was
over-represented. One study, especially in pre-print form, is
never definitive, but we now have this study from New York City to add to the data. This study looked at 1,559 patients who were
tested for COVID-19 – 682 were positive. And check out the distribution of blood types
in the positive versus negative groups. Again, blood group A is over-represented and
blood-group O is under-represented among the infected. The commercial DNA testing company 23andme
has reported that their analysis of over 750,000 genomes shows a similar pattern by blood group. They haven’t published their data yet, but
you can see here that the self-reported infection rate was lower in type O indviduals and higher
in type A individuals – though overall rates are still low. This data doesn’t come totally out of the
blue. Back in the SARS era, a Hong Kong study reported
that Type A individuals were at higher risk of infection from that coronavirus.

But what’s the biologic rationale here? Even if we believe the epidemiology – the
question is “why”. There are a few theories floating around out
there, but most of them focus on antibodies. An in vitro study of the SARS coronavirus
from 2008 found that Anti-A antibodies inhibited the ability of the viral spike protein to
bind to its receptor – ACE2. So a leading theory is that people with blood
type O, like me, might be protected if they have some anti-A antibodies floating around.

Of course people with type B blood also have
anti-A antibodies, and we haven’t seen protection in them so far. The other possibility is that the antibodies
generated against the virus are cross-reactive with the blood group A antigen – so when
someone with blood group A is generating those antibodies, they might also be making antibodies
that make their platelets a bit stickier – leading to some of the thrombotic events we’ve seen
in COVID-19 patients. Of course, this doesn’t explain why the
risk of infection would be higher, only the risk of bad outcome after infection.

I’m left a bit puzzled. Am I convinced there is something here? Yes – but I’m not sure what it is. Whether it’s a direct biologic effect of
blood type, or whether blood type is a marker for something else – a nearby gene for instance
– or maybe even socioeconomic status is ongoing work. As we get more answers, we’ll tell you about
them here..

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