This is by far the most fascinating read I've seen so far on this thing relating to why blood types seem to matter. And, paradoxically? lays out a vaccination path way to get to herd immunity with far fewer people.
https://www.medrxiv.org/content/10.1101/2020.07.13.20152637v1
Is blood type targeting a useful vaccination strategy?
Initial preprints noting the increased risk to type A individuals have proposed that these may require additional surveillance and priority for protection. However, ABO-interference with virus transmission presents a unique and striking scenario that has not previously been modelled in detail, in which those most prone to infection are those least likely to pass it on, and vice versa. This raises the question as to whether it is more important to vaccinate the most susceptible individuals, or the most infectious individuals. Figure 3A shows (1−𝑅𝑠𝑡𝑒𝑎𝑑𝑦𝑅𝑚𝑎𝑥), i.e. the degree to which R0 is suppressed by ABO-interference, across the full spectrum of potential ABO allele frequencies for ρ212= 30%. ABO-interference suppresses transmission most efficiently when the allele frequency ratio is approximately 40% O / 30% A / 30% B alleles. Translating allele frequencies to blood group frequencies yields Figure 3B.
ABO-interference suppresses transmission most efficiently when type O individuals make up 15% of the population and type A / type B individuals are present in equal proportions. A similar shape heat map is obtained for values of ρ=20% and ρ=90% . Vaccinating type O individuals moves the population upwards in Figure 3B, while vaccinating type A or B moves the population right or left respectively. In principle, an optimal vaccination strategy will cause the distribution among susceptible individuals to move “down” the gradient, i.e. towards more effective suppression of the epidemic. Conversely, the vaccination strategy must also be careful not to disrupt the intrinsic protection afforded by ABO-interference.
To illustrate this, consider a population with 50% type A and 50% type O individuals, similar to Māori and some Polynesian populations where the type B frequency is very low. In general, the predicted herd immunity threshold is (𝑅0−1𝑅0), so in the absence of ABO-interference the threshold for an epidemic with an Rmaxof 3 is 66.7%. In such a population, if ρ= 30% then Rsteady= 2.32, the risk for type A individuals is 1.82 times higher than type O individuals, and type O individuals are 1.54 times as infectious as type A individuals.
A well-intentioned strategy to reduce infection might prioritise vaccinating type O super-spreaders before type A. However, once all type O individuals have been immunised, the protective effect of ABO-interference is abolished since the remaining susceptible population is now exclusively type A, and an infected type A individual can freely transmit to any remaining susceptible individual. Herd immunity will therefore only be attained when the full 66.7% of the population is vaccinated. The same applies in reverse if the more vulnerable type A individuals are instead prioritised for vaccination.
However, vaccinating both blood types equally produces herd immunity when 56.9% of the population is vaccinated, consistent with Rsteady in this population. This effect is further magnified if transmission is brought down by other means, for example non-pharmaceutical interventions including social distancing. For the same population and same value 238 of ρ= 30%, if Rmax= 2 then Rsteady= 1.55. In this case the herd immunity threshold is 50% of the population if preferentially vaccinating either type O or type A, but only 35.4% if vaccinating individuals at random.