MC, If you are talking about "rate of thrombosis" after vaccination, when you say it is "greatly increased", you are misinformed. First, these odd and often catastrophic thrombotic events have been reported only for persons who received either of the two adenovirus-based vaccines currently in use outside of China (where the Chinese are using their own adenovirus-based vaccine). Second, there is a finite risk period following vaccination, at around 50 days. Once you are outside of that time line post-vaccination, apparently the incidence of the problem vanishes. And third, the incidence is very low, the exact estimate keeps changing but probably around 1:50-100,000 vaccinations. Severe cases are much rarer. I mentioned this earlier in this thread, but the etiology appears to involve adenovirus-specific antibodies that are cross-reactive with a certain platelet antigen. Presence of those adenovirus antibodies causes low platelets ("thrombocytopenia"). Since platelets are necessary for normal hemostasis, you would think this would cause bleeding, but it causes clot formation in fact. Now that the etiology is understood, these cases can be treated. More important, physicians now know what NOT to do in treating these patients.
For sure, high altitude poses no risk for anyone who was vaccinated with any of the four COVID vaccines. Persons with Sickle Cell anemia or with Sickle Cell trait are at risk for clotting in any situation that results in even mild hypoxemia, e.g., high altitudes.
