Yesterday, the CDC’s HAN (Health Alert Network) issued a detailed report regarding their recommendation to pause administration of the Janssen (J&J) vaccine (see link to this report). The CDC has now received VAERS reports from 6 women ages 18-48 of serious clotting events after the administration of 6.85 million doses of this vaccine (as of 4/12/21). These events appear to have been triggered by the development of platelet-activating antibodies against platelet factor 4 (PF4), which is also known as heparin-PF4 antibody. This may trigger Vaccine-induced Immune Thrombotic Thrombocytopenia (VITTP) which can have serious CNS consequences (1 death so far). This association is quite rare at ~ 1 case per million vaccinations. A similar problem has been seen with the AstraZeneca vaccine, which is also a viral vector vaccine (AD26), but hasn’t been seen in the USA or internationally with the Pfizer or Moderna mRNA vaccines. The key issue for the CDC and ACIP at this point, is the possible under-reporting of this association. Because these events occurred 6-13 days after vaccination, the development of this rare problem may not have been linked to the vaccine. Hopefully this HAN report will bring in more VAERS reports to allow the CDC to provide more precise information on the real risk of this event in persons receiving the Janssen vaccine. To put this preliminary risk in perspective, the known risk of “unvaccinated persons” aged 18-48 dying of SARS-CoV2 is 125/million, which is a vastly greater than the risk of acquiring (much less of dying) of VITTP.