Case series: Vaccine-induced thrombocytopenia with severe headache may precede cerebral venous sinus thrombosis by several days – patients with severe headache 5 to 20 days after adenovirus vector vaccination against Covid-19 should undergo immediate testing for thrombocytopenia and d-dimer levels and, if available, testing for anti–PF4–heparin IgG antibodies.

Vaccine-Induced Thrombocytopenia with Severe Headache – New England Journal of Medicine

Commentary on Twitter

Experience with 11 patients suggests that elements of VITT (severe headache, elevated d-dimer levels, and positivity for anti-PF4 antibodies) after ChAdOx1 nCoV-19 vaccination may precede VITT. #Covid19Vaccines #COVID19 #SARSCoV2 #IDTwitter https://t.co/mzBgjJIE6l pic.twitter.com/wGqb1gKFXk

— NEJM (@NEJM) September 15, 2021