So, patients developing a new-onset headache, around a week after vaccination with an adenovirus vector-based vaccine, with or without other neurological symptoms should be carefully followed up for the risk of developing cerebral venous thrombosis: risk factors also include thrombocytopenia, anti-platelet factor 4 antibodies, and multiple organ thrombosis, i.e. vaccine-induced immune thrombotic thrombocytopenia. This evidence concerns the gene PF4 and Thrombocytopenia.