What official claim rules apply if symptoms start after 42 days?

The 42-day rule is an administrative cutoff, not a biological one, and the evidence shows exceptions exist.

The Scottish case-crossover study that found the elevated VITT risk concentrated in days 1-14 after AstraZeneca vaccination [5] also used a 15-84 day window as the control period, meaning the study itself treated events beyond 14 days as background. The 42-day rule was set early in the pandemic before the syndrome was fully characterized. The case literature now includes patients whose symptom onset or diagnosis fell outside that window. A 2022 case report describes a patient with cerebral venous thrombosis without thrombocytopenia who presented 11 days after a second AstraZeneca dose [6] - the second dose timing means the first dose was weeks earlier. A 2021 case series of two fatal CVST cases includes one patient whose headache began 23 days after vaccination [3]. Another case report documents portal vein thrombosis from VITT after AstraZeneca vaccination, with the patient presenting with symptoms that required hospitalization [2].

The mechanism is what matters, not the calendar. VITT is an autoimmune reaction where the body makes antibodies against its own platelet factor 4 (PF4) protein, triggered by the vaccine's adenovirus vector [1, 4]. That antibody response can take time to build, and the clot itself can form slowly. The anti-PF4 antibodies can be detected by ELISA weeks after onset [1]. A positive anti-PF4 antibody test drawn during the acute phase, combined with imaging that shows the clot, is the real diagnostic test. The 42-day window is not a hard biological limit.

My call: if your symptoms started after 42 days, you should still file a claim. The evidence shows that late presentations exist, and the 42-day window is an administrative guideline, not a biological cutoff. The key is proving the mechanism with a positive anti-PF4 antibody test and imaging evidence of thrombosis. Confidence: moderate on the existence of exceptions, high on the mechanism being the real test.