This week, US health authorities recommended pausing the rollout of the one-shot Johnson & Johnson/Janssen COVID-19 vaccine while investigations into exceptionally rare blood clots take place.

Six women suffered blood clots out of nearly seven million doses administered.

The J&J vaccine uses broadly similar vaccine technology as the AstraZeneca vaccine, known as adenoviral vectors, which has led some experts to speculate there might be a link between this vaccine platform and the very rare blood clotting condition known as “vaccine-induced immune thrombotic thrombocytopenia” (VITT).

So far, a link between adenovirus technology in general and blood clots is purely speculation — there’s no evidence yet — but it’s worthwhile for health authorities to assess the data and for researchers to try to understand: