A top vaccine investigator says there’s “not really a plausible mechanism” for AstraZeneca’s COVID-19 vaccine to cause blood clots, after 10 countries in Europe abandoned certain batches or suspended its use altogether because of the alleged risk.

Denmark, Norway and Iceland’s drug regulators suspended use of the vaccine after a 60-year-old Danish woman developed a blood clot and died shortly after vaccination.

The director-general of the Danish Health Authority said the country was “by no means discarding the AstraZeneca vaccine” and there was “strong evidence that the vaccine is both safe and efficacious”.

“However, because we vaccinate so many people, we also need to react with due diligence when we learn of possible and severe side effects.”