A causal link between the AstraZeneca COVID-19 vaccine and the rare occurrence of blood clots with low platelets is "considered plausible but not confirmed," the World Health Organization (WHO) said on Wednesday.

"Specialized studies are needed to fully understand the potential relationship between vaccination and possible risk factors," the WHO's Global Advisory Committee on Vaccine Safety (GACVS) added in an interim statement. 

Earlier in the day, the European Medicines Agency (EMA) confirmed that the cases of blood clots with low blood platelets were associated with the administration of the AstraZeneca COVID-19 vaccine, but should still be listed as very rare side effects.