It said it would investigate reports of clots in the cerebral veins (sinus vein thrombosis, or CSVT) occurring together with lowered platelets soon after vaccination. But the agency said use of the vaccine should continue and one official said Britain's rollout would likely not stop even if a link was proved.
The European Medicines Agency is investigating reports of 30 cases of unusual blood disorders out of 5 million recipients of the vaccine in the region.
"We have no signal of concern in this regard," Vinod Kumar Paul, who heads a government committee on vaccines, told a news conference, adding that experts in India had looked into the issue.
The suspensions have provoked intense debate over whether it was prudent to put AstraZeneca inoculations on hold just as vaccination campaigns were beginning to gather pace.
The European Medicines Agency (EMA), which is holding a special meeting on Thursday, echoed the WHO's calls for calm and said it was better to get the vaccine than not.
The EU has so far approved three vaccines -- Pfizer-BioNTech, Moderna and AstraZeneca-Oxford. Three other vaccines are under "rolling review" by the Amsterdam-based EMA -- Novavax, CureVac and Russia's Sputnik.
The European Medicines Agency said last week it would review the vaccine developed by AstraZeneca and Britain's Oxford University this month under an accelerated timeline.
Precision of procedures matters. But so does speed. The delays cost lives.
EMA said in early December it planned to decide on whether to approve the BioNTech/Pfizer vaccine by Dec 29, and another being developed by Moderna by Jan. 12.
Berlin's irritation is more acute as BioNTech is a German firm and the country is preparing to go into partial lockdown from Wednesday, with non-essential shops and schools to close.