An unusual number of severe allergic reactions to swine flu vaccinations have been recorded in Canada, where a batch of the vaccine from GlaxoSmithKline has been recalled, the WHO said on Tuesday.
"An unusual number of severe allergies to the vaccine have been detected in Canada," World Health Organization spokesman Thomas Abraham told AFP.
"The Canadian authorities are conducting the appropriate investigations on the vaccines" and "recalled a batch of vaccine from GSK."
"We need to understand what happened in Canada," he added.
Abraham said, however, that the WHO had not changed its recommendations regarding swine flu vaccines.
Last week, the WHO said checks on many of the 30 deaths recorded following mass pandemic flu vaccinations had so far ruled out a direct link to the vaccines.
The fatalities made up a minute fraction of at least 65 million doses of swine flu vaccines which have been administered, said the WHO, citing data from 16 countries.
For every 10,000 doses of vaccines administered, only one report of adverse effect had been logged.
Of every 100 reports of adverse effects, five are serious cases such as death, according to the WHO.