Swiss and Canadian health authorities on Wednesday lifted a ban on sales of flu vaccines made by Swiss pharmaceutical giant Novartis after determining they were safe and efficient.
"The partially visible white particles are in no way external impurities, but are agglutinations of ordinary protein components of the vaccine," Switzerland's national drug agency Swissmedic said in a statement.
Novartis provided what it said was a statement from the Canadian authorities.
The Public Health Agency of Canada said in the statement it had lifted their freeze after determining they were safe, saying it was "now advising health care professionals in possession of these vaccines that they can start using them once again."
Last week, Italy first froze the sale and use of Novartis's Fluad and Begripal flu vaccines after white particles were seen in syringes carrying them, and Switzerland, Austria, Germany, France, Spain and Canada soon followed suit.
Swissmedic stressed Wednesday though that "such (particles) can in effect be created during the manufacturing of the vaccine, but dissolve if the syringe is used in conformity with instructions," pointing out that the syringe should be lightly shaken before use.
"The security and efficiency of the vaccine are in no way weakened by these (particles) present in some syringes," it said, adding that its own labs had tested the vaccines and had confirmed their quality.
Some 160,000 doses of the vaccines were affected by last week's freeze in Switzerland alone, according to Swissmedic.
Novartis said Wednesday it was "pleased" at Switzerland and Canada's decisions to resume use of its vaccines.
"We have always remained confident in the safety and efficacy of our vaccines," the company said, adding that it now was "working with the Swiss and Canadian Authorities to resume full distribution as soon as possible to protect against seasonal influenza."
"Novartis is working diligently with other health authorities to address their questions and resume distribution," it added.
Explore further: Italy, Switzerland, Austria freeze sales of Novartis flu vaccines