The Swiss federal health office has requested that the spray flu vaccine developed by a Bern company be checked for side effects after 50 people reported health-related problems after using the spray.
"Nasalflu", which is called the world's first spray flu vaccine, had been clinically tested on 2,000 people before it was put on the market late last year. Despite the tests, some consumers suffered what seemed to be a variety of side effects, including partial - but reversible - facial paralysis.
"The paralysis can last from hours to weeks," said Partik Richard, spokesman for Berna, the vaccine's maker.
The Zurich institute for social and preventive medicine has been commissioned to find out if the vaccine use led to the paralysis. Results of the study are expected to be available in September.
"The first results seem to indicate the paralysis is not linked to Nasalflu," said Richard.
The spray, which is used before and during the flu season, has not been recalled. It is subject to an annual renewal of its authorisation, as are all influenza vaccines.
The vaccine, pioneered by the former Swiss Serum and Immunisation Institute, now known as Berna, was developed to provide protection from the influenza virus for up to six months.
Unlike most vaccines, this one is administered through a nasal spray, so it can be purchased from pharmacy shelf without a prescription. The company says the spray creates a protective barrier in the nose, helping to keep flu at bay.
Around 150,000 doses of the new drug were released onto the market late last year.
swissinfo with agencies