According to U.S. government researchers, a new nasal vaccine against influenza, which helps patients avoid the needle, has caused no unexpected side-effects.
In a study of as many as 2.5 million people who received the vaccine over the past two flu seasons, no unexpected serious risks were reported.
The nasal vaccine FluMist has had approval since 2003 for use against the seasonal flu, which kills 36,000 Americans every year and as many as 500,000 globally.
But despite efforts by U.S. health officials to promote its use, people have been reluctant to use it.
The vaccine is meant to be squirted up the nose using a special spray-like device, and is approved for healthy people aged 5 to 49.
Asthma patients however are advised to avoid the vaccine in case it worsens their symptoms.
Fears have arisen that the spray might cause unusual side effects because it must be sprayed up the nose and uses a live but weakened form of the influenza virus, as opposed to the injected shots, which use inactivated or "killed" virus.
Dr. Hector Izurieta of the Food and Drug Administration and colleagues examined the adverse events reported to the U.S. Vaccine Adverse Event Reporting System during the first two seasons of the new vaccine's use.
Izurieta says that among two and a half million people who received the vaccine, they only received approximately 460 reports of illness or problems with the vaccination, which is not a large number.
There were apparently no fatalities.
Izurieta says there were a few serious allergic reaction which were asthma attacks, among people who had a prior asthma history, and those people should not have received the vaccine.
In all there were seven reports of possible anaphylaxis, which is a severe allergic reaction; two reports of Guillain-Barre syndrome, which is a temporary inflammation of the nerves, causing pain, weakness, and some paralysis; one report of Bell palsy, a paralysis of the facial muscles; and eight reports of worsened asthma.
Apparently these side-effects were not any more common than in people getting injected vaccine, say the researchers.
As the vaccine is live, it is possible that someone could pass the virus to a susceptible person, such as a cancer or AIDS patient, and there were indeed 22 such cases reported.
However only a few of these cases were tested to see if the virus was in fact from the vaccine, or if the patient caught influenza elsewhere.
The most serious case involved a 3 year old who developed pneumonia three days after her mother was given the FluMist vaccine.
She recovered but it is unclear if the vaccine was the cause of the girl's illness.
Last year the United States lost half its anticipated flu vaccine supply when maker Chiron Corp. had contamination and lost its license.
Sanofi-pasteur and GlaxoSmithKline also make standard injected vaccines for the U.S. market.
Nearly 90 million doses are expected to be ready for the U.S. market, but of that number only 1 million will be FluMist doses.
Like the injected vaccine, FluMist provides no protection against the H5N1 avian flu, only against seasonal flu.
The report is published in the Journal of the American Medical Association.