A senior executive with the pharmaceutical giant Novartis says the company is working around the clock to provide countries with the information they need to release flu vaccines currently being withheld from distribution.
Canada and a number of countries have suspended use of two types of Novartis flu vaccines in the past week after Italian authorities ordered the company to stop distribution of the products in Italy.
The two brands of flu vaccine are made at Novartis's production facility in Italy; they are sold under the names Agriflu and Fluad in Canada.
The Italian action came after Novartis informed the regulator that it had found protein aggregates in one batch of vaccine.
Dr. Vas Narasimhan says Novartis held back the affected lot and hasn't seen the problem in other batches of vaccines produced at the Italian facility.
Narasimhan says from time to time the proteins in flu vaccine fall out of suspension, but generally will disappear if the vaccine is shaken, as directed, before use.
He says flu vaccine always comes with instructions that the product should be shaken before injected. If particles are seen after the vaccine is shaken, doctors are advised not to use that dose or vial.
In testing that Novartis has done, the aggregates in the affected vaccine go back into solution with shaking, says Narasimhan, the global head of vaccines development for Novartis Vaccines and Diagnostics.
"We think that depending on temperature, depending on pH, depending on the strain we happen to use in a given year, you can see low levels of aggregates form on occasion. But generally speaking, these should go back into solution when shaken," he said in an interview from Cambridge, Mass.
Narasimhan says potency and safety testing Novartis conducted on all batches of Fluad and Agriflu showed all of the lots met safety and potency specifications.
Protein aggregates are the bits of the killed viruses that are used in flu vaccine to provoke the immune system to produce antibodies against the strains included in the shot. If a vaccinated person comes in contact with flu viruses, those antibodies should kick into gear to prevent infection.
The proteins used in flu vaccine are mainly hemagglutinin and neuraminidase, the two proteins that sit on the outside shell of a flu virus.
A number of European countries that purchase Novartis vaccines made at the Italian plant have suspended use of the products while the issue is being resolved. Those countries include Spain, Germany, Switzerland and France.
The United States has not been affected by the issue. While it purchased Novartis vaccine this season, the product it bought, Fluvirin, is made at a plant in Liverpool, England.