By IANS,
New Delhi : Developing vaccines against swine flu virus strains is a complex and time-consuming process and inoculations are usually effective only for a single season, says an expert at a leading vaccine-producing institute in Pune.
Influenza viruses change frequently and hence a vaccine made against a specific strain is useful only for vaccination during a single season, said Rajeev M. Dhere, senior director with the Serum Institute.
The seasonal vaccine production for the influenza viruses, expected to be active in the winter of 2009, is almost fully ready and stocked up in major consumption areas of the world, Dhere told the Indian edition of Technology Review, the 109-year old magazine of the Massachusetts Institute of Technology published by CyberMedia.
Experts like him also indicated that the current year’s seasonal influenza vaccine has used three virus strains – A/Brisbane/59/2007 (H1N1), A/Uruguay/716/2007 (H3N2) and B/Florida/4/2006.
Dhere says experts at the Atlanta-based Center for Disease Control have determined the genetic sequence of the new H1N1 influenza virus.
“The genetic sequence is significantly different to the H1N1 contained in the current seasonal influenza vaccine. So the current seasonal vaccines will not provide any protection against the new H1N1 strain. Hence, a different vaccine is required.”
Several strains of the H1N1 viruses have been extracted from infected people in Mexico and California. The A/Mexico and A/California strains are the basis for the vaccine production.
Dhere also explains the process:
-First the “seed” virus is made for which experts at the Atlanta-based institute have used A/Mexico and A/California H1N1 strains. The seed virus is a safe form of the influenza virus, stripped of its parts that spread the infection
-Then the live virus is genetically altered to make it safe. This is a time-consuming process and takes about three-four weeks. This seed virus is supplied to vaccine manufacturers chosen by the World Health Organisation around the world
-The seed viruses from various strains are then prepared to be ready for vaccine production by a process called “assortment.” These re-assorted viruses are then injected into specially prepared pathogen – or germ-free – fertile chicken eggs
-The safe virus then grows inside the eggs for four-six weeks. The viruses are then extracted from the eggs, purified, inactivated and then formulated into a vaccine
Serum Institute in Pune has already received the seed viruses, even as the H1N1 strains have been extracted from infected patients in India and Turkey.
Thankfully, the experts have found that the viruses are identical, indicating that the new vaccine should work against the swine flu that has spread to all these regions.
The normal dosage of influenza vaccine is 15 mg. From each chicken egg, one dose of influenza vaccine is produced. Sometimes, two eggs may be required to produce each dose of standard influenza vaccine.