The WHO makes a decision in February of each year on the influenza strains to be included in the following winter’s vaccine for the Northern Hemisphere, and in August for the Southern Hemisphere. The WHO Collaborating Centres then release suitable prototype viruses (“primary seed”) to the manufacturers, of which Solvay Biologicals is one. These prototype viruses, currently comprising three influenza virus strains, were originally isolated from humans suffering from influenza.
In Solvay’s laboratories, each of the primary seed virus strains – one A-H3N2, one A-H1N1, and one B strain – are separately propagated in hens’ eggs to produce larger amounts of the viruses, called the working seed virus stock. This secondary seed virus then serves as source for the production of virus batches on a large, industrial scale.
The Influvac® production line starts with the injection of the secondary seed virus into embryonated chicken eggs. In this process, millions of 10- to 11-day-old embryonated eggs are automatically inoculated with a small amount of secondary seed virus. These eggs are from healthy flocks, and their outer shell surface, which is naturally contaminated with bacteria, has been washed with a disinfectant before inoculation. Viruses can only grow on live cells. After an incubation of three days at a temperature of 32 to 36 degrees Celsius, the liquid containing the virus particles is extracted from the eggs. Following inactivation of the viral RNA, the virus is clarified by centrifuge to remove large impurities and ultra-centrifuged to obtain a highly purified virus suspension. The viruses are now “dead”, i.e., they cannot replicate any more. Then CTAB detergent is used for to remove hemagglutinin and neuraminidase (the “subunits”) from the viral membrane. These subunits are separated from the membrane and the viral core by another ultra-centrifugation. These production steps are applied separately for each of the three vaccine components.(also see flowchart on the bottom of this page )
In a last step, the components are combined in the correct proportion, and the mixture is filled into syringes of 0.5 ml. A syringe contains one dose of trivalent influenza vaccine in the required amount of 15 µg HA per strain (thus, 3 x 15 µg = 45 µg HA in total). Finally, the vaccine is tested and then marketed after approval by the Authorities in the country in question.
To prevent contamination precautions are taken during filling of the syringes. Filling of the syringes is done in an isolator. An isolator is a closed unit and everything that enters the isolator is sterilized. In this way the sterility of the filling environment is secured and the chances of bacterial contamination are eliminated.
Solvay introduced a new low-volume packaging in 2005. Pre-filled syringes packed as singles or in trays of ten.
In this way, Solvay Biologicals produces many million doses of influenza vaccines each year. The vaccine has to meet strict, high quality requirements. Nowadays, there is a central registration procedure for the new vaccine for all member states of the European Community. To guarantee a timely distribution of the vaccine, both the manufacturers and the registration authorities are under great time pressure to meet all the requirements for approval. Once vaccine production is underway, this annual registration procedure is initiated. As soon as the first vaccine batch has been produced, two clinical studies on this material are done among young and elderly adults to confirm tolerance and effectiveness. Each batch is tested and released by Solvay and the authorities.
Flowchart of Influenza vaccine production:
