Production
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 Abbott Biologicals is one. These prototype viruses,
currently comprising three influenza virus strains, were originally isolated from
humans suffering from influenza.
In Abbott’s production 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.
Abbott introduced a new low-volume packaging
in 2005. Pre-filled syringes packed as singles or in trays of ten.
In this way, Abbott 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 Abbott and the authorities.
Flowchart of Influenza vaccine production:
