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Strategic FMD vaccine reserves have been in existence since the 1970s
as part of FMD control programmes. However, the shelf-life of conventional
formulated FMD vaccines is in the order of one year, and the cost of maintaining
these reserves by annual replacement is therefore high. In the
1970s, advances in technology prepared the ground for the introduction
of highly concentrated FMD antigen in low volumes stored at ultra-low
temperatures over liquid nitrogen or in -80ºC freezers. In this form antigens
appear to be extremely stable. Thus the three international FMD vaccine
banks comprise pretested FMD antigen concentrates of a spectrum of virus
types and subtypes which are stored for rapid formulation into vaccines
in the event of an FMD emergency situation. 'Strategic FMD Antigen Reserve'
is perhaps a more appropriate title for these banks.
The first essential component of an FMD antigen bank is the concentrated,
inactivated antigen supplied by a commercial source. The antigen needs
to be capable of producing a highly potent vaccine when reformulated.
Thus, the manufacturer should specify the expected dose volume to yield
a vaccine with minimum potency in excess of the commercial prophylactic
FMD vaccines.
The second element of an FMD antigen bank is a capacity to store the antigen
at ultra-low temperatures, either at -80ºC in freezers or over liquid
nitrogen at -130ºC.
The third essential element is the facility to reformulate the antigens
rapidly into potent vaccines. The three international banks have different
arrangements for this part of the process. The European Union Vaccine
Bank (EUVB) has an ad hoc arrangement to return the antigen to the manufacturer
for reformulation at 2.5 million doses over a 10-day period. The International
Vaccine Bank (IVB) maintains its own emergency manufacturing facility
to Good Manufacturing Practice (GMP) standards and holds both Product
and Manufacturing Licences for aqueous FMD vaccines. This facility can
manufacture up to 200,000 doses of vaccine over a 24-hour period. The
North American Vaccine Bank (NAVB) is seeking an arrangement with a commercial
FMD vaccine manufacturer to produce 2 million doses in the first week.
Once a vaccine has been manufactured, it must be appropriately labelled,
packaged and distributed. For the IVB this requires the storage of adequate
bottling, labelling and packaging materials and the reserve staff to perform
these tasks. Rapid distribution along a cold-chain is essential in view
of the relatively short shelf-life of some emergency vaccines and the
need for haste in the face of an FMD outbreak.
To ensure the continued stability and potency of the stored antigens,
a regular schedule of testing is required. Apart from the financial savings
made compared with the annual disposal of preformulated vaccines, other
advantages accrue for antigen reserves in terms of flexibility in formulation
for different species and the extra information that can be gained on
each antigen during its storage life, such as the expected level of protection
against heterologous strains of the same serotype. The potency, stability
and innocuity/sterility tests performed on the antigens during their storage
in the FMD banks allows retrospective potency/sterility tests to be performed
on the reformulated vaccines. This allows immediate despatch of the vaccines,
which is essential in the circumstances of reformulation.
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