What is an influenza vaccine?
Influenza vaccines licensed in the EU consist of killed influenza virus suspended in an inert buffer solution to maintain stability. The vaccine is trivalent, i.e. it contains three different strains of influenza – A(H1N1), A(H3N2) and B. Some specialised influenza vaccines might also contain an adjuvant – a compound designed to help stimulate the immune system. Large quantities of virus are required to prepare the hundreds of millions of doses of flu vaccine manufactured every year. These quantities of virus are generally grown in hens’ eggs, although the use of cell cultures as an alternative is under development. In order to reduce the incidence of side reactions from vaccination, the virus is then purified and split apart using a detergent. Some vaccine manufacturers process their vaccine further by separating out the surface antigens of the virus (the components crucial for the vaccine) from the rest of the virus. During processing, the virus is chemically inactivated so that it can no longer cause disease. This is achieved in part by treatment with detergent and also by treating the virus with an inactivating substance such as formaldehyde. The entire process has to be performed with great care in order to preserve the immunogenic properties of the vaccine.
NIBSC does not make influenza vaccine; this is made by vaccine manufacturers. NIBSC supplies the vaccine manufacturers with the strains of virus used to make vaccine. It also prepares and supplies the reagents needed by the manufacturers to quantify each dose of their vaccine.
Which influenza virus is used to make vaccine?
Due to a process called antigenic drift, whereby influenza viruses constantly undergo mutation of their coat proteins (the ones recognised by the immune system), influenza viruses are kept under constant surveillance. Twice a year, the World Health Organisation (WHO), based in Geneva, organises a consultation with the Directors of the WHO Influenza Collaborating Centres and representatives of Essential Regulatory Laboratories to review the results of laboratory and clinical studies of influenza viruses circulating in the community and to make recommendations on which strains should go into the vaccine – commonly referred to as the ‘composition’ of the influenza vaccine (February: northern hemisphere; September: southern hemisphere). WHO has described this process at http://www.who.int/csr/disease/influenza/vaccinerecommendations/en/ .
Invariably, the viruses recommended by WHO do not grow well in hens’ eggs so alternative viruses more suited to vaccine production must be sought. For influenza A viruses, it is usual to develop a high growth reassortant (hgr) between the WHO-recommended virus and a laboratory virus A/PR/8/34 which grows well in eggs. Such hgrs are currently produced by three laboratories (New York Medical College, USA and CSL, Australia and NIBSC) all funded by the vaccine industry. Reassortants are recognized by the following nomenclature: NYMC-xxx, IVR-xxx, or NIB-xxx. By use of hgrs it is possible to significantly increase the virus yield. Work is also in progress to develop high growth reassortants for B viruses. Usually two or three hgrs are produced for each newly recommended strain and within the EU there is a vaccine virus selection meeting held within the framework of the CHMP about one month after the WHO Recommendation in order to select the most appropriate vaccine virus for the EU. NIBSC coordinates the evaluation of candidate influenza vaccine viruses by EU vaccine manufacturers. Similar selection procedures also take place in the USA, Australia and Japan. If countries do not have such a process, they may choose to follow the decision made by another national or regional authority. NIBSC supplies candidate influenza vaccine viruses to manufacturers and laboratories located in over 20 countries, mostly within Europe, but also in North America, Asia and to Australia.
What is the purpose of the NIBSC influenza reagents?
NIBSC influenza reagents are designed for use in Single Radial Diffusion (SRD) assays. They consist of a calibrated freeze dried antigen prepared from the same strain of virus used in vaccines and a sheep antiserum raised to the purified influenza haemagglutinin. The NIBSC reagents are calibrated by a small collaborative study involving the Essential Regulatory Laboratories - NIBSC; CBER, USA; TGA, Australia and NIID, Japan. If the NIBSC influenza reagents are used for other purposes such as ELISA or Western blots, it should be borne in mind that the antisera are sometimes cross-reactive (to a low level) with other influenza proteins such as nucleoprotein. This does not normally interfere with SRD assays, but may be significant in other types of assays.
What is the normal titre of the NIBSC antigen reagents?
The antigen reagents are calibrated in terms of haemagglutinin antigen content. Their content is usually in the range 30-60 micrograms haemagglutinin activity. The antigens are not assayed for haemagglutinating activity. The antiserum reagents are assessed by SRD activity and not by haemagglutination-inhibition (HI) assay, but they are expected to have HI titres >1:5000.
How do I order influenza reference viruses and reagents?
Live influenza candidate vaccine viruses are available from NIBSC, but are not listed in the NIBSC catalogue. To place an order for a live influenza virus, email standards@hpa.nibsc.org.uk and a request form will be sent to you. Influenza reagents can be ordered in the usual manner from standards@hpa.nibsc.org.uk or on-line at http://www.nibsc.ac.uk/products/
How much will it cost to receive influenza reference viruses and reagents?
The handling charges for influenza reagents are described at http://www.nibsc.ac.uk/products/ . There are no handling charges for influenza candidate vaccine viruses viruses, but you will be asked to pay for packaging and courier charges. We will require a purchase order number from you on the virus request form as this will be used to prepare an invoice for the shipping costs.
Do I need an import permit to receive influenza reagents?
This depends on the local requirements in each importing country. In order to aid importation, NIBSC supplies information about the antigens used to produce the NIBSC antigen reagents and the sheep sera used to produce the NIBSC antiserum reagents in the ‘advice on importing influenza reagents’ on the NIBSC website and in the products’ Instructions for Use.
How long can I store a reconstituted antigen reagent?
It is recommended that, once reconstituted, the antigen reagents are not stored for subsequent use. You may wish to validate storage of reconstituted antigens in your laboratory, but that is your responsibility.
Do you have any publications on the Single Radial Diffusion assay?
This assay was developed at NIBSC in the late 1970’s and suitable publications illustrating its use are:
Pandemic Influenza
Where can I obtain information about the threat of pandemic influenza?
There are several excellent sites describing the current status of avian influenza outbreaks and the incidence of human cases of H5N1 infection. They include: HPA Influenza. WHO Avian Influenza. CDC Influenza.
Is there an effective vaccine against H5N1 virus in humans?
Vaccines effective against H5N1 virus are not yet available. Vaccines produced each year for seasonal influenza will not protect against pandemic influenza. Although vaccines against the H5N1 virus are under development in several countries, no vaccine is ready for commercial production and no vaccines are expected to be widely available until several months after the start of a pandemic. Many clinical trials are now under way to test whether experimental vaccines will be effective and to determine whether different formulations can economise on the amount of antigen required, thus boosting production capacity. Because the vaccine needs to closely match the pandemic virus, large-scale commercial production will not start until the new virus has emerged and a pandemic has been declared. Current global production capacity falls far short of the demand expected during a pandemic.
What candidate pandemic vaccine viruses are available?
WHO is urgently working together with laboratories in the WHO Influenza Network (including NIBSC) to develop candidate influenza H5N1 vaccine viruses for use by vaccine manufacturers. Details of these viruses and contact details for requests are available from the WHO . In addition, NIBSC is working with international partners to develop a library of potential pandemic viruses, which will include the H5, H2, H7, H9 subtypes ( Library of candidate influenza vaccine viruses and reagents ). If you would like to obtain candidate pandemic influenza vaccine viruses, we will need proof that a satisfactory level of containment is available to you, that you have the appropriate import permit and a brief description of the intended use of the viruses. In some cases (i.e. viruses derived by reverse genetics), a Materials Transfer Agreement must also be agreed before despatch of virus. Please contact NIBSC at standards@nibsc.hpa.org.uk and we will discuss it further.
Are there any reagents available for candidate pandemic vaccine viruses?
Yes, they are produced by NIBSC whenever a new candidate pandemic vaccine virus is produced at NIBSC. They are advertised on the NIBSC IRC website and further enquiries can be made at standards@nibsc.hpa.org.uk