An inactivated influenza virus preparation is described which comprises a haemagglutinin antigen stabilized in the absence of thiomersal, or at low levels of thiomersal, wherein the haemagglutinin is detectable by a SRD assay. The influenza virus preparation may comprise a micelle modifying excipient, for example .alpha.-tocopherol or a derivative thereof in a sufficient amount to stabilize the haemagglutinin.

Description of the Invention

This application is a National Stage Entry of PCT/EP02/05883, filed May 29, 2002.

This invention relates to novel influenza virus antigen preparations, methods for preparing them and their use in prophylaxis or therapy. In particular the invention relates to inactivated influenza vaccines which are disrupted rather than whole virus vaccines and which are stable in the absence of organomercurial preservatives. Moreover, the vaccines contain haemagglutinin which is stable according to standard tests. The vaccines can be administered by any route suitable for such vaccines, such as intramuscularly, subcutaneously, intradermally or mucosally e.g. intranasally.

Influenza virus is one of the most ubiquitous viruses present in the world, affecting both humans and livestock. The economic impact of influenza is significant.

The influenza virus is an RNA enveloped virus with a particle size of about 125 nm in diameter. It consists basically of an internal nucleocapsid or core of ribonucleic acid (RNA) associated with nucleoprotein, surrounded by a viral envelope with a lipid bilayer structure and external glycoproteins. The inner layer of the viral envelope is composed predominantly of matrix proteins and the outer layer mostly of host-derived lipid material. The surface glycoproteins neuraminidase (NA) and haemagglutinin (HA) appear as spikes, 10 to 12 nm long, at the surface of the particles. It is these surface proteins, particularly the haemagglutinin, that determine the antigenic specificity of the influenza subtypes.

Currently available influenza vaccines are either inactivated or live attenuated influenza vaccine, Inactivated flu vaccines are composed of three possible forms of antigen preparation: inactivated whole virus, sub-virions where purified virus particles are disrupted with detergents or other reagents to solubilise the lipid envelope (so-called "split" vaccine) or purified HA and NA (subunit vaccine). These inactivated vaccines are given intramuscularly (i.m.) or intranasally (i.n.). There is no commercially available live attenuated vaccine.

Influenza vaccines, of all kinds, are usually trivalent vaccines. They generally contain antigens derived from two influenza A virus strains and one influenza B strain. A standard 0.5 ml injectable dose in most cases contains 15 .mu.g of haemagglutinin antigen component from each strain, as measured by single radial immunodiffusion (SRD) (J. M. Wood et al.: An improved single radial immunodiffusion technique for the assay of influenza haemagglutinin antigen: adaptation for potency determination of inactivated whole virus and subunit vaccines. J. Biol. Stand. 5 (1977) 237-247; J. M. Wood et al., International collaborative study of single radial diffusion and immunoelectrophoresis techniques for the assay of haemagglutinin antigen of influenza virus. J. Biol. Stand. 9 (1981) 317-330).

The influenza virus strains to be incorporated into influenza vaccine each season are determined by the World Health Organisation in collaboration with national health authorities and vaccine manufacturers.

Typical influenza epidemics cause increases in incidence of pneumonia and lower respiratory disease as witnessed by increased rates of hospitalisation or mortality. The elderly or those with underlying chronic diseases are most likely to experience such complications, but young infants also may suffer severe disease. These groups in particular therefore need to be protected.

Current efforts to control the morbidity and mortality associated with yearly epidemics of influenza are based on the use of intramuscularly administered inactivated influenza vaccines. The efficacy of such vaccines in preventing respiratory disease and influenza complications ranges from 75% in healthy adults to less than 50% in the elderly.

Standards are applied internationally to measure the efficacy of influenza vaccines. The European Union official criteria for an effective vaccine against influenza are set out in the table (see Original Patent). Theoretically, to meet the European Union requirements, an influenza vaccine has to meet only one of the criteria in the table, for all strains of influenza included in the vaccine. However in practice, at least two or all three of the criteria will need to be met for all strains, particularly for a new vaccine such as a new vaccine for delivery via a different route. Under some circumstances two criteria may be sufficient. For example, it may be acceptable for two of the three criteria to be met by all strains while the third criterion is met by some but not all strains (e.g. two out of three strains). The requirements are different for adult populations (18-60 years) and elderly populations (>60 years).

For a novel flu vaccine to be commercially useful it will not only need to meet those standards, but also in practice it will need to be at least as efficacious as the currently available injectable vaccines. It will also need to be commercially viable in terms of the amount of antigen and the number of administrations required.

The current commercially available influenza vaccines are either split or subunit injectable vaccines. These vaccines are prepared by disrupting the virus particle, generally with an organic solvent or a detergent, and separating or purifying the viral proteins to varying extents. Split vaccines are prepared by fragmentation of whole influenza virus, either infectious or inactivated, with solubilizing concentrations of organic solvents or detergents and subsequent removal of the solubilizing agent and some or most of the viral lipid material. Split vaccines generally contain contaminating matrix protein and nucleoprotein and sometimes lipid, as well as the membrane envelope proteins. Split vaccines will usually contain most or all of the virus structural proteins although not necessarily in the same proportions as they occur in the whole virus. Subunit vaccines on the other hand consist essentially of highly purified viral surface proteins, haemagglutinin and neuraminidase, which are the surface proteins responsible for eliciting the desired virus neutralising antibodies upon vaccination.

Many vaccines which are currently available require a preservative to prevent deterioration. A frequently used preservative is thimerosal which is a mercury-containing compound. Some public concerns have been expressed about the effects of mercury containing compounds. There is no surveillance system in place to detect the effects of low to moderate doses of organomercurials on the developing nervous system, and special studies of children who have received high doses of organomercurials will take several years to complete. Certain commentators have stressed that the potential hazards of thimerosal-containing vaccines should not be overstated (Offit; P.A. JAMA Vol. 283; No: 16). Nevertheless, it would be advantageous to find alternative methods for the preparation of vaccines to replace the use of thiomerosal in the manufacturing process. There is thus a need to develop vaccines which are thimerosal-free, in particular vaccines like influenza vaccines which are recommended, at least for certain population groups, on an annual basis.

It has been standard practice to date to employ a preservative for commercial inactivated influenza vaccines, during the production/purification process and/or in the final vaccine. The preservative is required to prevent microorganisms from growing through the various stages of purification. For egg-derived influenza vaccines, thiomersal is typically added to the raw allantoic fluid and may also be added a second time during the processing of the virus. Thus there will be residual thiomersal present at the end of the process, and this may additionally be adjusted to a desirable preservative concentration in the final vaccine, for example to a concentration of around 100 .mu.g/ml.

A side-effect of the use of thiomersal as a preservative in flu vaccines is a stabilisation effect. The thiomersal in commercial flu vaccines acts to stabilise the HA component of the vaccine, in particular but not exclusively HA of B strain influenza. Certain A strain haemagglutinins e.g. H3 may also require stabilisation. Therefore, although it may be desirable to consider removing thiomersal from influenza vaccines, or at least reducing the concentration of the thiomersal in the final vaccine, there is a problem to overcome in that, without thiomersal, the HA will not be sufficiently stable.

It has been discovered in the present invention that it is possible to stabilise HA in inactivated influenza preparations using alternative reagents that do not contain organomercurials. The HA remains stabilised such that it is detectable over time by quantitative standard methods, in particular SRD, to an greater extent than a non-stabilised antigen preparation produced by the same method but without stabilising excipient. The SRD method is performed as described hereinabove. Importantly, the HA remains stabilised for up to 12 months which is the standard required of a final flu vaccine.

DESCRIPTION OF THE INVENTION

In a first aspect the present invention provides an inactivated influenza virus preparation comprising a haemagglutinin antigen stabilised in the absence of thiomersal, or at low levels of thiomersal, wherein the haemagglutinin is detectable by a SRD assay.

Low levels of thiomersal are those levels at which the stability of HA derived from influenza B is reduced, such that a stabilising excipient is required for stabilised HA. Low levels of thiomersal are generally 5 .mu.g/ml or less.

Generally, stabilised HA refers to HA which is detectable over time by quantitative standard methods, in particular SRD, to a greater extent than a non-stabilised antigen preparation produced by the same method but without any stabilising excipient. Stabilisation of HA preferably maintains the activity of HA substantially constant over a one year period. Preferably, stabilisation allows the vaccine comprising HA to provide acceptable protection after a 6 month storage period, more preferably a one year period.

Suitably, stabilisation is carried out by a stabilising excipient, preferably a micelle modifying excipient. A micelle modifying excipient is generally an excipient that may be incorporated into a micelle formed by detergents used in, or suitable for, solubilising the membrane protein HA, such as the detergents Tween 80, Triton X100 and deoxycholate, individually or in combination.

Without wishing to be constrained by theory, it is believed that the excipients work to stabilise HA by interaction with the lipids, detergents and/or proteins in the final preparation. Mixed micelles of excipient with protein and lipid may be formed, such as micelles of Tween and deoxycholate with residual lipids and/or Triton X-100. It is thought that surface proteins are kept solubilised by those complex micelles. Preferably, protein aggregation is limited by charge repulsion of micelles containing suitable excipients, such as micelles containing negatively charged detergents.

Suitable micelle modifying excipients include: positively, negatively or zwitterionic charged amphiphilic molecules such as alkyl sulfates, or alkyl-aryl-sulfates; non-ionic amphiphilic molecules such as alkyl polyglycosides or derivatives thereof, such as Plantacare.RTM. (available from Henkel KGaA), or alkyl alcohol poly alkylene ethers or derivatives thereof such as Laureth-9.

Preferred excipients are .alpha.-tocopherol, or derivatives of .alpha.-tocopherol such as .alpha.-tocopherol succinate. Other preferred tocopherol derivatives for use in the invention include D-.alpha. tocopherol, D-.delta. tocopherol, D-.gamma. tocopherol and DL-.alpha.-tocopherol. Preferred derivatives of tocopherols that may be used include acetates, succinates, phosphoric acid esters, formiates, propionates, butyrates, sulfates and gluconates. Alpha-tocopherol succinate is particularly preferred. The .alpha.-tocopherol or derivative is present in an amount sufficient to stabilise the haemagglutinin.

Other suitable excipients may be identified by methods standard in the art, and tested for example using the SRD method for stability analysis as described herein.

In a preferred aspect the invention provides an influenza virus antigen preparation comprising at least one stable influenza B strain haemagglutinin antigen.

The invention provides in a further aspect a method for preparing a stable haemagglutinin antigen which method comprises purifying the antigen in the presence of a stabilising micelle modifying excipient, preferably .alpha.-tocopherol or a derivative thereof such as .alpha.-tocopherol succinate.

Further provided by the invention are vaccines comprising the antigen preparations described herein and their use in a method for prophylaxis of influenza infection or disease in a subject which method comprises administering to the subject a vaccine according to the invention.

The vaccine may be administered by any suitable delivery route, such as intradermal, mucosal e.g. intranasal, oral, intramuscular or subcutaneous. Other delivery routes are well known in the art.

Intradermal delivery is preferred. Any suitable device may be used for intradermal delivery, for example short needle devices such as those described in U.S. Pat. No. 4,886,499, U.S. Pat. No. 5,190,521, U.S. Pat. No. 5,328,483, U.S. Pat. No. 5,527,288, U.S. Pat. No. 4,270,537, U.S. Pat. No. 5,015,235, U.S. Pat. No. 5,141,496, U.S. Pat. No. 5,417,662. Intradermal vaccines may also be administered by devices which limit the effective penetration length of a needle into the skin, such as those described in WO99/34850 and EP1092444, incorporated herein by reference, and functional equivalents thereof. Also suitable are jet injection devices which deliver liquid vaccines to the dennis via a liquid jet injector or via a needle which pierces the stratum corneum and produces a jet which reaches the dermis. Jet injection devices are described for example in U.S. Pat. No. 5,430,381, U.S. Pat. No. 5,599,302, U.S. Pat. No. 5,334,144, U.S. Pat. No. 5,993,412. U.S. Pat. No. 5,649,912, U.S. Pat. No. 5,569,489, U.S. Pat. No. 5,704,911, U.S. Pat. No. 5,383,351, U.S. Pat. No. 5,893,397, U.S. Pat. No. 5,466,220, U.S. Pat. No. 5,339,163, U.S. Pat. No. 5,312,335, U.S. Pat. No. 5,503,627, U.S. Pat. No. 5,064,413, U.S. Pat. No. 5,520,639, U.S. Pat. No. 4,596,556, U.S. Pat. No. 4,790,824, U.S. Pat. No. 4,941,880, U.S. Pat. No. 4,940,460, WO 97/37705 and WO 97/13537.

Also suitable are ballistic powder/particle delivery devices which use compressed gas to accelerate vaccine in powder form through the outer layers of the skin to the dermis. Additionally, conventional syringes may be used in the classical mantoux method of intradermal administration. However, the use of conventional syringes requires highly skilled operators and thus devices which are capable of accurate delivery without a highly skilled user are preferred.

The invention thus provides a method for the prophylaxis of influenza infection or disease in a subject which method comprises administering to the subject intradermally an influenza vaccine according to the invention.

The invention also extends to intradermal devices in combination with a vaccine according to the present invention, in particular with devices disclosed in WO99/34850 or EP1092444, for example.

Also provided is the use of a micelle modifying excipient, preferably .alpha.-tocopherol or a derivative thereof as a haemagglutinin stablilser in the manufacture of an influenza vaccine.

The invention applies particularly but not exclusively to the stabilisation of B strain influenza haemagglutinin.

Preferably the stabilised HA of the present invention is stable for 6 months, more preferably 12 months.

Preferably the .alpha.-tocopherol is in the form of an ester, more preferably the succinate or acetate and most preferably the succinate.

Preferred concentrations for the .alpha.-tocopherol or derivative are between 1 .mu.g/ml-10 mg/ml, more preferably between 10 .mu.g/ml-500 .mu.g/ml.

The vaccine according to the invention generally contains both A and B strain virus antigens, typically in a trivalent composition of two A strains and one B strain. However, divalent and monovalent vaccines are not excluded. Monovalent vaccines may be advantageous in a pandemic situation, for example, where it is important to get as much vaccine produced and administered as quickly as possible.

The non-live flu antigen preparation for use in the invention may be selected from the group consisting of split virus antigen preparations, subunit antigens (either recombinantly expressed or prepared from whole virus), inactivated whole virus which may be chemically inactivated with e.g. formaldehyde, .beta.-propiolactone or otherwise inactivated e.g. U.V. or heat inactivated. Preferably the antigen preparation is either a split virus preparation, or a subunit antigen prepared from whole virus, particularly by a splitting process followed by purification of the surface antigen. Most preferred are split virus preparations.

Preferably the concentration of haemagglutinin antigen for each strain of the influenza virus preparation is 1-1000 .mu.g per ml, more preferably 3-300 .mu.g per ml and most preferably about 30 .mu.g per ml, as measured by a SRD assay.

The vaccine according to the invention may further comprise an adjuvant or immunostimulant such as but not limited to detoxified lipid A from any source and non-toxic derivatives of lipid A, saponins and other reagents capable of stimulating a TH1 type response.

It has long been known that enterobacterial lipopolysaccharide (LPS) is a potent stimulator of the immune system, although its use in adjuvants has been curtailed by its toxic effects. A non-toxic derivative of LPS, monophosphoryl lipid A (MPL), produced by removal of the core carbohydrate group and the phosphate from the reducing-end glucosamine, has been described by Ribi et al (1986, Immunology and Immunopharmacology of bacterial endotoxins, Plenum Publ. Corp., NY, p 407-419) and has the following structure -- see Original Patent.

A further detoxified version of MPL results from the removal of the acyl chain from the 3-position of the disaccharide backbone, and is called 3-O-Deacylated monophosphoryl lipid A (3D-MPL). It can be purified and prepared by the methods taught in GB 2122204B, which reference also discloses the preparation of diphosphoryl lipid A, and 3-O-deacylated variants thereof.

A preferred form of 3D-MPL is in the form of an emulsion having a small particle size less than 0.2 .mu.m in diameter, and its method of manufacture is disclosed in WO 94/21292. Aqueous formulations comprising monophosphoryl lipid A and a surfactant have been described in WO9843670A2.

The bacterial lipopolysaccharide derived adjuvants to be formulated in the compositions of the present invention may be purified and processed from bacterial sources, or alternatively they may be synthetic. For example, purified monophosphoryl lipid A is described in Ribi et al 1986 (supra), and 3-O-Deacylated monophosphoryl or diphosphoryl lipid A derived from Salmonella sp. is described in GB 2220211 and U.S. Pat. No. 4,912,094. Other purified and synthetic lipopolysaccharides have been described (Hilgers et al., 1986, Int.Arch.Allergy.Immunol., 79(4):392-6; Hilgers et al., 1987, Immunology, 60(1):141-6; and EP 0 549 074 B1). A particularly preferred bacterial lipopolysaccharide adjuvant is 3D-MPL.

Accordingly, the LPS derivatives that may be used in the present invention are those immunostimulants that are similar in structure to that of LPS or MPL or 3D-MPL. In another aspect of the present invention the LPS derivatives may be an acylated monosaccharide, which is a sub-portion to the above structure of MPL.

Saponins are taught in: Lacaille-Dubois, M and Wagner H. (1996. A review of the biological and pharmacological activities of saponins. Phytomedicine vol 2 pp 363-386). Saponins are steroid or triterpene glycosides widely distributed in the plant and marine animal kingdoms. Saponins are noted for forming colloidal solutions in water which foam on shaking, and for precipitating cholesterol. When saponins are near cell membranes they create pore-like structures in the membrane which cause the membrane to burst. Haemolysis of erythrocytes is an example of this phenomenon, which is a property of certain, but not all, saponins.

Saponins are known as adjuvants in vaccines for systemic administration. The adjuvant and haemolytic activity of individual saponins has been extensively studied in the art (Lacaille-Dubois and Wagner, supra). For example, Quil A (derived from the bark of the South American tree Quillaja Saponaria Molina), and fractions thereof, are described in U.S. Pat. No. 5,057,540 and "Saponins as vaccine adjuvants", Kensil, C. R., Crit Rev Ther Drug Carrier Syst, 1996, 12 (1-2):1-55; and EP 0 362 279 B1. Particulate structures, termed Immune Stimulating Complexes (ISCOMS), comprising fractions of Quil A are haemolytic and have been used in the manufacture of vaccines (Morein, B., EP 0 109 942 B1; WO 96/11711; WO 96/33739). The haemolytic saponins QS21 and QS17 (HPLC purified fractions of Quil A) have been described as potent systemic adjuvants, and the method of their production is disclosed in U.S. Pat. No. 5,057,540 and EP 0 362 279 B1. Other saponins which have been used in systemic vaccination studies include those derived from other plant species such as Gypsophila and Saponaria (Bomford et al., Vaccine, 10(9):572-577, 1992).

An enhanced system involves the combination of a non-toxic lipid A derivative and a saponin derivative particularly the combination of QS21 and 3D-MPL as disclosed in WO 94/00153, or a less reactogenic composition where the QS21 is quenched with cholesterol as disclosed in WO 96/33739.

A particularly potent adjuvant formulation involving QS21 and 3D-MPL in an oil in water emulsion is described in WO 95/17210 and is a preferred formulation.

Accordingly in one embodiment of the present invention there is provided a vaccine comprising an influenza antigen preparation of the present invention adjuvanted with detoxified lipid A or a non-toxic derivative of lipid A, more preferably adjuvanted with a monophosphoryl lipid A or derivative thereof.

Preferably the vaccine additionally comprises a saponin, more preferably QS21.

Preferably the formulation additionally comprises an oil in water emulsion. The present invention also provides a method for producing a vaccine formulation comprising mixing an antigen preparation of the present invention together with a pharmaceutically acceptable excipient, such as 3D-MPL.

The vaccines according to the invention may further comprise at least one surfactant which may be in particular a non-ionic surfactant. Suitable non-ionic surfactants are selected from the group consisting of the octyl- or nonylphenoxy polyoxyethanols (for example the commercially available Triton.TM. series), polyoxyethylene sorbitan esters (Tween.TM. series) and polyoxyethylene ethers or esters of general formula (I): HO(CH.sub.2CH.sub.2O).sub.n-A-R (I) wherein n is 1-50, A is a bond or --C(O)--, R is C.sub.1-50 alkyl or phenyl C.sub.1-50 alkyl; and combinations of two or more of these.

Preferred surfactants falling within formula (I) are molecules in which n is 4-24, more preferably 6-12, and most preferably 9; the R component is C.sub.1-50, preferably C.sub.4-C.sub.20 alkyl and most preferably C.sub.12 alkyl.

Octylphenoxy polyoxyethanols and polyoxyethylene sorbitan esters are described in "Surfactant systems" Eds: Attwood and Florence (1983, Chapman and Hall). Octylphenoxy polyoxyethanols (the octoxynols), including t-octylphenoxypolyethoxyethanol (Triton X-100.TM.) are also described in Merck Index Entry 6858 (Page 1162, 12.sup.th Edition, Merck & Co. Inc., Whitehouse Station, N.J., USA; ISBN 0911910-12-3). The polyoxyethylene sorbitan esters, including polyoxyethylene sorbitan monooleate (Tween 80.TM.) are described in Merck Index Entry 7742 (Page 1308, 12.sup.th Edition, Merck & Co. Inc., Whitehouse Station, N.J., USA; ISBN 0911910-12-3). Both may be manufactured using methods described therein, or purchased from commercial sources such as Sigma Inc.

Particularly preferred non-ionic surfactants include Triton X-45, t-octylphenoxy polyethoxyethanol (Triton X-100), Triton X-102, Triton X-114, Triton X-165, Triton X-205, Triton X-305, Triton N-57, Triton N-101, Triton N-128, Breij 35, polyoxyethylene-9-lauryl ether (laureth 9) and polyoxyethylene-9-stearyl ether (steareth 9). Triton X-100 and laureth 9 are particularly preferred. Also particularly preferred is the polyoxyethylene sorbitan ester, polyoxyethylene sorbitan monooleate (Tween 80.TM.).

Further suitable polyoxyethylene ethers of general formula (I) are selected from the following group: polyoxyethylene-8-stearyl ether, polyoxyethylene-4-lauryl ether, polyoxyethylene-35-lauryl ether, and polyoxyethylene-23-lauryl ether.

Alternative terms or narnes for polyoxyethylene lauryl ether are disclosed in the CAS registry. The CAS registry number of polyoxyethylene-9 lauryl ether is: 9002-92-0. Polyoxyethylene ethers such as polyoxyethylene lauryl ether are described in the Merck index (12.sup.th ed: entry 7717, Merck & Co. Inc., Whitehouse Station, N.J., USA; ISBN 0911910-12-3). Laureth 9 is formed by reacting ethylene oxide with dodecyl alcohol, and has an average of nine ethylene oxide units.

Two or more non-ionic surfactants from the different groups of surfactants described may be present in the vaccine formulation described herein. In particular, a combination of a polyoxyethylene sorbitan ester such as polyoxyethylene sorbitan monooleate (Tween 80.TM.) and an octoxynol such as t-octylphenoxypolyethoxyethanol (Triton) X-100.TM. is preferred. Another particularly preferred combination of non-ionic surfactants comprises laureth 9 plus a polyoxyethylene sorbitan ester or an octoxynol or both.

Non-ionic surfactants such as those discussed above have preferred concentrations in the final vaccine composition as follows: polyoxyethylene sorbitan esters such as Tween 80.TM.: 0.01 to 1%, most preferably about 0.1% (w/v); octyl- or nonylphenoxy polyoxyethanols such as Triton X-100.TM. or other detergents in the Triton series: 0.001 to 0.1%, most preferably 0.005 to 0.02% (w/v); polyoxyethylene ethers of general formula (I) such as laureth 9: 0.1 to 20%, preferably 0.1 to 10% and most preferably 0.1 to 1% or about 0.5% (w/v).

For certain vaccine formulations, other vaccine components may be included in the formulation. As such the formulations of the present invention may also comprise a bile acid or a derivative thereof, in particular in the form of a salt. These include derivatives of cholic acid and salts thereof, in particular sodium salts of cholic acid or cholic acid derivatives. Examples of bile acids and derivatives thereof include cholic acid, deoxycholic acid, chenodeoxycholic acid, lithocholic acid, ursodeoxycholic acid, hyodeoxycholic acid and derivatives such as glyco-, tauro-, amidopropyl-1-propanesulfonic-, amidopropyl-2-hydroxy-1-propanesulfonic derivatives of the aforementioned bile acids, or N,N-bis (3Dgluconoamidopropyl) deoxycholamide. A particularly preferred example is sodium deoxycholate (NaDOC) which may be present in the final vaccine dose.

Also provided by the invention are pharmaceutical kits comprising a vaccine administration device filled with a vaccine according to the invention. Such administration devices include but are not limited to needle devices, liquid jet devices, powder devices, and spray devices (for intranasal use).

The influenza virus antigen preparations according to the invention may be derived from the conventional embryonated egg method, or they may be derived from any of the new generation methods using tissue culture to grow the virus or express recombinant influenza virus surface antigens. Suitable cell substrates for growing the virus include for example dog kidney cells such as MDCK or cells from a clone of MDCK, MDCK-like cells, monkey kidney cells such as AGMK cells including Vero cells, suitable pig cell lines, or any other mammalian cell type suitable for the production of influenza virus for vaccine purposes. Suitable cell substrates also include human cells e.g. MRC-5 cells. Suitable cell substrates are not limited to cell lines; for example primary cells such as chicken embryo fibroblasts are also included.

The influenza virus antigen preparation may be produced by any of a number of commercially applicable processes, for example the split flu process described in patent no. DD 300 833 and DD 211 444, incorporated herein by reference. Traditionally split flu was produced using a solvent/detergent treatment, such as tri-n-butyl phosphate, or diethylether in combination with Tween.TM. (known as "Tween-ether" splitting) and this process is still used in some production facilities. Other splitting agents now employed include detergents or proteolytic enzymes or bile salts, for example sodium deoxycholate as described in patent no. DD 155 875, incorporated herein by reference. Detergents that can be used as splitting agents include cationic detergents e.g. cetyl trimethyl ammonium bromide (CTAB), other ionic detergents e.g. laurylsulfate, taurodeoxycholate, or non-ionic detergents such as the ones described above including Triton X-100 (for example in a process described in Lina et al, 2000, Biologicals 28, 95-103) and Triton N-101, or combinations of any two or more detergents.

The preparation process for a split vaccine will include a number of different filtration and/or other separation steps such as ultracentrifugation, ultrafiltration, zonal centrifugation and chromatography (e.g ion exchange) steps in a variety of combinations, and optionally an inactivation step, e.g., with heat, formaldehyde or .beta.-propiolactone or U.V. which may be carried out before or after splitting. The splitting process may be carried our as a batch, continuous or semi-continuous process.

Preferred split flu vaccine antigen preparations according to the invention comprise a residual amount of Tween 80 and/or Triton X-100 remaining from the production process, although these may be added or their concentrations adjusted after preparation of the split antigen. Preferably both Tween 80 and Triton X-100 are present. The preferred ranges for the final concentrations of these non-ionic surfactants in the vaccine dose are: Tween 80: 0.01 to 1%, more preferably about 0.1% (v/v) Triton X-100: 0.001 to 0.1 (% w/v), more preferably 0.005 to 0.02% (w/v).

Alternatively the influenza virus antigen preparations according to the invention may be derived from a source other than the live influenza virus, for example the haemagglutinin antigen may be produced recombinantly.

Claim 1 of 16 Claims

1. An aqueous, inactivated influenza virus preparation comprising a haemagglutinin antigen (HA) stabilised in the absence of thiomersal, or at a level of thiomersal of 5 .mu.g/ml or less, wherein the HA is detectable by a Single Radial Immunodiffusion (SRD) assay, wherein the preparation comprises .alpha.-tocopherol succinate in a sufficient amount to stabilise the HA.

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