1. Field of the Invention
The present invention relates to an improved calcium phosphate gel for the preparation of adsorbed vaccines. It includes the vaccines adsorbed by a novel gel of this kind.
2. Description of the Prior Art
The advantages of adsorbed vaccines are known. The concentrated form in which they may be present provides the advantage of only requiring a small space for their storage, whilst it is possible to prepare, when needed, large quantities of vaccines in very little time from this form. This is particularly valuable in the event of epidemics or other occurrences when the vaccines might be necessary immediately. The adsorbed preparations, which remain stable for several years, enable the need for control of their dilution products to be considerably reduced, since the necessary titrations have been carried out on the concentrated products.
For these reasons, the adsorbed vaccines have been the subject of various investigations, not all of which have led to satisfactory results. In fact, the majority of adsorbants which have been proposed have the drawback that they are irritants, that they exhibit poor adsorption of the antigens, or that they are difficult to adapt to an industrial scale preparation.
Some progress has been made with the use of a calcium phosphate gel prepared by the known method of Tiselius, that is to say, a gel formed of brushite wherein the phosphate is in the form of PO.sub.4 HCa.2H.sub.2 O. However, even in this form, the gel does not adsorb sufficient antigens in all cases of interest and quite often its deleterious properties leave much to be desired. A further improvement has ameliorated the vaccines adsorbed on calcium phosphate gel, i.e., the one which forms the subject of Belgian Pat. No. 721,141 or U.S. Pat. No. 3,608,071 and which consists of precipitating the phosphate within a medium containing the antigen. The gel still has the composition of brushite.