Thermostability of poliovirus and measles vaccines.

Oral poliovirus vaccine, which has almost prevented the appearance of new poliomyelitis cases in the world, has been stabilized by incorporating molar MgCl2 into the vaccine. With the stabilizer, the virus can be held for years at 4 degrees C, and for six weeks at 22-25 degrees C, with no loss in titre. The stabilized virus loses 0.5 log10 units in three days at 37 degrees C, and in three hours at 45 degrees C. The MgCl2-stabilized vaccine, after being held at 30 degrees C for 21 days, elicited an antibody response in humans equal to that of standard vaccine maintained in the frozen state and thawed just before administration. The goal of WHO is to have a vaccine that does not lose any potency when held at 45 degrees C for at least seven days. Several approaches have been explored, with the addition of heavy water (Crainic et al, this volume) plus MgCl2 being the best. When poliovaccine is formulated with heavy water and MgCl2, it is more thermostable than in ordinary water containing molar MgCl2. Reconstituted measles vaccine rapidly loses potency at room temperature. At 22-25 degrees C, there is usually a 50% loss in potency in one hour, and at higher temperatures the reconstituted vaccine loses potency even more rapidly, and cannot be used. When molar MgSO4 is added, measles vaccine is stabilized, losing only 0.3 log10 in 30 minutes at 50 degrees C.