In 1942 Hirst and his associates1 of the International Health Division, Rockefeller Foundation, developed a new method of concentrating influenza vaccine from allantoic fluid infected with virus. When allantoic fluid from 13 day old infected chick embryos is frozen and thawed, a fluffy white precipitate appears. From 90 to 95 per cent of the virus is usually carried down in this precipitate. The precipitate goes back into solution when the fluid is warmed to 37 C.
While the temperature was kept at approximately 0 C. the precipitate from a large volume of infected allantoic fluid was removed by centrifugation and resuspended in one tenth the original volume of supernatant fluid. The resulting tenfold virus concentrate was then devitalized by the addition of 0.4 per cent formaldehyde solution. Equal volumes of type A and type B concentrate thus prepared were mixed and thoroughly homogenized. The homogenized mixture was distributed in
CONCENTRATED INFLUENZA VACCINE. JAMA. 1945;127(4):221–222. doi:10.1001/jama.1945.02860040031010
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