A CONTROLLED CLINICAL TEST OF INFLUENZA A VACCINE

During late January 1941 a small epidemic of influenza occurred among the employees of Grasslands Hospital, one half of whom had been vaccinated with the "complex chick embryo influenza A vaccine" developed by Horsfall and Lennette.¹

Vaccine had been administered to 415 of 826 employees of the institution on December 11 and 12. Scattered cases of influenza appeared several weeks later. The epidemic reached its peak during the seventy-two hours commencing January 31, at which time 32 of the 77 identified cases were reported (chart 1). Of the 77 employees who contracted the disease 32 had been vaccinated and 45 had not. Every patient was examined by us, and whenever possible blood samples were taken during the acute stage of the disease and again during convalescence. No effort was made to recover the virus, one of our purposes being to institute simple and inexpensive procedures which would suffice to