"In late 1946, an outbreak of influenza occurred in Japan and Korea in American troops. It spread in 1947 to other military bases in the United States, including Fort Monmouth, New Jersey, where the prototype FM-1 strain was isolated. The epidemic was notable because of the initial difficulty in establishing its cause as an influenza A virus because of its considerable antigenic difference from previous influenza A viruses. Indeed, for a time it was identified as "influenza A prime". The 1947 epidemic has been thought of as a mild pandemic because the disease, although globally distributed, caused relatively few deaths. However, as a medical officer at Fort Monmouth, I can personally attest that there was nothing mild about the illness in young recruits in whom signs and symptoms closely matched those of earlier descriptions of influenza. Most remarkable was the total failure of vaccine containing a 1943 H1N1 strain (effective in the 1943–1944 and 1944–1945 seasons) to protect the large number of US military personnel who were vaccinated. Previously, antigenic variation had been noted, but never had it been of a sufficient degree to compromise vaccine-induced immunity (24). Years later, extensive characterization of HA and NA antigens of the 1943 and 1947 viruses and comparison of their nucleotide and amino acid sequences showed marked differences in the viruses isolated in these 2 years; studies in a mouse model also showed that the 1943 vaccine afforded no protection to the 1947 virus challenge (24). Studies in the Fort Monmouth epidemic also documented, by serial bacterial cultures, for the first time the long suspected relationship of influenza to group A streptococcal carriage and disease."