Baker N, Stone H O, Webster R G
J Virol. 1973 Jan;11(1):137-40. doi: 10.1128/JVI.11.1.137-140.1973.
"Monospecific" antisera to the "fragile" hemaglutinnis of H0N1 (PR8) and H1N1 (FM1) influenza viruses detected an asymmetrical cross-reaction between these two strains that could not be explained by a common neuraminidase.