The paper says that the 1977 H1N1 is not identical to the 1950's strains, but very similar, and that a tree build from sequences suggests the 1977 strain is mos

The paper says that the 1977 H1N1 is not identical to the 1950's strains, but very similar, and that a tree build from sequences suggests the 1977 strain is most closely related to the 1950's strains. So there are differences, and the question is, are they natural or synthetic. I do not think the technology was available to make synthetic changes.