Upvote:4
The bishops of Mexico suspended public worship in all of Mexico beginning July 31, 1926, during the Cristero war.
Also, commenting on 1917 Code's Canon 1245 ยง2 (cf. 1983 can. 1245), canonist Dom Charles Augustine, O.S.B., cites Benedict XIV's Constitution Libentissime, which permitted dispensation from Lenten fasting due to a diocese-wide influenza outbreak. Dispensation from Sunday obligation could be done for similar reasons.