In London between 1950 and 1968 there were epidemics every two years, but in Liverpool, which had a higher birth rate, there was an annual cycle of epidemics.
Londonis esines aastatel 1950–1968 iga kahe aasta tagant epideemiad, aga Liverpoolis, kus oli sündimus suurem, tekkis epideemia igal aastal.