Back in the old days we used to do long term vaccine controlled studies. Cursory Google search finds: > A long-term follow-up study on the efficacy of further

Back in the old days we used to do long term vaccine controlled studies. Cursory Google search finds: > A long-term follow-up study on the efficacy of further attenuated live measles vaccine, Biken CAM vaccine, S Isomura & all, 1986 > Antibody persistence was measured in 39 children in an open community 12-13 years after immunization against measles with further attenuated live vaccine, Biken CAM. [...] For evaluation of the protective efficacy of the vaccine, matched controls were studied during the same period. Serological examination revealed that 97.5% of the controls were infected with measles and contracted the disease. https://pubmed.ncbi.nlm.nih.gov/3778422/ https://pubmed.ncbi.nlm.nih.gov/3778422/