Complex sentence: Since the MMR vaccine was added to the mandated childhood immunization schedule in 1980, according to Rollens, California has experienced an increasing epidemic of autism, while 14 additional doses of vaccines have been added to the state's mandated childhood immunization schedule.
Split into simpler sentences: Since the MMR vaccine was added to the mandated childhood immunization schedule in 1980, according to Rollens, California has experienced an increasing epidemic of autism. Since then, 14 additional vaccine doses have been added to the state's mandated childhood immunization schedule.