Original sentence: In the last two years, England and Wales have seen an increase in the incidence of mumps infections among adolescents and young adults, which health authorities speculate is due to a drop from 92% to 80% in booster shots
Edited sentence: In the last two years, England and Wales have seen an increase in the incidence of mumps infections among adolescents and young adults, which health authorities attribute to a decline in booster shots from 92% to 80%, which they believe is due to the misinformation spread by Wakefield's study