On the increasing role of older adolescents and younger adults during the SARS-CoV-2 epidemic in Mexico.

Background: During the first months of the SARS-CoV-2 pandemic, Mexico implemented a national lockdown followed by post-lockdown mitigation. Methods: We used daily number of SARS-CoV-2-confirmed hospitalizations (by date of symptom onset) to assess the changes in the incidence of individuals between the age of 10-59 years during the epidemic in Mexico. For each age group g, we computed the proportion E(g) of individuals in that age group among all cases aged 10-59y during the early lockdown period (April 20-May 3, 2020), and the corresponding proportion L(g) during the late lockdown period (May 18-31, 2020) and post-lockdown mitigation (June 15-28, 2020). For each later period (late lockdown or post-lockdown), we computed the proportion ratios relative to the early lockdown period PR(g)=L(g)/E(g). For each pair of age groups g1,g2, PR(g1)> PR(g2) is interpreted as a relative increase in SARS-CoV-2 infections in the age group g1 compared to g2 for the late lockdown and post-lockdown periods vs. the early lockdown period. Results: For the late lockdown period, the highest PR estimates belong to persons aged 15-19y (PR=1.69(95%CI(1.05, 2.72))) and 20-24y (PR=1.43(1.10,1.86)). For the post-lockdown period, the highest PR estimates were also in age groups 15-19y (PR=2.05(1.30, 3.24)) and 20-24y (PR=1.49(1.15,1.93)). These estimates were higher in persons 15-24y compared to those ≥30y. Conclusions: Our results suggest that adolescents and younger adults had an increased relative incidence during late lockdown and the post-lockdown mitigation periods. The role of these age groups during the epidemic should be considered when implementing future pandemic response efforts.