Use of the moving epidemic method to guide the launch of palivizumab immunization campaigns for respiratory syncytial virus in Québec, Canada.

Objective: The COVID-19 pandemic disrupted the seasonal transmission pattern of respiratory syncytial virus (RSV), challenging the launch of palivizumab immunization campaigns. This study explored the performance of the moving epidemic method (MEM) to guide the launch of such campaigns.

Methods: Data were collected through a continuous RSV surveillance system (07/2013‒03/2022) in Québec, Canada. Two strategies were compared: (1) a "preestablished" approach according to which each annual campaign began on November 1 and ended upon the earliest week with an RSV positivity rate ≤ 10% after March 31; and (2) MEM, according to which each annual campaign began and ended upon meeting an epidemic threshold of RSV positivity. We estimated the proportion of RSV cases that would be covered depending on the approach used for each RSV epidemic.

Results: From seasons 2013-2014 through 2019-2020, RSV cases peaked between weeks 1 and 8, and all epidemic curves overlapped with an intraclass correlation coefficient (ICC) of 0.83. From 2013-2014 through 2019-2020, the epidemic periods determined by MEM and the preestablished approach covered similar proportions of RSV cases (MEM = 91.6%, preestablished = 90.7%) and had a similar duration (MEM = 21.3 weeks, preestablished = 21.7 weeks). With MEM, the 2021-2022 epidemic period started at week 29 and ended at week 51, covering 95.7% of cases. With the preestablished approach, the epidemic period started at week 44 and ended at week 8, covering 28.3% of cases.

Conclusion: During normal RSV seasons, MEM is an effective alternative to the preestablished approach. However, MEM appears significantly more robust to disruptions of RSV's seasonal pattern.