A study to evaluate the durability of protection of AREXVY in preventing respiratory syncytial virus (RSV)-associated lower respiratory tract disease (LRTD) hospitalization in adults 60 years of age (YOA) and older

Admitted to hospital with at least one LRTD or ARI International Classification of Diseases, 10th Revision (ICD-10) code during the pre-defined RSV seasons. RSV seasons are defined below: o 2023/2024 season (01 December 2023

31 May 2028)

• Age 60 years or older at ARI/LRTD hospital admission date.
• Minimum of 12 months of continuous KPSC membership (allowing for a 31-day gap) prior to the admission date of the ARI/LRTD hospitalization.
• Have RSV test results by reverse transcription polymerase chain reaction (RT-PCR) from 7 days prior to 2 days after ARI/LRTD hospital admission (inclusive of the admission date) among KPSC medical center areas that provide AREXVY. KPSC medical center areas that provide Pfizer RSV vaccine were not included.

Receipt of an RSV vaccine other than AREXVY or receipt of more than 1 dose of any RSV vaccine prior to the ARI/LRTD hospitalization admission date.

• Receipt of AREXVY <=14 days prior to the ARI/LRTD hospital admission date.
• Receipt of RSV monoclonal antibody prior to the ARI/LRTD hospital admission date based on all available medical records.
• Hospitalization with a positive COVID-19 or influenza RT-PCR test from 7 days prior to 2 days after the ARI/LRTD admission date with an RSV test result. Were excluded hospitalizations that tested positive for COVID-19 or influenza as these are vaccine-preventable causes of ARI and risks of these infections may not be independent of RSV vaccination status given that vaccination behaviours tend to be correlated across vaccines.