OBJECTIVES: Respiratory syncytial virus (RSV) infections affect 4–7% of the older adult population yearly. Data on RSV burden in older adults is limited in South-East (SE) Asia. This study assessed RSV public health burden and the impact of adjuvanted RSV prefusion F protein vaccine (RSVPreF3) in adults ≥60 years old in: Indonesia (ID), Malaysia (MY), Philippines (PH), Thailand (TH), and Vietnam (VN).

METHODS: A Markov model with monthly cycles tracked RSV cases in patients with acute respiratory illness (ARI), lower respiratory tract disease (LRTD), upper respiratory tract disease (URTD), and LRTD related pneumonia. Hospitalizations and deaths were adapted to each country, over a three-year time horizon. A single adjuvanted RSV vaccine dose with 30-70% coverage was assumed. Demographic inputs consisted of 2024 United Nations country-specific data, epidemiological data was derived from systematic reviews, while vaccine efficacy data was sourced from ARESVi-006 clinical trial (NCT04886596).

RESULTS: Without vaccination, a total of 15,262,881 RSV ARI cases is expected, distributed as follows: 818,430 cases in MY, 2,067,865 in PH, 2,862,251 in VN, 3,386,608 in TH, and 6,127,727 in ID. Similarly, 7,265,549 RSV LRTD cases, 607,166 LRTD-related hospitalizations, and 57,639 LRTD-related deaths are expected.

Introducing adjuvanted RSVPreF3 with 30-70% coverage could avoid 1,717,793-4,008,185 RSV ARI cases distributed as follows: 88,918-207,476 in MY, 245,857-573,666 in PH, 304,477-710,446 in VN, 372,748-869,746 in TH, and 705,794-1,646,852 in ID. Additionally, between 1,152,040-2,688,095 RSV LRTD cases, 96,273-224,638 LRTD-related hospitalizations, and 9,140-21,326 LRTD-related deaths would be averted.

Numbers needed to vaccinate to prevent one case of ARI/LRTD were 13-14 and 20-21 respectively.

CONCLUSIONS: RSV public health burden in older adults’ population is significant. The introduction of the adjuvanted RSVPreF3 is projected to substantially reduce this burden among elderly in SE Asia. Adjuvanted RSVPreF3 immunization also shows promise to improve public health outcomes mitigating morbidity and mortality associated with RSV infections in this population.