They found that probably the most cost-effective strategy was to protect neonates born in November, 1 month before the RSV season. and developed a mathematical model to compare the effect of different RSV passive immunisation methods (seasonal methods a year-round approach). For each candidate approach, we determined the expected annual proportion of RSV incidence among infants more youthful than 6 months averted (performance) and the percentage of per-dose instances averted between that approach and the year-round approach (relative effectiveness). Findings 39 (75%) of 52 LMICs included in the study had obvious RSV seasonality, defined as having more than 75% of annual SRPIN340 RSV instances happening in 5 or fewer weeks. In these countries with obvious RSV seasonality, the seasonal approach in which monoclonal antibody administration began 3 months before RSV time of year onset was only a median of 16% (IQR 13C18) less effective in averting RSV-associated acute lower respiratory illness (ALRI) hospital admissions than a year-round approach, but was a median of 70% (50C97) more efficient in reducing RSV-associated hospital SRPIN340 admissions per dose. The seasonal approach that delivered maternal vaccination one month before the time of year onset was a median of 27% SRPIN340 (25C33) less effective in averting hospital admissions associated with RSV-ALRI than a year-round approach, but was a median of 126% (87C177) more efficient at averting these hospital admissions per dose. Interpretation In LMICs with obvious RSV seasonality, seasonal approaches to monoclonal antibody and maternal vaccine administration might optimise disease prevention by dose given compared with year-round administration. More data are needed to clarify if seasonal administration of RSV monoclonal antibodies or maternal immunisation is definitely programmatically appropriate and cost effective in LMICs. Funding The Expenses & Melinda Gates Basis, World Health Business. Intro Respiratory syncytial computer virus (RSV) represents a substantial burden of disease in young children (aged 5 years), particularly in low-income and middle-income countries (LMICs) and in babies younger than 6 months.1, 2 RSV activity is seasonal in most parts of the world and thus places substantial pressure on health-care solutions during the seasonal epidemics.3 RSV activity shows a latitudinal gradient in the seasonal onset in each hemisphere; for example, in the northern hemisphere, RSV time of year usually starts in the past due summer months in the tropics and starts in late fall months or early winter months in the temperate RGS20 areas.3, 4 Currently, several RSV vaccine candidates and monoclonal antibodies are in late clinical development.5 Maternal RSV immunisation grants protection to infants passively by improving naturally happening, maternally derived antibodies. New, long-acting monoclonal antibodies SRPIN340 grant safety to babies by directly injecting antibodies designed to have prolonged half-lives (approximately 5 weeks).6 In 2020, a cost-effectiveness study based on hypothetical effectiveness data suggested that both RSV long-acting monoclonal antibodies and maternal vaccination can potentially be optimal candidates for Gavi-eligible countries, depending on a country’s willingness-to-pay ideals.7 Study in context Evidence before this study Respiratory syncytial computer virus (RSV) represents a substantial burden of disease in babies younger than 6 months in low-income and middle-income countries (LMICs). Several novel RSV prophylactic products are being developed to reduce RSV infections SRPIN340 among young babies, including maternal vaccines and immunoprophylaxis. Because these products only provide protection for a number of weeks, RSV seasonality needs to be considered when implementing immunisation programmes to optimise their use. We looked PubMed with no language restrictions for any studies published before May 12, 2020, that assessed the part of RSV seasonality in the performance and effectiveness of novel RSV prophylactic programmes for babies in LMICs using the following search method: (respiratory syncytial computer virus OR RSV) AND (effect OR effective* OR efficien* OR cost-effective*) AND (vaccine OR prophyla* OR antibod* OR immunisation OR immunization). We did not identify any studies that assessed the part of RSV seasonality in the RSV immunisation programmes for LMICs. Added value of this study To our knowledge, this is the 1st study to assess the effect of seasonal versus year-round passive immunisation strategies against RSV for babies in LMICs. In the LMICs with obvious RSV seasonality, seasonal methods prevented nearly as many RSV-associated hospital admissions (performance) and more RSV-associated hospital admissions per dose (relative effectiveness) compared with year-round administration. Results from a multiyear analysis suggested the performance and relative effectiveness of these seasonal methods could remain stable from 12 months to 12 months if countries applied the same seasonal administration schedules. Implications of.