# Variability in the Timing of Respiratory Syncytial Virus Epidemics in Guatemala, 2008–2018

## TL;DR

This study analyzed RSV seasonality in Guatemala from 2008 to 2018, finding significant variability in epidemic timing, which complicates vaccine scheduling.

## Contribution

The study reveals unpredictable RSV epidemic timing in Guatemala, suggesting year-round vaccination is needed for maximal disease prevention.

## Key findings

- RSV epidemic onsets varied by up to 5 months, with both early and late seasonal patterns observed.
- Epidemic thresholds captured 70–99% of annual RSV detections when calculated using past data.
- Onset and offset weeks differed by 2–16 weeks between two surveillance sites in Guatemala.

## Abstract

The description of local seasonality patterns in respiratory syncytial virus (RSV) incidence is important to guide the timing of administration of RSV immunization products.

We characterized RSV seasonality in Guatemala using the moving epidemic method (MEM) with absolute counts of RSV‐associated acute respiratory infections (ARI) from hospital surveillance in Santa Rosa and Quetzaltenango departments of Guatemala.

From Week 17 of 2008 through Week 16 of 2018, 8487 ARI cases tested positive for RSV by rRT‐PCR. Season onsets varied up to 5 months; early seasons starting in late May to early August and finishing in September to November were most common, but late seasons starting in October to November and finishing in March to April were also observed. Both epidemic patterns had similar durations ranging from 4 to 6 months. Epidemic thresholds (the levels of virus activity that signal the onset and end of a seasonal epidemic) calculated prospectively using previous seasons' data captured between 70% and 99% of annual RSV detections. Onset weeks differed by 2–10 weeks, and offset weeks differed by 2–16 weeks between the two surveillance sites.

Variability in the timing of seasonal RSV epidemics in Guatemala demonstrates the difficulty in precisely predicting the timing of seasonal RSV epidemics based on onset weeks from past seasons and suggests that maximal reduction in RSV disease burden would be achieved through year‐round vaccination and immunoprophylaxis administration to at‐risk infants.