Why do hospital admissions spike before winter even starts?

Data from the Brazilian Society of Pediatrics (SBP) analysed nearly 5 million admissions of children under 5 recorded by the public health system (SUS) over 17 years (2008–2025). The finding is clear: the danger window opens in autumn, not winter. Monthly admissions for babies under 1 year rise from an average of 5,619 in February to 16,369 in May — a 191% jump — before winter officially begins.

Which age groups are most affected?

Babies under 1 year are hit hardest and fastest. Children aged 1–4 also see a sharp rise, from 7,194 to 16,419 admissions over the same period (+128%), but the surge for infants is steeper and earlier. The seasonal pattern repeats every year: hospitalisations begin climbing in March, accelerate in April, and peak between May and June.

Why are babies so vulnerable?

"Babies have smaller airways, an immune system still in development, and lower respiratory reserve," explains Marco Aurélio Sáfadi, head of the SBP's Infectology Department. An infection that causes mild symptoms in older children can rapidly lead to breathing difficulties and hospitalisation in an infant. Among babies, acute bronchitis and bronchiolitis account for roughly one-third of cases, tracking closely with Respiratory Syncytial Virus (RSV) — the main cause of bronchiolitis in infants. Importantly, most RSV hospitalisations occur in previously healthy babies, not only premature or chronically ill children.

What warning signs require immediate care?

  • Fast or laboured breathing
  • Nostrils flaring or chest retracting with each breath
  • Persistent fever or high fever in very young babies
  • Difficulty feeding or unusually low activity
  • Bluish tint around the lips or fingernails

What can parents do right now?

"We should not wait for winter to start reinforcing care," says SBP president Edson Liberal. Keep babies away from sick people, maintain good hand hygiene, avoid crowded indoor spaces, and make sure all recommended vaccinations are up to date — starting from the autumn months.

Key Facts:
  • SBP analysed ~5 million SUS admissions of under-5s over 17 years
  • Infant admissions rise 191% from February to May — before winter begins
  • Children aged 1–4 see a 128% increase over the same period
  • RSV is the main cause of bronchiolitis; most victims are previously healthy babies
  • Peak hospitalisation season: May–June; the surge starts in March