Pakistan Prepares for the Polio High Season

Poliovirus transmission in Pakistan follows a seasonal pattern. It is suppressed in the cooler months and builds from mid-year, peaking in the second half. Preparing for that peak — rather than reacting to it — is one of the programme's central planning tasks.

Why the season exists

Poliovirus spreads by the faecal-oral route, through contaminated water, food and hands. Warmer months bring higher rates of diarrhoeal disease, greater environmental contamination and conditions that favour transmission. The same conditions also reduce how well oral polio vaccine takes, because gut infections interfere with it — so the virus gets a double advantage precisely when it is most active.

What preparation involves

• Campaign timing. National and sub-national rounds are scheduled to raise population immunity before the peak. A round delivered in month eight of the season achieves far less than the same round delivered in month two.
• Risk-based targeting. Districts are prioritised by tier, with the highest-risk union councils receiving more frequent rounds and closer supervision. See high-risk areas.
• Surveillance intensification. Environmental sampling frequency increases, and acute flaccid paralysis surveillance is reinforced so cases are detected and investigated quickly.
• Cold chain readiness. Summer heat is the cold chain's hardest test. Vaccine that has been heat-exposed may be no vaccine at all, so equipment, ice pack capacity and vaccine vial monitor discipline are checked before the season.
• Workforce mobilisation. Recruitment, training and retraining of the hundreds of thousands of frontline workers a national round requires.
• Access negotiation. Securing agreement to operate in districts where campaigns have been constrained — the work that has to happen before the season, because during it there is no time.

Reading the leading indicators

The most useful early signal is environmental surveillance in the pre-season months. A May or June picture showing few positives confined to known reservoirs suggests transmission was suppressed through the low season. Widespread positives across multiple provinces at that point indicate the opposite — and give the programme a window of a few months to act.

See May surveillance results and July results.

Why it matters

Pakistan's worst years have been years in which campaign quality slipped going into the high season. 2019 produced 147 cases after campaigns were disrupted in the spring; 2024 produced 74 after immunity had been eroding for some time.

For parents

The high-season rounds are the ones that matter most. Two drops for every child under five, every round. Call 1166 if no team reaches you.

Related: eradication strategy · surveillance