Polio in Pakistan, 2023–2024: Few Cases but Widespread Virus in Sewage

Summary

• Wild poliovirus type 1 (WPV1), the only wild strain still circulating, is endemic only in Afghanistan and Pakistan, which share borders and are treated as one epidemiologic block.
• 14 WPV1 cases were reported in Pakistan from January 2023 to June 2024, compared with 21 in January 2022–June 2023. But the virus reemerged widely in its old strongholds — Karachi, Peshawar and Quetta — shown by a spike in positive sewage samples.
• Meeting community demands for basic services and doubling down on reaching children repeatedly missed by vaccination could bring elimination within reach.

Background

Since the Global Polio Eradication Initiative began in 1988, two of the three wild serotypes have been eradicated. Indigenous WPV1 transmission has never been interrupted in Pakistan. The initiative's 2022–2026 plan aimed to end all transmission in 2023, but it continued into 2024. More than 300 WPV1-positive sewage samples in 2023–2024 show Pakistan is not on track, amid a difficult sociopolitical and security situation.

Vaccination

• Routine: in 2023, WHO and UNICEF estimated 86% of children had 3 doses of oral polio vaccine (OPV) and one dose of inactivated vaccine (IPV) by age 1, and 84% two IPV doses (added in 2021). But a 2021 survey found 3-dose OPV coverage from 45.1% in Balochistan to 94.9% in Punjab; no district in Balochistan, Khyber Pakhtunkhwa or Sindh reached 80%, versus 31 of 36 in Punjab.
• Campaigns: in 2023, three national and seven subnational campaigns with bivalent OPV (types 1 and 3); national rounds target 45 million children under 5. Fractional-dose IPV was given in parts of Khyber Pakhtunkhwa and Balochistan. In 2024 so far: two national, two subnational and one outbreak-response campaign.
• Gaps: in south Khyber Pakhtunkhwa, up to 706,613 children were not vaccinated in the January 2024 round because it wasn't safe to run; in Dera Ismail Khan (372,726 children under 5), three of four rounds from November 2023 to April 2024 couldn't be held. Communities boycott campaigns, mostly over unrelated demands like clean water and electricity, and worker safety remains a concern.
• Quality: in the June 2024 campaign, the share of union councils passing quality checks ranged from 82% (Balochistan) to 89% (Punjab), but some districts passed as few as 25% (Loralai) and 37.5% (Killa Abdullah). 599,105 children (3.3%) were missed, including 51,199 refusals.

Surveillance

• Paralysis surveillance: the national non-polio acute flaccid paralysis rate was 20.2 per 100,000 children under 15 in 2023 (provinces 11.6–33.1), far above the benchmark of 2; 17.4 annualized in 2024. Stool adequacy met the 80% target everywhere but Islamabad in 2023 (76.9%). But district-level gaps persist.
• Sewage: 124 sites. Positive for WPV1: 37 of 1,325 (3%) in 2022, 126 of 2,563 (5%) in 2023, and 203 of 942 (22%) in 2024 so far — in Sindh (mostly Karachi), Balochistan, Islamabad, Khyber Pakhtunkhwa and Punjab, about 60% from Karachi, Peshawar and Quetta.

Cases

• 2023: three in Bannu and one in Orakzai (Khyber Pakhtunkhwa), two in Karachi East (Sindh). 2024: six in Balochistan, two in Sindh.
• The 14 children were 9 to 144 months old (median 30 months); seven had never had routine OPV, two had 1–2 doses, five had 3.
• No vaccine-derived type 2 cases since April 23, 2021, after 165 in July 2019–April 2021.
• Genetics: of the 2023 viruses, nine were from the Pakistan-endemic YB3C cluster and 123 from YB3A, co-circulating in eastern Afghanistan; the 2024 cases were YB3A4A (6) and YB3A4B (2). Six "orphan" viruses pointed to surveillance gaps.

Figure 1. Polio cases by month, January 2019–June 2024. Figure from the CDC report.

Figure 2. Wild poliovirus cases by province and period. Figure from the CDC report.

What it means

Transmission spread more widely from the second half of 2023, even as south Khyber Pakhtunkhwa — long a trouble spot — reported no cases in 2024 and YB3C viruses disappeared after November 2023.

• Low case counts, high sewage positivity: likely surveillance gaps below the provincial level, and perhaps IPV — which prevents paralysis but not gut infection and spread — masking circulation. Yet half the children with polio had never had routine OPV, showing immunity gaps.
• Campaign quality still falls short in places; missed children must be tracked and vaccinated, community engagement strengthened in the reservoirs, and campaigns synchronized with Afghanistan.

Limits: parents' recall of vaccination history may be wrong, and finger-marking doesn't always mean a child was actually vaccinated.

Outlook: interrupting transmission by the end of 2024 was unlikely, but Pakistan remains politically committed. Its frontline workers keep risking their safety; meeting demands for clean water and electricity could win cooperation, and with concerted tracking of missed children, eradication could come within reach.

Sources

Based on Chukwuma Mbaeyi, Anwaar ul Haq, Rana Muhammad Safdar and others, "Progress Toward Poliomyelitis Eradication — Pakistan, January 2023–June 2024," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain.