Acute flaccid paralysis surveillance data analysis, Sana’a City, Yemen, 2012-2021: A retrospective descriptive analysis

Background: WHO certified Yemen polio-free in 2009. Outbreaks of circulating Vaccine Derived Polioviruses (cVDPV) threaten the eventual eradication of all polioviruses. In Yemen, two outbreaks of cVDPV type 1 and 2 were reported in 2020 and 2021-2022, respectively. This study aimed to describe trends and characteristics of AFP cases in Sanaa city over the last ten years, from 2012 to 2021. Methods: This cross-sectional study involved retrospective descriptive analysis of surveillance data. All AFP cases reported to the AFP Surveillance System at the Ministry of Public Health and Population between January 2012 and December 2021 were included. Results: During the ten years’ period, a total of 593 cases of AFP were reported in Sana’a City; none of which was confirmed as poliomyelitis. 56% of AFP cases were males, and 60% aged five years or younger. More than half (61%) of cases had received 4 doses or more of OPV. The predominant clinical feature was fever (79%). Paralysis progressed within 3 days of onset in 437 (74%) cases, which was asymmetrical in 202 (34%) cases. The annual incidence of non-polio AFP ranged from 2.6/100,000 to 4.9/100,000 (mean: 3.5/100,000), which met the WHO target. Regarding sample adequacy, we found that in 2017, the sample adequacy fell short of the expected minimal (80%) level, though all districts met the WHO target (>80%) except in At Tahrir District (77%). Conclusions: The AFP surveillance system has improved over the past 10 years in Sana’a city. However, strengthening the two main indicators of AFP surveillance, especially sample adequacy, is recommended. It is advisable to establish a national laboratory that adheres to WHO-recommended procedures for detecting polioviruses in stool samples. Because zero doses were reported among 12% of AFP cases, maintaining high coverage through routine immunization and supporting supplementary immunization activities is crucial to ensure that most children are vaccinated, thereby contributing to the eradication of polio.