Antananarivo – Quality assurance surveyor Anja Mandimbisoa arrives at a random lot numerically selected, throws her pen in the air, and whichever house it is pointing at when it lands is the next on her evaluation list. With their consent, she then sits down with the family to verify whether the children in the household have the mark on their little fingers confirming they have been vaccinated against polio.

“The fact that it is a random selection provides a true picture of immunization coverage at the district level,” explains Mandimbisoa, one of 16 external Lot Quality Assurance Sampling (LQAS) surveyors trained by World Health Organization (WHO) in Analamanga region, Madagascar, to identify any missed children.

As the country concludes its third round of polio vaccinations this year, the response reflects that the job to end polio does not end with the conclusion of a vaccination round. Instead, it is the actions between rounds that make all the difference.

Thanks to comprehensive post-campaign evaluations, Madagascar has managed to improve the effectiveness of the campaign from 63% in the first vaccination round in May 2023 to 86% in the second (July 2023), and to 88% in the third round in September.

This improvement offers hope for the containment of the variant poliovirus outbreak that began in September 2020. Since then, a total of 49 people have been paralysed and 226 samples have tested positive for polio variant type 1 circulation. Uniquely, two of the cases reported in 2023 are adults, aged 32 and 29.

Led by Madagascar’s Ministry of Health, with support from WHO and health partners from the Global Polio Eradication Initiative (GPEI), the most recent national vaccination campaign successfully delivered more than 18 million vaccine doses between 5–8 September 2023. Teams on the ground immunized nearly 19 million people at risk of contracting this debilitating virus, which can cause paralysis and even death in a matter of days.

WHO not only considers quantitative data, but also qualitative indicators. Lot quality assurance sampling (LQAS), a tool that originated in the 1920s as a quality control methodology in the manufacturing sector, is now proving useful in the public health context.

Supplementary immunization activities are key for polio eradication. They are intended to complement, not replace routine immunization, and aim to interrupt circulation of poliovirus by immunizing every child under five years of age with two doses of oral polio vaccine, regardless of previous immunization.  

Regular data monitoring following a vaccination drive can be unreliable. It can, for instance, show high coverage levels in virtually all areas, including those where the virus could be circulating. To address this challenge, WHO introduced digital LQAS in 2009.

This survey method assesses evidence of campaign quality following supplementary immunization activities in pre-defined areas (known as “lots”), using a small sample size. The survey identifies lots with insufficient evidence of high vaccination coverage, based on the results of a sample of 60 children located in six randomly selected lots (settlements, villages, zones, areas, etc). For vaccination coverage to be considered acceptable, at least 57 of the 60 children must have the vaccination mark on the little finger of their left hand.

“The secret is to properly prepare the next round of vaccination as the current one ends, assessing risks, lessons learned, and quickly agreeing on the next vaccine order to halt polio transmission in Madagascar. Key indicators, such as LQAs, are critical to identify the areas we need to focus on so that we can better support the country, technically and financially,” explains Dr Laurent Musango, WHO Representative in Madagascar.

Once the surveyors have completed their work in a district, the results are archived and shared via the electronic Open Data Kit tool, which allows for timely submission of data to the central level.

WHO epidemiologist Dr Yvonne Kabenga, in Madagascar to supervise the activity and observe the results of the latest vaccination round in Analamanga, in central Madagascar, says they realized during the assessment phase that the marking ink was fading very quickly.

“That is either because the quality of the markers was not ideal or because the vaccinators were not marking the children properly. We have noted this for the next round, so we ensure we procure better markers and better instruct the vaccination teams,” she explains.

The independent monitors also support evaluation efforts during the campaign and, using this detailed data, Madagascar has quickly implemented lessons learned from previous vaccination rounds, focusing on key priority areas at risk for further spread of polio.

As a result, the coordination system has been strengthened at central, regional, district and community levels. National health authorities, with WHO support, have also enhanced both environmental and active surveillance to identify potential cases, and WHO is now considering opening new environmental surveillance sites to collect additional wastewater samples in locations where the virus may be circulating.

In addition, teams now identify people eligible for vaccination ahead of the door-to-door campaigns, sensitizing them through briefings and the dissemination of key messages. This work is conducted in collaboration with political, religious and traditional leaders to address misinformation that could lead to refusal of vaccination.

Dr Ndoutabe Modjirom, polio Rapid Response Team Lead at the WHO Regional Office for Africa, confirms that Madagascar must continue its valuable work to "to reach under-immunized children and adults to protect them against all antigens, not only polio, and to avert resurgence in the future”.