Vaccination coverage survey versus administrative data in the assessment of mass yellow fever immunization in internally displaced persons—Liberia, 2004

Vaccine-preventable diseases in humanitarian emergencies among refugee and internally-displaced populations

“…In 2004, 2 yellow fever mass vaccination campaigns were launched in IDP camps and surrounding communities in Liberia after reports of 4 lab-confirmed cases. 33 Due to the 14 years of civil war, much of Liberia's healthcare infrastructure, public health disease surveillance, and immunization programs were severely disrupted. Survey assessment of vaccination coverage reported 90% by selfreport and 80% by proof of vaccination card.…”

“…The success of the mass vaccination efforts among IDPs required intensive social mobilization, efficient logistical networks, well-trained health staff, and safe vaccine delivery. 33 During a time Liberian and Sierra Leonean refugees and IDPs were in Guinea, a yellow fever outbreak was reported with 688 cases and 225 deaths (CFR 33%) in 2000. 34 Movement through the forested areas of Guinea where yellow fever is endemic into densely-populated camps and urban areas may have led to increased transmission.…”

“…The OCV campaigns were completed through fixed outreach posts and mobile door-to-door teams targeting individuals >1 year of age, excluding pregnant women. 31,33 Distribution of vaccination cards were used to track immunization status, and soap as an incentive to receive the second OCV dose. 31,32 However, despite the success of campaigns, there were security, logistical, and financial challenges related to the 2 dose administration schedule as well as weakened cold chain capacity due to the ongoing conflict.…”

Use of Lot Quality Assurance Sampling (LQAS) to estimate vaccination coverage helps guide future vaccination efforts

“…This method can provide information on coverage by geographic area if the population of subareas is available and the origin of the children vaccinated is known. If population figures are inaccurate, this method leads to either an overestimate (Zuber et al, 2003) or underestimate (Huhn et al, 2006). Overestimation can result in part of the population remaining at risk of the disease; underestimation may result in the organisation of unnecessary public health measures, such as follow-up vaccination campaigns.…”

Use and abuse of rapid mnitoring to assess coverage during mass vaccination campaigns

“…dividing the number of individual vaccine doses administered by the target population) is notoriously unreliable, with estimates commonly reaching > 100%. 3,4 Incomplete tallying or reporting of the number of doses administered can bias the results, as can poorly documented shifts in population, reliance on outdated census data and vaccination of individuals outside the targeted age group or geographic area. Probability-based surveys avoid these problems.…”