[Evaluation of the lifetime of nail markings during polio vaccinations in Chad].
BACKGROUND
SID (Supplemental Immunization Days) is a special strategy intended to accelerate eradication of poliomyelitis in countries where it is still endemic (India, Afghanistan, and Pakistan in Asia, and Nigeria in Africa). This strategy is also applied in Nigeria's neighbours (Cameroon, Chad, Niger and Benin). Since the poliomyelitis virus was imported from Nigeria in 2001, Chad has reported cases of poliomyelitis every year. After 30 SIDs in Chad and the inaccurate or false attribution of side-effects to polio vaccines, some groups persistently refuse polio vaccination. To ascertain the true coverage of SID, the Ministry of Health and several partners (WHO, UNICEF and Rotary) conduct external coverage evaluations, to identify the under-vaccinated areas where population may be refusing immunization. The nails of the children receiving vaccinations are marked with indelible ink and those markings are the best indicator of the area's actual SID coverage. When coverage investigators arrive and propose vaccination to all children not immunized during SID, mothers who wish to refuse vaccination may claim that the children's markings disappeared after a few days, due to bathing. WHO experts have found that markings applied to their own nails with the WHO-recommended markers persist a few weeks, but others suggested that the markings may disappear much faster among children living in a traditional tropical environment. Until now, the lifetime of these markings has not been tested among children in Africa.


OBJECTIVE
To determine the lifetime of the fingernail markings after SID and factors that influence this lifetime in children young than 5 years old in Chad.


METHODS
This prospective cohort study of 200 children (aged 0 to 59 months) took place from March to May 2009 in Milezi, a health zone north of Ndjamena, the capital of Chad, in central Africa. These children received nail markings on their left little finger with an indelible marker pen provided by WHO. The finger was monitored for 35 days, visually and by photographs, to determine the factors associated with the lifetime of the markings. Kaplan-Meier and log-rank methods were applied to estimate their survival curve and the variables significant for their lifetime; the Cox proportional hazard model was used to determine multivariable-adjusted hazard ratios.


RESULTS
Of the 184 children surveyed through the end of the study, the markings disappeared after 35 days of follow-up for 35% of them. The average lifetime of markings on these children was 28 days (SD: 4.95) and was associated, according to the Cox model, with 3 variables: the quality of the marking (RR = 0.335, 95% CI: 0.182-0.617, p < 0.001), playing with soil or mud (RR = 0.38, 95% CI: 0.208-0.697, p = 0.002), and living in different blocks, after stratification for the variable of application of chemical products on the nail. The latter could not be included in the Cox model because it made the markings disappear instantly.


CONCLUSIONS
WHO experts were right in stating that the lifetime of the markings was sufficient to estimate coverage accurately when external evaluation takes place one or two weeks after SID. The only action found to make markings disappear rapidly was the application of chemical products. Mothers who tell SID attendance evaluation teams that the marking disappeared with bathing are expressing a tacit refusal of vaccination. These evaluations, which take place well before the disappearance of markings, help to determine the precise coverage of SID.
Oxford University Clinical Research Unit 195, rue Ham-Tu District 5 Ho-Chi-Minh Ville Vietnam. cuonghq@ocucru.org
Huong
H
Quoc Cuong
Martin
M
Schlumberger
Salomon
S
Garba Tchang
Dah
D
Ould Cheikh
Marianne
M
Savès
Barah
B
Mallah
Jacques
J
Demtilo Attilo
Ndeikoundam
N
Ngangro Mosurel
Youssouf
Y
Gamatié
D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007281:Ink; D009262:Nails; D023321:Poliovirus Vaccines / Q000008:administration & dosage; D011159:Population Surveillance / Q000379:methods; D011446:Prospective Studies; D013997:Time Factors; D014611:Vaccination / Q000706:statistics & numerical data*
D023321:Poliovirus Vaccines