Title

Seroprevalence of measles IgG in children 12-59 months of age in Karachi one year after measles vaccine supplementry immunization activity

Date of Award

2010

Document Type

Thesis

Degree Name

Master of Science in Epidemiology & Biostatistics (MSc Epidemiology & Biostats)

Department

Community Health Sciences

Abstract

Background: Measles is a vaccine preventable disease but still a major health problem in Pakistan. Measles vaccine is given routinely in Pakistan at the age of 9 months and 15 months. In order to make progress towards global measles elimination, in 2007 nationwide measles Supplementary Immunization Activity (SIA) was done in Pakistan and 97% of the targeted population was reportedly immunized. Despite the 97% reported coverage rate of S1A, measles outbreaks continued to occur in Pakistan. These outbreaks showed there is a need to evaluate the effectiveness of national SIA campaign by estimating the proportion of measles immune population. Primary Aim: To estimate the seroprevalence of measles IgG in children 12-59 months of age in Karachi one year after supplementary immunization activity. Secondary Aim: To determine the association of measles serologic immunity with the history of measles vaccination reported verbally or verified by vaccination card in children 12-59 months of age in Karachi. Methodology: It was an analytical cross-sectional study in Karachi. Households were randomly selected through multistage cluster sampling technique. 504 eligible children 12-59 months of age from these households were enrolled. Questionnaire was administered to mothers to gather information of child's vaccination status, past history of measles infection and socio-demographic characteristics. Sero prevalence of measles IgG was detected by presence of measles IgG antibodies in oral fluid sample (saliva) collected using Oracol oral specimen collection devices following manufacturer's guidelines. Measles IgG was measured using Microimmune IgG capture ETA kit following manufacturer's instructions. Statistical analysis was done by SAS 9.1 using logistic regression. Results: Measles IgG antibodies were present in 276 (54%) children. The proportion of children who had received a single dose and two doses of measles vaccine were 394 (78%) and 62 (12%) respectively. Among 394 single dose measles vaccine recipients 229 (58%) had serologic immunity. Out of 62 second dose measles vaccine recipients, 40 (64%) had IgG antibodies detected. Non routine dose of measles vaccine delivered through supplementary immunization activity was reported by only 3% of the children. The odds of being measles IgG antibody positive in card verified single dose measles vaccine recipients were 2.67 (95% CI 1.39, 5.10) times the odds of being measles IgG positive in children with no measles vaccination. Conclusion: Our study showed measles serologic immunity was present in only 54% of 12-59 months children and there is a large measles susceptible population of children present in Karachi. Based on these results immediate mass measles vaccination campaigns are recommended to prevent future measles outbreaks in addition to strengthening routine immunization services. These efforts are critical to improve measles control and reduce measles burden in Pakistan.

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