The effect of immunization on measles incidence in the Democratic Republic of Congo Results from a model of surveillance data

Thursday, 29th of October 2015

Doshi RH¹ Shidi C² Mulumba A³ Eckhoff P⁴ Nguyen C⁵ Hoff NA⁶ Gerber S⁷ Okitolonda E⁸ Ilunga BK⁹ Rimoin AW¹⁰.

Abstract

BACKGROUND

Measles continues to be a leading cause of vaccine-preventable disease mortality among children under five despite a safe and efficacious vaccine being readily available. While global vaccination coverage has improved tremendously measles outbreaks persist throughout sub-Saharan Africa. Since 2010 the Democratic Republic of Congo (DRC) has seen a resurgence of measles outbreaks affecting all 11 provinces. These outbreaks are mainly attributed to gaps in routine immunization (RI) coverage compounded with missed supplementary immunization activities (SIAs). We utilized national passive surveillance data from DRCs Integrated Disease Surveillance and Response (IDSR) system to estimate the effect of immunization on measles incidence in DRC.

METHODS

We investigated the decline in measles incidence post-immunization with one dose of measles containing vaccine (MCV1) with and without the addition of supplementary immunization activities (SIAs) and outbreak response immunization (ORI) campaigns. Measles case counts by health zone were obtained from the IDSR system between January 1 2010 and December 31 2013. The impact of measles immunization was modeled using a random effects multi-level model for count data with RI coverage levels and mass campaign activities from one year prior.

RESULTS

The presence of an SIA (aIRR [95% CI] 0.86 [0.60-1.25]) and ORI (0.28 [0.20-0.39]) in the year prior were both associated with a decrease in measles incidence. When interaction terms were included our results suggested that the high levels of MCV1 reported in the year prior and the presence of either mass campaign was associated with a decrease in measles incidence.

CONCLUSIONS

Our results highlight the importance of a two-dose measles vaccine schedule and the need for a strong routine immunization program coupled with frequent SIAs. Repeated occurrences of large-scale outbreaks in DRC suggest that vaccination coverage rates are grossly overestimated and signify the importance of the evaluation and modification of measles prevention and control strategies.