Several low-and middle-income countries, especially in
Africa, need more effective child vaccination strategies to eliminate the
threat from vaccine-preventable diseases, according to a study led by
researchers at the University of Southampton.
Geographers from the University’s WorldPop group found
diphtheria, tetanus and whooping cough (pertussis) vaccination levels in
Nigeria, Democratic Republic of the Congo (DRC), Ethiopia, Mozambique and also
in Cambodia, southeast Asia, fall short of the 80% threshold recommended by the
World Health Organization (WHO). This means the potential for disease
circulation and outbreak in these countries remains high.
Findings are published in the journal Nature Communications.
Using data from Demographic and Health Surveys (DHS) conducted between 2011 and
2016, the researchers examined the performance of routine immunisation (RI)
through the delivery of the three doses of diphtheria-tetanus-pertussis
(DTP1-3) to children aged five and under, including drop-out rates between
doses. They compared this with the delivery of the measles-containing vaccine
(MCV), for which additional supplementary immunisation activities (SIAs) are
often undertaken. Highly detailed (one km sq.) maps showing levels of vaccine
coverage for each country and reflecting the relative performance of routine
and supplementary activities were produced.
The data indicate gaps in the delivery of the first dose of
the DTP vaccine, particularly in DRC, Nigeria and Ethiopia – suggesting poor
access to routine immunisation. However, where routine delivery of the measles
vaccine in the same countries was supported with recurrent SIA campaigns, rates
of coverage were substantially higher. In contrast, Mozambique and Cambodia had
fewer campaigns and saw no real improvement – although both countries had
stronger routine delivery systems.
These results suggest that additional targeted campaigns can make a big
difference to immunisation service delivery, especially in areas with poor
routine immunisation coverage. Lead researcher Dr Chigozie Edson Utazi comments:
“Many things can lead to low vaccination levels, such as poor access to health
services, poor education, low stocks of vaccines and even vaccine refusal. We
have shown that supplementary activities, as a short-term approach, can help
address some of these problems, boost immunisation and improve disease
“The success of any vaccine delivery strategy lies not only with a good
geographical spread, but also in ensuring coverage level among the population
is high enough to stop the spread of the disease. We hope our fine spatial
scale and regional maps will help countries to understand in greater detail
where coverage is low and decide what further interventions are needed in
specific areas to work towards disease elimination.”
The researchers now hope to build on their work by extending to other countries
and conducting further studies which incorporate data on treatment-seeking
behaviour, travel time to health facilities and mobile phone network coverage.
It is hoped that this could lead to the design and implementation of tailored
vaccination delivery programmes.
Reference: Utazi CE, et al. Mapping vaccination coverage to
explore the effects of delivery mechanisms and inform vaccination strategies.
Nature Communications. Published 9 April 2019. https://www.nature.com/articles/s41467-019-09611-1