With early evaluations of combined immunisation and hygiene programmes showing promising results, more research is needed into what could make a huge difference to health in low- and middle-income countries. Sophie Durrans, Research Uptake Officer at the SHARE Consortium, and Megan Wilson-Jones, Policy Analyst – Health and Hygiene at WaterAid UK, examine the connection.
Water, sanitation and hygiene (WASH) and vaccination are each important tools in the prevention and control of disease, including of common childhood conditions such as diarrhoeal diseases. Long-term, comprehensive disease control and prevention requires safe, clean and adequate water and sanitation infrastructure and sustainable hygiene practices in addition to vaccination programmes; these must exist alongside many other critical factors including disease surveillance and strong health systems that reach everyone.
Compared with injectable vaccines, live oral vaccines can better protect against intestinal infections and are often easier to deliver at scale and to remote communities. However, the effectiveness of oral vaccines differs significantly by region and country. For example, the same rotavirus vaccine that protected 98% of children in the USA and Finland only protected 43% of children in Bangladesh.
This lower effectiveness is often seen in many low- and middle-income contexts, where the burden of vaccine-preventable diseases is highest. The difference in vaccine effectiveness by region is not a new phenomenon – variations have been noted since the early oral polio vaccine trials in the late 1950s.
What does this have to do with WASH?
One factor thought to reduce oral vaccine effectiveness is environmental enteric dysfunction (EED). EED is a syndrome resulting from chronic inflammation of the gut due to repeated bouts of diarrhoea. Recurrent diarrhoea blunts villi in the small intestine, reducing its ability to absorb nutrients and vaccines.
In places with poor sanitation facilities and hygiene practices, vaccine effectiveness can therefore be much lower. This is where water, sanitation and hygiene and vaccination become tightly intertwined, and the rationale for their joint delivery strengthens.
A recent study supported by the SHARE Consortium examined the immunogenicity (the ability of a vaccine to provoke the body to respond) of the rotavirus vaccine in infants with EED in Lusaka, Zambia. Researchers found that in early stages of EED there is damage to the integrity of the intestinal barrier, resulting in increased gut permeability. Pathogens that are normally stopped from passing through are instead absorbed into the body.
In the study, children given the rotavirus vaccination during this stage of EED took up the vaccine and responded very well to it. It’s possible that the later stages of EED are more problematic for absorption. Repeated assaults to the gut from intestinal infections mean that the villi shrink and become blunted. This may lead to malabsorption, the study concludes – infants can’t absorb the vaccine, so might have poor vaccine response and are poorly protected.
However, this is a complex topic that needs more research to strengthen the evidence base. A recent review (in press) exploring the relationship between EED and oral vaccine response concluded that current evidence is insufficient to determine whether EED contributes to oral vaccine underperformance. Fortunately, a number of trials are currently underway – including SHINE in Zimbabwe and SaniVac in Mozambique – and we hope that these results will further our understanding of the role that WASH plays in oral vaccine effectiveness.
Immunisation as an entry point for WASH
The possible relationship between water, sanitation and hygiene and vaccine response further highlights the critical importance of ensuring a comprehensive approach to disease control. Because immunisation reaches more children than does any other health intervention, it also serves as an important entry point at which to integrate WASH interventions.
WaterAid, in partnership with national governments, is piloting an approach in several countries, including Nepal and Mozambique, integrating hygiene promotion into the delivery of rotavirus or oral cholera vaccines.
Results from the Nepal pilot showed that the intervention: improved all key hygiene behaviours from 2% at baseline to 53% a year after implementation; increased immunisation coverage; and reduced drop-out and vaccine wastage rate. Although not measured through a randomised controlled trial design, the independent evaluation observed a substantial reduction in diarrhoea prevalence following the programme. This may be possibly due to improved behaviours including other ongoing programming.
Bringing the two interventions of immunisation and WASH together has the potential to not only strengthen immunisation systems and increase the number of people taking up vaccines, but also to be the missing link in improving the effectiveness of oral vaccines in low- and middle-income settings. We need more research to better understand these biological interactions and more operational experience to explore how to better link WASH and immunisation to maximise health impact.