Optimizing oral polio vaccine efficacy

This area of research focuses on optimizing oral polio vaccine efficacy to accelerate polio eradication. It includes evaluating new vaccines and exploring novel uses of existing vaccines to enhance immunity.

Enhancing mucosal immunity in India

In India, persistent transmission of poliovirus is highly localized in a few districts, and high levels of population immunity (>95%) are necessary to stop transmission.

New data have highlighted the importance of understanding mucosal immunity in addition to humoral immunity. Research is looking at ways to both enhance mucosal immunity and also to lower the immunity threshold. Studies are being implemented to:

• investigate the epidemiology and determine the risk factors of decreased mucosal immunity
• evaluate possible interventions to boost mucosal immunity
• assess potential surrogate measures of mucosal immunity against poliovirus.

Known risk factors that contribute to compromised vaccine efficacy include chronic diarrhoea, high enteric disease burden and inadequate sanitation infrastructure. Studies are looking at ways of reducing these risk factors through add-ons such as zinc supplementation, as well as water and sanitation measures.

Zinc supplementation

Given that zinc has been associated with a reduction in diarrhoeal incidence, this research will evaluate whether zinc supplementation increases the efficacy of the oral polio vaccine. It will also investigate whether low zinc status in infants contributes to a diminished immune response to oral polio vaccine.

Water and sanitation measures

This research will evaluate the impact of simple sanitation measures on vaccine efficacy – for example, increasing access to clean water by protecting hand pumps from faecal contamination.

Other ways of reducing risk factors

Other interventions, such as improving nutrition, parasite treatment, and combining oral polio vaccine with inactivated polio vaccine, may also be tested for their impact on vaccine efficacy.

Monovalent oral polio vaccine (mOPV)

Results of clinical trials in Egypt and northern India have confirmed that the efficacy of mOPV1 is superior to trivalent OPV in inducing immunity against poliovirus type 1. These results support the continued widespread use of this vaccine in children to eradicate the last chains of poliovirus type 1 transmission in India.

Bivalent oral polio vaccine (bOPV)

Bivalent oral polio vaccine simultaneously targets the two remaining types of wild poliovirus (type 1 and type 3) and was developed to improve the efficiency and impact of vaccination campaigns in areas where both poliovirus types co-circulate. Results of a multi-centre clinical trial in India have demonstrated that bivalent oral polio vaccine (bOPV) is ‘non-inferior’ to mOPV1 and mOPV3 individually, and ‘superior’ to trivalent oral polio vaccine.

Based on these results the Advisory Committee on Poliomyelitis Eradication (ACPE) recommended that bOPV should be used to complement trivalent OPV in routine immunization and to complement tOPV and mOPVs in supplementary immunization activities. Bivalent oral polio vaccine was first used in Afghanistan in December 2009, when 2.8 million children under five years old received the vaccine.

Sutter R. et al. Immunogenicity of bivalent type 1 and 3 oral vaccine: a randomised, double-blind, controlled trial. Lancet 2010; 376:1682-88