New vaccine to prevent type-1 polio three times as effective as standard vaccine

Apr 12 2007

The new vaccine to prevent type-1 polio is almost three times as effective as the standard vaccine, according to new research published in The Lancet.

The study found that each dose of the new monovalent oral poliovirus vaccine, known as mOPV1, protected 30% of susceptible children in northern India against paralytic poliomyelitis. The standard trivalent vaccine in the same setting protected just 11% of children per dose.

This is the first published study to confirm the success of mOPV1, a high potency vaccine developed, licensed and introduced to immunisation rounds to combat type 1 polio in India in 2005.

mOPV1 targets type 1 polio, the most prevalent of the three strains of the disease, compared with the trivalent vaccine, which targets types 1, 2 and 3. The efficacy of trivalent vaccines can be diminished because different strains of poliovirus interfere with one another inside the body, sometimes producing immunity to one strain but not another.

Monovalent vaccines do not incur problems with interference between vaccine strains because they include just one of the three strains.

Polio persists in northern India because of poor sanitation and crowded conditions which favour the spread of polio and can also reduce the efficacy of oral poliovirus vaccines. Children in the area often have diarrhoea or other infections that stop the vaccine from working properly.

The researchers found that by the end of 2006 in the states of Uttar Pradesh in India, between 76% and 82% of children aged 0-23 months were estimated to be protected by vaccination against type 1 polio, compared with 59% at the end of 2004, before the introduction of mOPV1.

Dr Nick Grassly, lead author of today's study from the department of Infectious Disease Epidemiology at Imperial College London, said: "Our research shows that the clinical efficacy of the monovalent vaccine in this difficult setting is about three times that of the trivalent vaccine against type 1. This is important, since a child has an 80% chance of protection after 5 doses of this new vaccine. With the trivalent vaccine 14 doses were needed to reach this level of protection.

"The global eradication of type 2 wild poliovirus in 1999, probably due to the greater efficacy of the trivalent vaccine against this type, proves the concept that with a more efficacious vaccine, wild poliovirus can be eradicated," he added.

Today's study shows that providing multiple doses of mOPV1 to children in areas of endemic polio substantially improves the probability of rapidly eliminating the remaining chains of type 1 poliovirus transmission across the world. mOPV1 is a central element of the strategy for interrupting poliovirus transmission.

The researchers reached their conclusions after comparing the vaccination histories of 2076 children with paralytic type 1 polio with the same number of children with paralysis due to causes other than polio, who had a similar date of onset of paralysis, age and district of residence.

Polio is a highly infectious disease that primarily affects children under three years of age. Paralysis develops in a small minority of cases, which is permanent and can be fatal. The Global Polio Eradication Initiative, which started in 1988 and is spearheaded by the World Health Organization (WHO), Rotary International, the US Centers for Disease Control and Prevention (CDC) and UNICEF, has seen endemic polio eradicated everywhere except in parts of India, Pakistan, Afghanistan and Nigeria. Vaccination is a key part of this initiative. When the initiative began it was estimated that polio was paralysing 1,000 children every day, whereas in 2006 this number was approximately five children a day.

This study was supported by a Royal Society Research Fellowship to Dr Grassly.