The inactivated poliovirus vaccine and the live-attenuated oral poliovirus vaccine were discovered and developed separately by two men who never quite got along. And for years, the scientific community debated about which vaccine to use.

Now, decades later, a study shows that the two vaccines complement each other well, and the combination could be the key to worldwide eradication of polio in the near future.

One injection of inactivated poliovirus vaccine boosted intestinal immunity and reduced excretion by as much as 75% in children who received multiple doses of oral poliovirus vaccine.

The study, conducted in India, shows that in children who had a history of receiving multiple doses of oral poliovirus vaccine (OPV), one injection of inactivated poliovirus vaccine (IPV), boosted intestinal immunity and reduced excretion of the virus by as much as 75%.

The findings also provide support for use of IPV (or OPV) for boosting intestinal immunity for travelers to and from polio-infected countries, according to the investigators Hamid Jafari, M.D., and associates.

"More than 25 years after the World Health Assembly resolution to eradicate polio myelitis, the answer to the vaccine controversy is apparent," they wrote in Science (2014;345:922-5). "Both vaccines, IPV and OPV, should be used."

Polio is currently endemic in only three countries: Afghanistan, Nigeria, and Pakistan. Since 1988 when the Global Polio Eradication Initiative was launched, the incidence of polio cases has decreased by 99%, according to the World Health Organization (WHO).

"But 99% is not enough in eradication," Dr. Jafari, WHO’s director of polio eradication and research, said at a teleconference. "Our aim is 100%. IPV can help us achieve that 1%."

Studies have shown that administration of IPV after OPV closes the humoral immunity gaps, the investigators wrote, but its effect on intestinal mucosal immunity is less well known.

With the help of WHO officers and field workers, Dr. Jafari and colleagues enrolled roughly 1,000 children from the Moradabad district in Uttar Pradash State in India.

The region was also the main limitation of the study, the authors noted, because the immunogenicity of OPV is low there, and "extrapolation or generalization of these findings to other areas of India or elsewhere must be done with caution," they wrote.

Enrolled children were 6-11 months old, 5 years old, and 10 years old. All children had received several doses of OPV prior to enrollment.

The participants were randomized to receive IPV, bivalent OPV (bOPV, containing poliovirus type 1 and type 3), or no vaccine. After 4 weeks, they all received bOPV, and their poliovirus excretion was measured on days 3, 7, and 14.

When comparing the IPV group with the control group, the poliovirus type 1 excretion decreased by 39% in children aged 6-11 months, by 62% in 5-year-olds, and by 74% in 10-year-olds. For poliovirus type 3, the decreases were 71%, 53%, and 76%, respectively.

bOPV significantly decreased excretion of poliovirus type 1 by 52% and type 3 by 41% in only 10-year-olds.

Also, the 10-year-olds had the highest degree of waning intestinal mucosal immunity, the study showed.

Meanwhile, the effect of IPV in inducing humoral immune response was significantly greater than bOPV.

Four weeks after vaccination, the IPV-induced humoral immune response to poliovirus type 1 was 83% in 6- to 11-month-olds, 98% in 5-year-olds, and 96% in 10-year-olds. That’s compared to 2.9%, 3.1%, and 0%, respectively, in the control group. bOPV also induced a humoral immune response, although milder: 14%, 13%, and 42%, respectively among the age groups. Similar results were observed for poliovirus type 3, the authors reported.

OPV has been used as the primary vaccine to eradicate polio, mainly because it’s cheap, easy to administer, and induces mucosal immunity. But the immunity wanes within 6 months, and several doses of the vaccine are required, which could prove challenging, particularly in conflict zone and hard-to-reach areas.

Meanwhile, IPV is more expensive – around $1 per dose, compared with 15 cents for OPV. Also, its administration could prove challenging because it has to be injected. But WHO officials said that the existing budget and vaccination programs that are already in place should help with successful introduction of IPV in targeted areas.

WHO recommended in 2012 that all countries introduce at least one dose of IPV in their routine immunization program, mainly to reduce the risks associated with the withdrawal of the poliovirus type 2 component of OPV. Poliovirus type 2 was last reported in 1999.

"IPV is the best way to rapidly boost immunity," Dr. Roland Sutter, one of the study’s authors and WHO’s coordinator of research and product development, polio, said at the teleconference.

The findings provide a critical piece of knowledge and can prevent epidemics and international spread of the disease and help "secure a lasting polio-free world," he said.

The study was funded by the Rotary International Polio Plus Program. There were no financial disclosures by the authors.

nmiller@frontlinemedcom.com

On Twitter @naseemmiller

Two polio vaccines are better together