British and Indian researchers said the inactivated polio vaccine
(IPV), which is given by injection, could provide better and longer
lasting protection if given alongside the more commonly used live
oral polio vaccine (OPV).
Serious polio outbreaks in Asia, Africa and Europe over the last 10
years have hampered efforts to wipe out the disease, caused by a
virus that replicates in the gut and can be passed on through
contact with infected faeces.
Polio invades the nervous system and can cause irreversible
paralysis within hours - and the World Health Organization's
repeated warning is that as long as any child remains infected with
polio, children everywhere are at risk.
Most vaccination campaigns - including emergency ones that were
started last year covering 20 million children in Syria and
neighboring countries - use multiple doses of OPV to boost immunity
among those at risk.
"Because IPV is injected into the arm, rather than taken orally,
it's been assumed it doesn't provide much protection in the gut and
so would be less effective at preventing faecal transmission than
OPV," said Jacob John, an associate professor at the India's
Christian Medical College, who led the study.
But his team's research, which covered 450 children from a densely
populated urban area in Vellore, India, found that where they
already had a level of immunity due to OPV, the injected vaccine
actually boosted their gut immunity.
"It looks as if the strongest immunity can been achieved through a
combination of the two," he said.
Polio re-emerged in Syria in 2013 for the first time in 14 years,
fanning fears of a wider international spread and prompting a vast
regional emergency vaccination campaign.
Children in unsanitary conditions are particularly vulnerable to
infection with the polio virus, which can spread through
contaminated food and water.
Although transmission of indigenous polio has been declining
substantially in endemic areas since 2012, around 10 countries are
currently considered to have active polio transmission.
Polio is still endemic in three of these - Afghanistan, Pakistan and
Nigeria - and the remainder are countries that were once polio-free
but have been re-infected.
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The Indian children involved in the study, by John's team working
with researchers at Imperial College London, had all received OPV
during standard vaccination programs.
Half of the children were given a dose of the injected IPV vaccine
and half given nothing, and a month later, the children were given a
"challenge" dose of the live oral vaccine to simulate reinfection.
Their stools were tested after a week to see if the polio virus was
present, specifically the two remaining types which have not yet
been eradicated - serotype 1 and serotype 3.
In the children who had received IPV, 38 percent fewer had serotype
1 in their stool and 70 percent fewer had serotype 3, compared to
those who had not been given IPV, according to the study results
published in The Lancet medical journal.
"An additional dose of the injected vaccine is more effective at
boosting immunity against infection than the oral vaccine alone,"
says Nick Grassly, a professor of vaccine epidemiology at Imperial.
"This implies that the IPV could be used to boost immunity in people
travelling from or to polio-infected countries, such as Afghanistan,
Pakistan and Nigeria. It could also replace some of the OPV doses in
immunization campaigns to boost gut immunity, particularly in areas
of poor sanitation."
(Reporting by Kate Kelland; Editing by Andrew Heavens)
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