Using both live and inactivated polio vaccines could help speed
the global eradication of polio, a new study reports.
The study, done in Indian children already given the live polio
vaccine, shows that a single dose of the inactivated vaccine boosts
immunity more effectively than an additional live vaccine dose.
The results have already contributed to a decision by World
Health Organisation (WHO) advisers to use the inactivated vaccine
more widely in the push to eradicate polio.
In certain parts of the globe, like Pakistan and Nigeria, polio
is proving difficult to eradicate. Making the choice between an
oral live attenuated vaccine (OPV) and an injected inactivated
vaccine (IPV) has been highly controversial.
To date, OPV has been more widely used because it is cheaper,
requires no needles to administer, and is better able to induce
immunity in the intestinal lining, known as mucosal immunity.
However, the immune response to OPV is highly variable and mucosal
immunity appears to diminish rapidly after OPV, meaning that
several doses of this vaccine may be required, a difficult feat in
remote or conflict zones.
Professor Nick Grassly from Imperial College London said: "The
decision to use inactivated poliovirus vaccine was previously
controversial because it was unclear whether it would improve
intestinal immunity. But in the last year we've published two
studies that have provided convincing evidence that when given to
children who previously received oral vaccine, the inactivated
vaccine offers a very effective boost.
"This means that both OPV and IPV have an important role to play
in the eradication programme. The results have already fed into the
WHO's eradication strategy, and campaigns with the vaccine have
started in Nigeria and are planned for Pakistan, two countries with
persistent poliovirus transmission."
Researchers led by the WHO tested whether use of OPV or IPV
would improve mucosal immunity. They conducted a randomised
clinical trial in northern India in which almost 1,000 infants and
children were given one vaccine or the other.
After four weeks, all the participants were given a "challenge"
with the live-attenuated OPV to test whether they were protected
against infection. In those who had received IPV, the amount of
virus shed in stools after OPV was greatly reduced, meaning these
children were less infectious to others. The IPV group also
produced more antibodies, meaning these individuals are better
protected against polio disease.
The paper, Efficacy of
Inactivated Poliovirus Vaccine in India, is published inScience.