Background
The number of cases of paralytic poliomyelitis has declined in Nigeria since the introduction
of newly licensed monovalent oral poliovirus vaccines and new techniques
of vaccine delivery. Understanding the relative contribution of these vaccines and the
improved coverage to the decline in incident cases is essential for future planning.
Methods
We estimated the field efficacies of monovalent type 1 oral poliovirus vaccine and
trivalent oral poliovirus vaccine, using the reported number of doses received by people
with poliomyelitis and by matched controls as identified in Nigeria’s national surveillance
database, in which 27,379 cases of acute flaccid paralysis were recorded
between 2001 and 2007. Our estimates of vaccine coverage and vaccine-induced immunity
were based on the number of doses received by children listed in the database
who had paralysis that was not caused by poliovirus.
Results
The estimated efficacies per dose of monovalent type 1 oral poliovirus vaccine and
trivalent oral poliovirus vaccine against type 1 paralytic poliomyelitis were 67% (95%
confidence interval [CI], 39 to 82) and 16% (95% CI, 10 to 21), respectively, and the
estimated efficacy per dose of trivalent oral poliovirus vaccine against type 3 paralytic
poliomyelitis was 18% (95% CI, 9 to 26). In the northwestern region of Nigeria,
which reported the majority of cases during the study period, coverage with at least
one dose of vaccine increased from 59 to 78%. Between 2005 and 2007, vaccineinduced
immunity levels among children under the age of 5 years more than doubled,
to 56%.
Conclusions
The higher efficacy of monovalent type 1 oral poliovirus vaccine (four times as effective
as trivalent oral poliovirus vaccine) and the moderate gains in coverage dramatically
increased vaccine-induced immunity against serotype 1 in northern Nigeria.
Further increases in coverage in Nigerian states with infected populations are
required to achieve the levels of vaccine-induced immunity associated with the sustained
elimination achieved in other parts of the country.