Transmission of poliomyelitis virus; analysis of differing interpretations and concepts, practical implications

Intestinal mucosal immunity is unimportant for polio eradication: the failure of oral polio vaccination

AIMS

To explore if intestinal immunity induced by infection with live viruses in the oral poliovirus vaccine (OPV) is essential, necessary or even helpful in interrupting transmission of wild poliovirus (WPV) for global polio eradication.

METHODS

We reviewed the biology of virus-host interactions in WPV infection and its alterations by OPV-induced immunity for direct evidence of the usefulness of intestinal immunity. We also explored indirect evidence by way of the effect of the inactivated poliovirus vaccine (IPV) on the biology and on transmission dynamics of WPV.

RESULTS

Immunity, systemic and intestinal, induced by infection with WPV or vaccine viruses, does not prevent re-infection with WPV or vaccine viruses respectively, when exposed. Such re-infected hosts shed virus in the throat and in faeces and are sources of further transmission. Immunity protects against polio paralysis-hence reinfection always remain asymptommatic and silent.

CONCLUSION

Vaccine virus-induced intestinal immunity is not necessary for polio eradication. The continued and intensive vaccination efforts using OPV under the assumption of its superiority over IPV have resulted in the well-known undesirable effects, namely vaccine associated paralytic polio and the emergence of de-attenuated circulating vaccine-derived polioviruses, in addition to the delay in completing global WPV eradication.

Investigation of elevated case-fatality rate in poliomyelitis outbreak in Pointe Noire, Republic of Congo, 2010

BACKGROUND

Multiple cases of paralysis, often resulting in death, occurred among young adults during a wild poliovirus (WPV) type 1 outbreak in Pointe Noire, Republic of Congo, in 2010. We conducted an investigation to identify factors associated with fatal outcomes among persons with poliomyelitis in Pointe Noire.

METHODS

Polio cases were defined as acute flaccid paralysis (AFP) cases reported from 7 October to 7 December 2010 with either a stool specimen positive for WPV or clinically classified as polio-compatible. Data were obtained from medical records, hospital databases, AFP case investigation forms and, when possible, via interviews with persons with polio or surrogates using a standard questionnaire.

RESULTS

A total of 369 polio cases occurred in Pointe Noire between 7 October and 7 December 2010. Median age was 22 years for nonsurvivors and 18 years for survivors (P = .01). Small home size, as defined by ≤2 rooms, use of a well for drinking water during a water shortage, and age ≥15 years were risk factors for death in multivariate analysis.

CONCLUSIONS

Consideration should be given during polio risk assessment planning and outbreak response to water/sanitation status and potential susceptibility to polio in older children and adults. Serosurveys to estimate immunity gaps in older age groups in countries at high risk of polio importation might be useful to guide preparedness and response planning.