Saturday, 24 May 2014

Sichuan polio cases show need for better vaccine coverage

by Michael Woodhead
A small outbreak of polio that occurred in Sichuan was derived from a vaccine-related strain, according to researchers from the WHO Regional Polio Reference Laboratory in Beijing.
In a new report they describe the strains of polio virus isolated from three cases of flaccid paralysis that occurred in an isolated region of Aba, Sichuan in 2011 and 2012.  They say the virus strain was similar to that used in the trivalent (Sabin) oral polio vaccine, but with minor changes that affected its attenuation and temperature sensitivity. The virus was found in the three cases of polio, all of which occurred in unimmunised infants below the age of one. The virus was also found in one close contact. The new strain of polio virus appears to have been circulating in the remote community for about seven months, they said."
"Our findings reinforce the point that circulating vaccine-derived poliovirus can emerge and spread in isolated communities with immunity gaps, and highlight the emergence risks of type 2 circulating vaccine-derived poliovirus accompanying the trivalent OPV used, they said.
"To solve this issue, it is recommended that type 2 OPV should be removed from the trivalent OPV or use of inactivated polio vaccine (IPV) instead.
The findings are reported in Clinical and Vaccine Immunology.

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