http://id.medscape.com/reuters/prof/2001/10/10.15/20011012epid003.html

 

Three Vaccine-Derived Polio Cases Reported in Philippines

ATLANTA (Reuters Health) Oct 12 - Between March and July, three cases of acute flaccid paralysis (AFP) associated with circulating vaccine-derived poliovirus isolates were reported in the Philippines, according to the US Centers for Disease Control and Prevention.

Two of the three case-patients, an 8- and a 3-year-old, received three doses of oral polio vaccine (OPV). The third child, age 14 months, received two OPV doses, CDC researchers report in the October 12th issue of the Morbidity and Mortality Weekly Report.

All three polioviruses were identified as being from Sabin vaccine strain type 1, "with a 3% genetic sequence difference between Sabin 1 vaccine and vaccine-derived poliovirus isolates."

"The three polioviruses are not identical but are closely related (>99% sequence homology," the CDC researchers note. "They also appear to share an identical recombination site with a nonpolio enterovirus in the noncapsid region of the genome."

According to Dr. Roland Sutter of the CDC's National Immunization Program, two rare events took place simultaneously to result in these instances of AFP, which he said is only the second episode of such an outbreak. A similar episode occurred in Haiti from 2000 to 2001.

The first event occurs after about one in every one million doses of OPV administered, Dr. Sutter told Reuters Health. "The live attenuated polioviruses contained in OPV can revert to neurovirulence and cause the paralytic disease they are designed to prevent," he said.

Even less frequently, Dr. Sutter explained, attenuated polioviruses can acquire the transmission characteristics of wild polioviruses. This is only the third time in history that this has happened, he said.

"We believe that to acquire these two characteristics, live attenuated poliovirus probably must circulate in an area with very low vaccination coverage for some time," Dr. Sutter said.

According to the report, OPV coverage did not extend to the three areas reporting the cases: northern Mindanao island (500 miles south of Manila), Luzon island (60 miles south of Manila) and Cavite province (25 miles southwest of Manila).

In response to these cases, the Philippines Department of Health is enhancing surveillance of AFP cases, conducting virologic investigations of aseptic meningitis at major health-care facilities, and assessing polio vaccination coverage in the three communities. In addition, a large-scale mass vaccination campaign with OPV is planned.

"It is too early to know whether there will be additional cases," Dr. Sutter said, "but it is prudent to anticipate and plan for them."

"The Department of Health, the World Health Organization and the CDC are doing everything possible to interrupt transmission of the circulating vaccine-derived poliovirus isolates in the Philippines as quickly as possible," he said.

MMWR Morb Mortal Wkly Rep 2001;50: 874-875.

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