State health official calls polio case extremely rare

For the second time in four years, health officials have discovered a rare case of polio infection in a Minnesota patient with a severely weakened immune system.

The patient, who died in March, was infected with a live virus found in the oral polio vaccine, said Dr. Aaron DeVries of the Minnesota Department of Health.

DeVries called it extremely rare and said there is no danger to the public.

He said it's not certain whether polio played a role in the death, because the patient had multiple health problems.

The oral vaccine, which contains a live virus, has not been used in this country since 2000.

Polio was virtually wiped out in the United States 30 years ago. But since 1961, the oral vaccine has been linked to nearly four dozen cases of polio, worldwide, in people with immune deficiencies.

In 2005, Minnesota health officials discovered that five unvaccinated Amish children from central Minnesota were infected with the polio virus, including a baby with a weakened immune system. Investigators said that the baby, who was especially vulnerable, probably contracted the virus from someone who had been vaccinated with the live virus.

These are the only cases of vaccine-related polio infection reported in the United States since 2000, the Health Department said.

DeVries said the latest patient, an adult, probably was infected more than 10 years ago but didn't develop symptoms until recently.

Scientists were able to trace the source, using DNA technology, to a strain that was used in an oral vaccine before 2000. Since then, only polio vaccines made with killed viruses, which cannot cause infection, have been used in the United States

The oral vaccine was safe for most people, DeVries said, but the live virus can remain in their system for several weeks, and in rare cases infect another person with a compromised immune system. That's apparently what happened with this patient, he said.

DeVries declined to reveal details about the case, saying "we're doing our utmost to protect the confidentiality of the patient."