Minnesota officials link polio infection to oral vaccine

Apr 14, 2009 (CIDRAP News) – Minnesota health officials said today that they are investigating the death last month of a Minnesotan who was infected with a polio virus strain found in the oral polio vaccine (OPV).

The patient likely acquired the vaccine-derived polio virus infection from someone who had received the live-virus OPV, which was discontinued in the United States in 2000, the Minnesota Department of Health (MDH) said in a press release today. The injected polio vaccine contains only inactivated virus.

The patient's symptoms included paralytic polio, but officials said they don't know to what degree the infection contributed to his or her death. The MDH said the patient had a weakened immune system and multiple health problems, but that state law prohibits it from providing further disclosing information about the patient.

Aaron DeVries, MD, MPH, a medical epidemiologist with the MDH, told CIDRAP News that though the investigation is ongoing, sequencing data on the patient's virus samples suggest that he or she may have acquired the virus up to 10 years ago when the OPV vaccine was still administered on a standard schedule. He said officials don't have detailed information about the patient's vaccination status.

Ruth Lynfield, MD, Minnesota's state epidemiologist, said state officials are working with local and national authorities to investigate the case and that no additional cases of polio have been reported so far in connection with the patient.

"It's important to note that while there is no risk to the general public, many people still have vivid memories of a time when polio was a major public health concern before the first vaccines were introduced in the 1950s," she said. "This is a very rare occurrence and does not signal a resurgence of polio."

In rare instances, a person who has been vaccinated with OPV and is shedding the virus in his or her stool can transmit the virus to a person who has never received the polio vaccine or who has certain immune deficiencies. Only 45 cases of vaccine-derived polio disease in patients with immunodeficiencies have been reported in the world since 1961, the MDH said.

In 2005, the US Centers for Disease Control and Prevention (CDC) reported that a 22-year-old US woman contracted vaccine-derived paralytic polio while traveling in Central and South America and was flown to an Arizona hospital for treatment.

The CDC recently reported that in 2008, vaccine-derived polioviruses were detected in patients from eight countries who had acute flaccid paralysis.

The MDH said the recent case is only the second polio infection caused by a vaccine strain in the United States since 2000 when the live-virus vaccine was discontinued. The other similar case also occurred in Minnesota; in 2005 a vaccine-derived polio infection was detected in an unimmunized child from a community that had low immunization levels. The child did not experience neurologic symptoms.

DeVries said there doesn't appear to be a relationship between Minnesota's two cases and that each infection involved a different type of vaccine-derived polio virus.

Lynfield said Minnesota's detection of both of the nation's cases since 2000 might be related to a high level of cooperation between clinicians, a strong clinical laboratory network in the state, and a Public Health Laboratory that looks for rare pathogens such as the polio virus.

Investigators from the MDH are working with hospital staff to assess if any healthcare workers are at risk for the disease, ensuring that their immunizations are up to date, and monitoring their health status.

Only unvaccinated people and those with impaired immune systems who had direct, ungloved contact with the patient's secretions are at risk for polio infection, DeVries said in the press release. "If you don't hear from a public health or healthcare official, you're not at risk," he added.

The case serves as a reminder for people to check if their vaccination status is current, he said. "Make sure you're protected and your children are protected." Those who have had their polio vaccines and are healthy have full immunity to the disease. The series of three polio shots is usually administered during infancy.

Over the past 20 years, world health officials have made great strides toward their goal of eradicating wild polio virus infections. However, the CDC recently reported that the efforts lost some ground in 2008 because of polio's spread to new parts of Nigeria and because political conflict in Afghanistan and Pakistan have hampered the delivery of polio vaccine to children.

The lynchpin of global polio eradication efforts has been the less expensive and easier-to-administer oral vaccine that contains live, attenuated virus that multiplies in the gut, offering passive immunization to other people. However, the vaccine virus sometimes mutates into a virulent type that can cause polio paralysis and spread through shedding to those who aren't vaccinated.

In 2006 and 2007 an outbreak of vaccine-derived polio in Nigeria struck 69 children who had acute flaccid paralysis, according to the CDC.

The last naturally occurring paralytic polio infection occurred in the United States in 1979, the MDH said.

See also:

Feb 3, 2006, MMWR report on imported vaccine-derived polio case

Apr 2 CIDRAP News story "Polio eradication efforts lost ground in 2008"

Oct 16, 2008, CIDRAP News story "Polio vaccination may continue after wild virus fades"

Jun 18, 2008, CIDRAP News story "Coalition declares 'final push' to end polio"

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