Multiple public health agencies have declared a public health emergency over a potential polio-like illness, but a trace amount of viral DNA that can cause similar symptoms has not been found in vaccine doses or in some laboratory tests. That means so far, the government should not urge parents to stop immunizing their children, at least not yet.
Experts say three health agencies — the Centers for Disease Control and Prevention, the Food and Drug Administration and the National Institutes of Health — don’t know yet what to make of the existence of this microscopic, naturally occurring virus, which resembles the so-called polio virus. Only since last month have scientists been able to test samples taken from CDC laboratories.
“At this point in time, the evidence suggests that the observed outbreak in the Netherlands is the result of a novel infectious poliovirus virus causing an acute respiratory syndrome (ASR) infection, but additional investigation is needed,” the CDC wrote last month in an alert to hospitals and health care providers around the country. As of Wednesday, the alert had not changed, though experts caution that more research and testing still is needed.
Poliovirus has not been spotted in the United States since the disease was formally eradicated in 2000. The federal government plans to take several steps to address the possible outbreak. These include:
— Establishing a task force made up of public health experts and regulators;
— Cloning the virus to confirm its presence and to verify results from laboratory studies;
— Enforcing federal standards for all tested vaccine doses.
But CDC Director Dr. Brenda Fitzgerald also has said that “the initial data would indicate it is not a rare but novel type of virus.” That has raised some caution and skepticism among the public.
“It’s very, very strange,” said Robert Kramer, a vaccine expert at the University of Washington who was involved in the research into the polio vaccine. “It is possible that the discovery in Thailand was also caused by the recent hype about an illness that was likely caused by the new polio virus.” He added, “However, since the CDC report specifically says that the virus’s detection was not linked to recent media reports, they’re on very solid ground.”
Since May, there have been four known cases of ASR. CDC scientists first detected the DNA in testing of more than a thousand samples of feces, saliva and other fluids collected from people infected with ASR in the Netherlands. They also tested 12 imported doses of a polio vaccine donated to Thailand, three packages of donated vaccine sent to Korea and a shipment of seasonal flu vaccines sent to China. The results from the CDC labs on Dec. 8 showed the presence of the virus in three of the 12 vaccine samples. The source was not immediately identified. No virus was found in the Thailand and Korea vaccines. But the CDC reports last month indicated that experts were still searching for specific studies that might explain the virus’s presence.
Experts say the similarity of the ASR and polio viruses is based on common genes. Although the ASR virus is different from the one used to vaccinate against polio, both have been shown to cause “endothelial inflammation,” a tiny clot that sits on the outside of the lungs. Visceral lesions that might be seen on the victim’s respiratory tract have also been identified in ASR cases.
Still, scientists who have studied the ASR virus don’t think it would be that dangerous because it has proven incapable of infecting cells that develop into immune cells. But they say the origin of the virus has still eluded them. They also think the virus may have evolved in order to infect people that haven’t been vaccinated against poliovirus.
Regardless of the current outbreak, states are supposed to keep poliovirus vaccine supplies available to healthcare providers in case there is a new outbreak and questions arise. But the Centers for Disease Control and Prevention plans to designate a health emergency health director to ensure “sufficient stockpile of components and sufficient resources” to respond, should public health officials ever need vaccine doses.