As part of efforts to rid the world of polio, the World Health Organization recently declared 37 Pacific Rim nations free of the crippling disease. Meanwhile a new report about a small risk from the live virus vaccine is likely to stir some controversy in the developed world.
There are two types of polio vaccine produced today. One, the oldest, uses a weakened form of the live polio virus. Children are exposed to the weakened virus and develop an immune response so when they are exposed to the full strength virus later on in life their bodies can take care of it.
Because the live virus vaccine can occasionally cause polio itself, a dead virus vaccine version is also available and now frequently given to children in nations where there are no active cases of polio reported. The drawbacks of the dead virus vaccine are that it tends to be more expensive and somewhat less effective than the live virus version.
The study published in the Lancet reports that not only can the polio virus end up living inside the gut of children who receive the live virus vaccine, but that it can be found in small amounts in the sewage system Researchers in Japan were able to find detectable levels of polio virus in the sewage system due to the live virus vaccine.
While the researchers concluded that “there is an environmental risk of vaccine-associated paralytic poliomyelitis as long as live oral poliovirus vaccine is not replaced with inactivated polio vaccine,” spokespersons for the World Health Organization pointed out that there has never been a single recorded case of polio being transmitted in this way and the polio virus transmitted to water or sewage this way seems to have an extremely short life span.
“In Cuba,” Dr. Bruce Aylward, who heads up the Western Pacific polio eradication effort, told the BBC, “they found a similar thing was happening, but that the presence of the virus died away naturally shortly afterwards. We have never seen an outbreak caused by this in 30 years.”
A much bigger concern than some extremely small risk of polio transmission from infested sewage is the very real fear that people in developed countries might seize upon this result as a reason to stop having their children vaccinated for polio. In Great Britain and other parts of Europe, anti-vaccination fears are relatively widespread. In some parts of Europe parents are foregoing vaccination in favor of relatively unsafe subclinical exposures (i.e. exposing healthy, uninfected children to other children who have contracted a disease such as the measles).
Unfortunately as long as the disease is present anywhere in the world, children who forego polio vaccinations will face a serious risk of severe health problems should they ever come in contact with the virus.
Polio milestone passed. The BBC, October 29, 2000.