Low immunization rates in parts of U.S. could pave way for polio outbreak




July 15, 2010 - Michael Brady, M.D., FAAP



A recent polio outbreak in Tajikistan shows how precarious our control of the disease can be when immunization rates fall below the World Health Organization target level of 90%. The polio immunization rate in Tajikistan is 87%.


This is the first persistent polio outbreak in a certified polio-free country, with more than 560 cases of flaccid paralysis reported.


Cases also are appearing in Russia and Uzbekistan. It appears that asymptomatic polio-infected individuals were responsible for transmission out of Tajikistan. The occurrence of polio in Tajikistan[,] and spread within the region[,] documents that global travel can result in polio occurring anywhere in the world where immunization rates are inadequate.


In the United States, we are comforted by the fact that the Western Hemisphere was certified polio-free in the early 1990s. Since that time, there have been occasional imported cases with no evidence of further transmission. However, polio immunization rates are lower than 90% in many areas of the United States due to a lack of concern with polio due to no recent experience in the United States, concerns about vaccine safety, religious objections to immunization and anti-vaccine activities. With increasing globalization, the United States could be just an asymptomatic traveler away from an outbreak.


Pediatricians need to ensure that their patients are fully vaccinated against polio. They also should report any case of flaccid paralysis to their local health departments.


The outbreak in Tajikistan represents 75% of the world’s polio cases so far for 2010. Most polio cases had been associated with India and Nigeria, which have not been certified polio-free.  There also was an outbreak in the Dominican Republic and Haiti in 2000.


[Editors Note]


Jay Colingham MPH


I want to state that this article is myopic in its public health perspective of Polio and only addresses immunization as a standard and failures in countries to meet standards set by the WHO.  Many factors in immunization with disease like Polio range far beyond the simple 90% target that was assumed to be ‘enough’ for elimination in a country. 


The first matter to address about Polio is the matter of environmental spread of disease.  Herd immunity is the condition described where enough people are immunized that those who are not immunized may not come in close contact to another person who was not immunized with enough frequency to spread disease.  In some diseases, that is a high number (Measles has 100% immunization to reach herd immunity in a community).  In Polio, the number is lower and should be set at around 80-85% immunization of the community.  WHO chooses 90% as an immunization buffer because environmental factors may cause immunity needs up to this number.  Polio is spread through fecal-oral contamination making sanitation one of the greatest barriers to disease distribution.  The virus is highly contagious and is known to be spread through toilet water or unwashed hands.  Dr. Brady fails to mention that Tajikistan had a major collapse in infrastructure that brought drinking water, irrigation water, and waste due to flooding.  An event of fecal-water system contamination is the catalyst for many problems and may have enabled Polio to breach herd immunity.  Other suggestions include over-reporting immunization, failed cold chain on oral polio vaccine, and unknown populations.  In any case, environment and changing conditions, such as exposure to unsanitary water, is the reason that the WHO set the standard at 90% immunization instead of 80-85%.


Dr. Brady also wrote that 560 cases of flaccid paralysis are reported in Tajikistan.  This number does not reflect Polio and should be completely omitted.  Many disease cause flaccid paralysis and any doctor knows that acute asymmetrical flaccid paralysis is the actual symptom of 1-2% of patients with paralytic polio.  Additionally, Polio is only considered confirmed after laboratory testing due to the nature of the symptoms.  After you figure that there are 50-100 times more carriers in abortive and non-paralytic polio cases, the number of lab confirmed cases seems trivial.  As of July 13th, 2010, there have been 413 lab confirmed cases.  The whole world has not seen more than 545 lab confirmed cases since the start of the year.  This bogus number and the lack of grammar, spelling, and fact checking, leads me to believe the article was written offhandedly and does not deserve to be published in a journal.


Perhaps the most blaring omission from Dr. Brady’s article is the differences between OPV and IPV.  Oral Polio Vaccine is used in almost every country in the world except the United States.  It is a live-attenuated vaccine with a form of the Poliovirus that does not cause disease.  It is similar enough to the wild-type virus that your body learns to fight it before you are exposed to wild Polio.  Since the vaccine is not inactivated, there is risk of VAPP (vaccine acquired paralytic polio), which gives roughly 1 in 100,000 people the asymmetrical paralytic polio experienced by 1-2% of the wild-type infected population.  IPV, or Inactivated Polio Vaccine, is a form of the virus that is not functional and provides exposure to parts of the virus so that a recipient’s immune system can develop immunity.  IPV requires multiple doses to reach immunity but most people continue to receive booster shots before visiting Polio endemic regions.  IPV can be mixed with OPV and is much more expensive, often costing thousands or times more.  In the United States, IPV is the vaccine of choice because it does not have risk of VAPP.  Even with lower rates of immunization in America, there are better immunization records than in countries where Polio is geographically closer.  In Tajikistan, immunization records are less formal and often do not exist.


Combining better kept records and IPV in the US with a level of sanitation in domestic life that may be considered compulsive, the level for herd immunity may be dramatically less than Dr. Brady thinks.  90% is a target but it would not be surprising to me if 75-80% immunization in the United States maintained community herd immunity.  In Tajikistan, sanitation is using water to rinse.  Soap is not common anywhere and water is considered unfit to drink by the WHO.  As conditions in sanitation and infrastructure continue to deteriorate in Central Asia, diseases like Polio will increase in occurrence and immunization efforts will need to become a major activity like it is in Sub-Saharan Africa.  Un-developing countries like Tajikistan need to be a focus of our efforts to stop endemic spread of disease.  Fear of spread back to the US through the 90% of people with Polio who are asymptomatic is probably not as much of a worry when considering that conditions and immunization in the United States have much greater accuracy to their reported numbers and could be considered better due to greater enforcement of follow up visits for subsequent phases of immunization.