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How effective is Polio vaccine?
According to the CDC, 99 percent of people develop blood antibodies considered to be protective against polio after 3 doses of inactivated poliovirus vaccine (IPV); however, the duration of vaccine-acquired immunity is not known.
IPV is limited in its ability to induce mucosal immunity and is less effective at preventing the poliovirus from replicating and shedding in the intestines. As a result, persons who receive IPV, the only poliovirus vaccine available for use in the US, may be personally protected from developing paralytic polio but remain capable of transmitting the poliovirus to others through fecal-oral transmission.
The oral poliovirus vaccine (OPV), while not in use in the United States, continues to be administered in most developing countries as part of the Global Polio Eradication Initiative (GPEI). This live vaccine is used in developing countries for several reasons, including cost effectiveness (less than 20 cents per dose) and ease of administration (oral vs. injection).
Persons vaccinated with OPV, however, can still be infected, shed, and transmit wildtype poliovirus.
In 2010, researchers studying asymptomatic wild-type poliovirus transmission in India among healthy vaccinated children admitted that “mucosal immunity induced by OPV is imperfect” and concluded that:
“Although OPV is protective against infection with poliovirus, the majority of healthy contacts who excreted wild-type poliovirus were well vaccinated. This is consistent with a potential role for OPV-vaccinated children in continued wildtype poliovirus transmission and requires further study.”
In July 2014, a study by European and U.S. researchers investigating wild-type polio outbreaks in 2010 among older children and adults in the Republic of Congo and Tajikistan, concluded that “intestinal immunity to poliovirus wanes over time, allowing individuals vaccinated with oral polio vaccine (OPV) to become re-infected and shed poliovirus.” Additionally, study authors stated that the “Global Polio Eradication Initiative is considering expanding the age range of vaccination campaigns even in the absence of adult cases, because of concerns about imperfect, waning intestinal immunity.”
OPV can cause vaccine-strain paralytic polio (VAPP) but according to the GPEI, the estimated rate of 2 to 4 cases of paralytic polio per 1 million births is considered an acceptable risk for most public health officials.
In addition to VAPP, OPV can also cause vaccine-derived poliovirus (VDPV). OPV is a live virus vaccine and individuals who receive the vaccine will shed vaccine-strain poliovirus in the stool for several weeks after vaccination. In areas with poor sanitation, the vaccine-strain virus can spread within a community for an extended period. When this occurs, the vaccine-strain polio virus will undergo genetic changes and, in some cases, transform into circulating VDPV (cVDPV) and cause paralysis. Public health officials report that cVDPV occurs in communities that lack immunity, or due to poorly administered vaccination programs.
In 2008, U.S. and European health officials analyzed eight outbreaks of paralytic polio between 2000 and 2005 in Hispaniola, Indonesia, Egypt, Philippines, Madagascar (2), China and Cambodia that were caused by circulating vaccine-derived poliovirus (cVDPV). Health officials admitted that “it is now known that vaccine viruses can be serially transmitted through human hosts, and may revert genetically toward wild-type transmissibility and virulence.” They also reported that:
“Although only 114 virologically confirmed paralytic cases were identified in the eight cVDPV outbreaks, it is likely that a minimum of hundreds of thousands, and more likely several million individuals were infected during these events, and that many thousands more have been infected by VDPV lineages within outbreaks which have escaped detection.”
They concluded by stating that “Our estimates of the extent of cVDPV circulation suggest widespread transmission in some countries, as might be expected from endemic wild poliovirus transmission in these same settings.”
In September 2015, following the announcement that type 2 wild-type polio had been eradicated globally, public health officials moved quickly to stop use of the trivalent OPV (vaccine containing vaccine-strain poliovirus types 1, 2, and 3) and replace it with a bivalent OPV containing only vaccine-strain poliovirus types 1 and 3. This initiative was implemented to stop the spread of type 2 cVDPV (cVDPV2) that had caused multiple cases and outbreaks of polio in several countries.
Despite removing type 2 polio from OPV in the spring of 2016, cVDPV2 associated paralytic polio cases have continued to occur. In 2019, cVDPV2 outbreaks were reported in the Philippines, and multiple African countries. As a result, since April 2016, approximately 300 million doses of a type 2 OPV have been administered in regions experiencing outbreaks of cVDPV2. Problems arising from the reintroduction of the live type 2 OPV have included the risk that its use will potentially lead to additional cases and outbreaks of cVDPV2.
Public health officials acknowledge that polio will not be eradicated until OPV is no longer in use; however, experts are not certain whether the exclusive use of IPV will be able to maintain eradication status. Concerns include the vaccine’s inability to fully halt poliovirus transmission, and the fact that some individuals can shed the poliovirus for years.
Certain people vaccinated with OPV can excrete poliovirus in their feces for months to years after vaccination. While this occurs primarily in children who are immunocompromised, it has also been reported to have occurred in healthy individuals.
Persons who excrete the vaccine-acquired poliovirus vaccine long-term usually have B-cell-related primary immunodeficiency diseases and what is referred to as infectious VDPV (iVDPV). In these individuals, the vaccine-acquired poliovirus frequently reverts into a virulent strain which often causes paralysis. Individuals who shed the poliovirus for extended periods of time can reintroduce and spread poliovirus within a community. According to the published literature, as of 2018, 107 individuals have been identified as having iVDPV.
While the GPEI plans to stop use of the OPV after wild-type poliovirus has been declared eradicated, the risk of VDPV will continue because of individuals with iVDPV. Polio experts report that surveillance of poliovirus shedding in persons with primary immunodeficiency will be crucial because of their potential to restart polio outbreaks within the population.
In 2019, following numerous outbreaks of cVDPV, some infectious disease experts strongly argued for a halt to the three decade WHO-led Global Polio Eradication Initiative (GPEI) and a transition to a more achievable program of systematic, sustained control of polio. In their argument, published in the BMJ Global Health Journal they state:
“…even successful eradication of poliovirus may not mean an end of polio-like illness. Other viruses from the same family (eg, enteroviruses D68, D71) may produce flaccid paralysis resembling poliomyelitis, with outbreaks reported from a number of industrialised countries in recent years. The existence of other causes of disease does not mean that eradication of one cause should not be attempted. However, it would bring about the challenge of explaining to the world community why outbreaks presenting with the clinical symptoms of a disease eradicated at substantial cost continue to occur.”
The authors concluded that:
“In 2019, the world ‘is at a critical point in polio eradication.’ This could be the year to implement the lessons learnt from GPEI and to move from the eradication goal to sustained polio control, as had already been proposed by leading experts on smallpox eradication more than 10 years ago….. In conclusion, there are two strategies that the world should not be content with: first, unsystematic and uncoordinated polio control efforts, implemented by individual countries acting on their own. Second, continued polio eradication efforts offering simply more of the same. Urging ‘all involved in the effort to excel in their roles’ to achieve polio eradication is just such a strategy. It merely pours more money into an ultimately unsustainable vertical programme.”
In a WHO statement published in October 2019, health officials reported an increase in wild-type 1 poliovirus cases (WPV1) in Pakistan and Afghanistan, and a significant increase in cases of cVDPV2 this year in multiple countries giving children the OPV and stated the following:
“The Committee is gravely concerned by the significant further increase in WPV1 cases globally to 73 in 2019 year to date, compared to 15 for the same period in 2018, with most of the increase due to the ongoing outbreaks in Pakistan… The multiple cVDPV2 outbreaks on the continent of Africa are now at unprecedented levels and need to be treated by countries as a national public health emergency…Furthermore, the global nature of the risk is highlighted by the appearance of cVDPV2 in China and the Philippines, with undetected transmission for about a year in China, and much longer in the Philippines.”
Although there were five times as many cases of wild-type polio in 2019 than in 2018, most of the paralytic polio cases identified and reported in 2019 were caused by outbreaks of cVDPV2 that occurred in Niger, Nigeria, Cameroon, Benin, Ghana, Ethiopia, Somalia, China, Myanmar, Kenya, Central African Republic (CAR), Angola, Somalia, and Papua New Guinea, Indonesia.
These countries have been among those that have been targeted since 1988 by the GPEI, which have repeated mass vaccination campaigns among child populations using the trivalent OPV, sometimes giving children six to eight doses of the vaccine every year. After the WHO declared type 2 polio eradicated in 2015, polio vaccination campaigns in Africa and Asia have been administering a bivalent OPV that only contains type 1 and type 3 attenuated polioviruses.
WHO officials have reported that the risk of international transmission of wild poliovirus type 1 is increasing and that there is “a rising risk of cVDPV spread” of vaccine-strain poliovirus 2 as cVDPV has spread from Nigeria to Ghana, Benin, and Niger, and from Somalia to Ethiopia.
Despite the increasing risk of both wild-type and cVDPV, the GPEI has set a goal of global polio eradication for the year 2023.
IMPORTANT NOTE: NVIC encourages you to become fully informed about Polio and the Polio vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.