Vaccinated British man found shedding live polio virus for 30 years

LONDON: A British man with an immune deficiency has been found to be shedding a highly virulent, mutant strain of polio virus for nearly 30 years.
The news has come as a major warning for India which was declared polio free on March 24, 2014.
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UK’s National Institute for Biological Standards and Control analyzed more than 100 stool samples collected between 1995 and 2015 from a British white male who had received a full course of childhood immunizations, including the highly effective oral polio vaccine at 5, 7, and 12 months, with a booster at about seven years of age.
Scientists have now confirmed that the subject has been suffering from an immunodeficiency, which affects the ability of the immune system to kill viruses in the digestive tract.
To their horror, the researchers found high levels of type 2 polio virus in all the stool samples analyzed – each sample able to cause paralysis in transgenic mice that had a human poliovirus receptor.
This strain of poliovirus 2 was eradicated from the wild way back in 1999.
Further analysis of the RNA of these iVDPV strains (strains of vaccine-derived polio virus from immune-deficient individuals) by Javier Martin and colleagues showed that the excreted viruses were different from the weakened vaccine strain, and that they had started to diverge from it an estimated 28 years ago, around the subject’s last known vaccination with OPV.
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All iVDPV strains had mutations that reversed the features of the vaccine strain and over time they also acquired a range of other mutations, many affecting the antigenic structure of the virus.
At present, all but two countries worldwide, Pakistan and Afghanistan have been declared polio free.
Louis Georges Arsenault, Unicef representative to India told TOI at the side-lines of the Call to Action Summit: “Let’s understand one thing for sure – till there is one child infected with polio in this world, every other child is at risk of getting infected. The virus is still at large in India’s neighbouring countries. Pakistan is doing better than Afghanistan however in controlling the spread of the virus this year.”
Anuradha Gupta, deputy CEO of GAVI Alliance for Vaccines, who spearheaded India’s fight to eradicate polio told TOI, “This is a shocking finding and highlights that the world needs to have zero tolerance for a single missed child who hasn’t received the full range of vaccinations. The world is closest to wiping out the disease than ever before and we can’t have the virus lurking anywhere if we are looking to eradicate it. We therefore need to see vaccination rates go up across the world. Presently we are missing 15 million children globally for a basic vaccine like DTP 3.”
The good news however is that despite the extensive changes found in the iVDPV strains compared with the vaccine strain, the researchers found that human sera readily neutralized even the most divergent strain.
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“This indicates that vaccinated humans are well protected against infection with these highly drifted iVDPV strains,” the said.
However, they also state that “because the sera tested correspond to a selected group of UK healthy adults between 28-65 years of age who had been vaccinated with a full course of four OPV doses plus at least one dose of Injected Polio Vaccine (IPV), whereas the UK switched from OPV to IPV for polio immunization in 2004, it would be helpful to test sera from cohorts that have only received IPV.”
The finding has worried experts globally who say that patients like this one could start new polio outbreaks.
There are three strains of wild polio virus (1, 2, and 3) and two different types of polio vaccine.
The authors of the study say that IPV is safe and effective in inducing neutralizing antibodies that protect against paralytic polio. It does not, however, induce substantial mucosal immunity and so prevent excretion of virus. OPV which contains weakened or attenuated live virus is effective, and besides neutralizing antibodies induces mucosal immunity, thereby killing viruses in the gastro-intestinal tract and reducing excretion.
Putting the research into context of other studies on iVDPV, the researchers emphasize that “of the total of 73 iVDPV cases that have been described between 1962 and 2014, only seven involved infections lasting more than five years. The case described here represents by far the longest period of excretion described from such a patient and the only identified individual known to be excreting highly evolved vaccine-derived poliovirus at present”.
However, the researchers also mention that several highly mutated VDPV strains that showed molecular properties typical of iVDPVs have recently been isolated from sewage samples in Slovakia, Finland, Estonia, and Israel, suggesting that an unknown number of chronic excreters exist elsewhere.
The researchers conclude that “enhanced surveillance including sewage sampling and stool surveys to search for the presence of iVDPV strains and the development of efficient anti-viral treatments to interrupt virus replication in immune-deficient individuals are needed to be able to identify and manage the possible risks of iVDPV strains spreading and causing disease in patients and the general population, particularly in the light of changes in vaccination strategies as part of the polio eradication endgame and the absence of an established outbreak response strategy.