Date: Wed 12 Nov 2014
Source: VOA (Voice of America) News [edited]
Researchers identify vaccine-resistant polio strain
As the world enters the final phase of a global polio eradication effort, French researchers have identified a mutant strain of the virus that is resistant to the polio vaccine. Despite this, an American expert said the war on polio can be won with continued vaccination.
Despite progress toward the goal of wiping polio off the face of the Earth with an aggressive child vaccination campaign, transmission of the paralytic illness continues in Nigeria, Pakistan and Afghanistan. Now, a mutant strain of the virus responsible for a deadly outbreak in the Republic of the Congo in 2010 has been discovered, rendering the polio vaccine less effective.
Scientists at the French organization Institute of Research for Development, or IRD, found the mutant strain. They tested it on 60 blood samples from vaccinated volunteers in Congo and neighbouring Gabon. Antibodies raised by the vaccine were found to be ineffective in neutralizing the virus in 15 to 30 per cent of the samples. The findings were published recently in the journal Proceedings of the National Academy of Sciences.
Walter Orenstein, associate director of the Emory Vaccine Center at Emory University in Atlanta, Georgia [USA], is considered a world renowned expert in the field of infectious diseases and vaccination. He said there is concern the virus may become more virulent. "And there is the theoretical potential of evading the immune system. But I think the bottom line right now is what's said in basically the last sentence of the paper, which said ... mass campaigns using oral polio vaccines stopped the outbreak," he said.
But in some countries, there is violent opposition to those campaigns. Since January , attacks by the Taliban on vaccination teams in Pakistan and Afghanistan have resulted in 235 polio cases, a 15-year high. [The attacks on polio vaccination workers has resulted in geographic areas where vaccination activities are not routinely conducted due to the security concerns for the welfare of the vaccinators. - Mod.MPP] The militants charge the healthcare workers are spies for Washington and the oral polio vaccine makes boys sterile.
Pakistani government officials, saying they don't want to see children paralyzed for life, are vowing to make the country polio-free in 6 months. Orenstein said that's the only way to lessen the threat of a vaccine-resistant strain. "So it to me adds to the urgency of let's just get rid of this virus, and then we won't have to worry about this kind of issue," he said. Orenstein said it's likely polio will be eradicated in Africa by the end of this year , while Pakistan remains the major reservoir. He said stepped-up commitments are needed to vanquish the disease once and for all. [byline: Jessica Berman]
[The article referred to in the above media report is: Drexler JF, Grard G, Lukashev AN, Kozlovskaya LI, Bottcher S, Uslu G, et al. Robustness against serum neutralization of a poliovirus type 1 from a lethal epidemic of poliomyelitis in the Republic of Congo in 2010. Proc Natl Acad Sci USA. 2014 Sep 2;111(35):12889-94. doi: 10.1073/pnas.1323502111. (abstract available at <http://www.pnas.org/content/111/35/12889.abstract
"In 2010, a large outbreak of poliomyelitis with unusual 47 percent lethality occurred in Pointe Noire, Republic of Congo. Vaccine-mediated immunity against the outbreak virus was never investigated. A wild poliovirus 1 (WPV1) isolated from a fatal case (termed PV1-RC2010) showed a previously unknown combination of amino acid exchanges in critical antigenic site 2 (AgS2, VP1 capsid protein positions 221SAAL [-->] 221PADL). These exchanges were also detected in an additional 11 WPV1 strains from fatal cases. PV1-RC2010 escaped neutralization by 3 different mAbs relevant for AgS2. Virus neutralization was tested in sera from fatal cases, who died before supplementary immunization (n = 24), Gabonese recipients of recent oral polio vaccination (n = 12), routinely vaccinated German medical students (n = 34), and German outpatients tested for antipoliovirus immunity (n = 17) on Vero, human rhabdomyosarcoma, and human epidermoid carcinoma 2 cells. Fatal poliomyelitis cases gave laboratory evidence of previous trivalent vaccination. Neutralizing antibody titers against PV1-RC2010 were significantly lower than those against the vaccine strain Sabin-1, 2 genetically distinct WPV1s isolated in 1965 and 2010 and 2 genetically distinct vaccine-derived PV strains. Of German vaccinees tested according to World Health Organization protocols, 15-29 per cent were unprotected according to their neutralization titers (less than 1:8 serum dilution), even though all were protected against Sabin-1. Phylogenetic analysis of the WPV1 outbreak strains suggested a recent introduction of virus progenitors from Asia with formation of separate Angolan and Congolese lineages. Only the latter carried both critical AgS2 mutations. Antigenetically variant PVs may become relevant during the final phase of poliomyelitis eradication in populations with predominantly vaccine-derived immunity. Sustained vaccination coverage and clinical and environmental surveillance will be necessary."
The above mentioned outbreak was associated with a much higher case fatality rate than had been seen -- 47 per cent. At the time of the outbreak, there was speculation that perhaps the high lethality observed was related to a reporting artifact, where only the more serious cases were brought for medical attention, thereby erroneously elevating the observed case fatality rate. A Eurosurveillance report about the outbreak, which detailed studies on the outbreak associated viruses also mentioned a "putative" association with an enterovirus 109 in addition to the WPV1 identified (see Poliomyelitis - worldwide (28): Rep of Congo, Asia, Russia 20101126.4272 for the full report). This new PNAS study provides more in-depth analysis of the WPV1 involved, demonstrating there had been mutations in the virus resulting in a more virulent virus with reduced immunologic protection provided by vaccine induced antibodies.
Genetic sequencing of the WPV1 identified it as a virus known to be circulating in Angola at the time (which had originally been imported from India in 2005, then circulated in Angola and the Democratic Republic of the Congo before renewed circulation beginning in 2007 (see Poliomyelitis - Worldwide (07): Angola, Congo DR, Chad, RFI 20070731.2468).
While the documentation of such a WPV is very disconcerting, the fact that transmission of this WPV was interrupted through the accepted vaccination campaigns suggests that the challenges posed by this virus are presently not insurmountable, although the possibility this may change is of concern.
For the HealthMap/ProMED map of the Republic of Congo, see