Poliovirus type 2 returns

17 August 2009

polio-immunizationThe global battle to eradicate poliomyelitis is already 9 years behind schedule. To make matters worse, type 2 poliovirus, which was declared eradicated in 1999, has returned.

There are three serotypes of poliovirus, each of which causes poliomyelitis. The vaccine used by WHO in the global eradication effort is a trivalent preparation comprising all three serotypes. When type 2 poliovirus was eliminated, many countries began using monovalent type 1 and type 3 vaccines: one vaccine for type 1 and another for type 3. As a consequence of this immunization strategy, population immunity to type 2 poliovirus declined. But if type 2 poliovirus was eradicated, where has it come from?

It came from the poliovirus vaccine.

The trivalent vaccine that is used in the eradication effort is an infectious vaccine. The vaccine is ingested, the viruses replicate in the intestine, and immunity develops. Viruses of all three serotypes undergo genetic changes during replication in the alimentary tract. As a consequence, the vaccine recipient excretes neurovirulent polioviruses. These so-called vaccine-derived polioviruses (VDPV) can cause outbreaks of poliomyelitis in non-immune people, as described in Polio among the Amish.

The outbreak of type 2 poliovirus in Nigeria began in 2006. There have been 126 cases of paralytic disease reported so far in 2009. Before 2003, the year that Nigeria began a boycott of polio immunization, the trivalent vaccine was used. Immunization resumed with monovalent types 1 and 3 vaccine in 2004. Therefore the source of the VDPV type 2 is most likely the trivalent vaccine used before 2003.

The resurrection of type 2 polio highlights the difficulties involved in using an infectious viral vaccine to eradicate the disease. In reality, type 2 poliovirus was not eradicated in 1999, because that virus was still present in the trivalent vaccine that was being used. Clearly the virus was still circulating in humans, despite the fact that no type 2 poliomyelitis was observed.

In response to the type 2 outbreak in Nigeria, trivalent vaccine is being used again. It’s not difficult to imagine that this will lead to another cycle of eradication and emergence of type 2 polio. What’s the solution to this apparently endless circle? Use inactivated poliovirus vaccine, which I’ve been dreaming about for some time.

Roberts, L. (2007). Vaccine-Related Polio Outbreak in Nigeria Raises Concerns Science, 317 (5846), 1842-1842 DOI: 10.1126/science.317.5846.1842

Roberts, L. (2009). Type 2 Poliovirus Back From The Dead in Nigeria Science, 325 (5941), 660-661 DOI: 10.1126/science.325_660

Jegede, A. (2007). What Led to the Nigerian Boycott of the Polio Vaccination Campaign? PLoS Medicine, 4 (3) DOI: 10.1371/journal.pmed.0040073

  • http://theartfulamoeba.com/ Jennifer Frazer

    Wow. This reminds me of the theme of Edward Tenner's book, “Why Things Bite Back: Technology and the Revenge of Unintended Consequences”. The more we try to fix things, the more we can sometimes end up making them more complicated for ourselves, it seems.

  • Emily

    Thank you, Dr. Racaniello, for having this dream. I hope very much that momentum builds to deliver safe, killed polio vaccine to the regions of the world that still need it. It seems imperative to me.

  • mdubuque

    I distinctly and clearly recall the BBC featuring an extensive interview with a representative of the WHO at the time of the Nigerian boycott sneering and scoffing and mocking the absolutely “preposterous” notion that there could be ANY relationship between this vaccination and infection with polio. In fact the BBC speculated that since this revolt against the vaccination program was part of an al Qaeda strategy of disinformation.

    This line of scorn and derision was repeated throughout the AP and Reuters at the time as well.

  • http://www.virology.ws profvrr

    For many years the WHO line was that vaccine-derived polioviruses
    could not cause polio, nor could they be transmitted among humans. The
    outbreak of vaccine-derived disease in 2000 in Haiti and subsequently
    in several other countries changed that incorrect view.

  • http://www.facebook.com/matt.dubuque Matt Dubuque

    I understand and agree.

    But as an informed layperson I could tell at the time that there was at least a shred of competent anecdotal evidence to the contrary.

    And for such a prominent body to heap scorn on those who disagreed in good faith only contributed to the polarization in Northern Nigeria. This phenomenon is NOT unrelated to the strengthening of radical Islam in that area and now al Qaeda is establishing a foothold and more there.

    The end result of this very important event in recent northern Nigerian history is that the credibility of the radical Islamists in that region was dramatically increased among the local population. That's a horrific outcome and heads should roll because of it. The people of Northern Nigeria are hot as Hades about the entire episode, as they well should be.

    I remember hearing a local leader speaking on the subject at the time. I was expecting to hear some blathering idiot, which is how the BBC treated his commentary. But after listening carefully to his views, I could not exclude the possibility that he could be at least partially correct. I was stunned. It seemed that there was just too much smoke there to exclude further inquiry. Something was clearly going on.

    At the time, I recall polio was on the ropes. This was the last area in the world, to my knowledge, where polio existed. Then I watched over the years with horror and dread as it reappeared in several nations.

  • 33ff

    So, in other words: The vaccine doesn't work, therefore, we must use more vaccine?

  • Emily

    Instead of heads rolling, I think more good would be done by using global resources to take care of the victims of vaccines gone bad. The lives of those children and their families are altered forever either way, but I don't think they would all hate and mistrust the people that brought that vaccine into their country if those people acted responsibly now. If the victims are abandoned, they will feel badly used by the herd, and rightly so.

  • jojo

    Administration of live polio vaccine, is likely the organism can revert back to the wild form. all it is because of viral genetic recombination mutant to access the virulent genes from wild strain from the environment or resovoir host. be careful WHO it will be pandemic.

  • http://www.virology.ws profvrr

    Poliovirus vaccine strains revert to virulence which multiplying in
    the human gut. Reversion is not a consequence of recombination with
    wild type strains as you suggest. This is clear for the type 2 strain
    as the wild type virus had been eradicated. There is no reservoir host
    for poliovirus other than humans.

  • jojo

    Administration of live polio vaccine, is likely the organism can revert back to the wild form. all it is because of viral genetic recombination mutant to access the virulent genes from wild strain from the environment or resovoir host. be careful WHO it will be pandemic.

  • http://www.virology.ws profvrr

    Poliovirus vaccine strains revert to virulence which multiplying in
    the human gut. Reversion is not a consequence of recombination with
    wild type strains as you suggest. This is clear for the type 2 strain
    as the wild type virus had been eradicated. There is no reservoir host
    for poliovirus other than humans.

  • Jojo97

    try this website NOW it helped 50% of the public

  • Pingback: Vaccine-associated poliomyelitis in Pakistan()