Oct 02 2007

Another Polio Outbreak in Nigeria

Northern Nigeria has seen more than its fair share of polio in recent years, a disaster completely of its own doing. It has made itself into a poignant object lesson in the risks of anti-science and conspiracy theories. Even worse, the world is paying for Nigeria’s irrationality.

Trouble started in 2003 when rumors began to spread in northern Nigeria that the polio vaccine was deliberately tainted to cause AIDS, cancer, and infertility. The local government conspired with religious leaders to spread these rumors and shut down the vaccine program.

Up until that time the Global Polio Eradication Initiative was very successful in distributing vaccines to poor parts of the world and achieving a high compliance. So successful was the program that experts began to predict that total eradication of polio was just around the corner.

Then, the northern Nigerian rumors began to spread, the polio vaccine program was shut down, and predictably cases of polio in northern Nigeria began to increase. A report in Science sums up the situation;

By the end of 2004, the number of polio cases in Nigeria had doubled to about 800, and in 2006 it soared to more than 1100. Wild virus from Nigeria reinfected some 20 other countries, leading to a spike in global cases. It was a huge setback to the Global Polio Eradication Initiative, which estimates that the world spent an additional $500 million to contain the damage. Only recently have global cases dropped back to near preboycott levels.

Now the same Science paper reports that we are entering a second phase of the setback, and outbreak of vaccine-derived poliovirus (VDPV).

Polio, short for poliomyelitis (myelitis means inflammation of the spinal cord) is caused the polio enterovirus. There are three strains of this virus, types 1, 2, and 3. Type 2 polio virus has been eradicated from the wild and exists only in vaccines. Types 1 and 3 still exist as wild type virus. The polio virus enters the body through the mouth and infects the anterior horn cells of the spinal cord – these are the neuronal cells that give rise to the nerves that connect to muscles. As these motor neurons die the muscles become weak and eventually atrophy.

One vaccine for polio is an oral trivalent vaccine – because it contains all three types of virus. The viruses in the vaccine are attenuated, meaning that they are alive but are weak. This allows the body to fight off the weak form of the virus and build up immunity that will protect against the wild forms of the virus. Rarely, however, the weakened form of virus in the vaccine by spontaneously mutate back to the more virulent wild type, and therefore it is possible to get polio from the live oral vaccine.

There is also an inactivated polio vaccine that uses a dead virus. This is just as effective without the risk of infection, but is more expensive. Attempts are under way to phase out the oral vaccine and replace it with the inactivated vaccine, but there is still heavy reliance on the oral vaccine.

It now appears that an outbreak of VDPV has occurred in northern Nigeria. There are several cases of polio where the type 2 strain has been isolated – and since this strain exists only in the vaccine it must have come from a vaccine. Even worse, it appears that the vaccine derived virus has spread from person to person, leading to a fresh outbreak of polio in northern Nigeria.

Normally the rare case of VDPV does not cause an outbreak because of herd immunity – enough of the population is vaccinated to prevent spread. However, northern Nigeria’s low vaccination rate has created an environment in which the VDPV can spread. Further, spreading of the VDPV among unvaccinated people creates the opportunity for mutation back to the wild-type virus.

Now authorities are really in a pickle. The people of northern Nigeria are already suspicious of the vaccine. If they feel the vaccines are now unsafe (which they are not – there is no more risk of getting polio from the oral vaccine than normal, the only difference is that the risk of spread is greater because of the low vaccination rates) this could kill the fragile compliance that now exists. Any delay, however, it likely to be viewed as secrecy and can be used to support fears of a conspiracy.

In the final analysis hopefully this will be just another speedbump on the road to polio eradication. But it is a costly one, in dollars and in lives. The whole affair could have been avoided with adequate vaccine compliance, or rather it was caused by the use of vaccines as a propaganda tool to provoke fear and hysteria.

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2 responses so far

2 Responses to “Another Polio Outbreak in Nigeria”

  1. ziggyon 05 Oct 2007 at 12:24 am

    There’s a similar situation reported by the BBC in Zimbabwe. Some archbishop is claiming that some European condoms being distributed by AIDS relief workers are deliberately tainted with HIV. http://news.bbc.co.uk/2/hi/africa/7014335.stm?TB_iframe=true&height=500&width=750

    When the Catholic Church opposes the use of condoms, THEY’RE SERIOUS!

  2. funda62on 05 Oct 2007 at 3:37 am

    Do you think it is possible that this outbreak could spread to other countries due to decreased immunization compliance? How long after infection does it take for an individual to show symptoms?

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