Via Newsweek, Maryn McKenna writes a must-read article: Critical Vaccine Shortage Threatens Polio Eradication Efforts. Excerpt:
The international campaign to eradicate polio, which has vaccinated 2.5 billion people since it began in 1988—nearly all of them children—has faced one setback after another. Its goal of wiping out the disease from the planet, which was meant to happen in 2000, is about 16 years overdue—but getting close. The campaign has confined the disease to only three countries and hopes to reach its goal by the end of this decade.
Now, however, the fight faces a new threat: a critical shortage of vaccine.
The campaign—conducted by the World Health Organization (WHO), the U.S. Centers for Disease Control and Prevention (CDC), UNICEF, Rotary International and the Bill and Melinda Gates Foundation—was expecting to receive 110 million doses of injectable polio vaccine (IPV) this year, but the two manufacturers have told the groups they can supply only about half that.
“We don’t have specifics, but something is preventing the scale-up of vaccination production,” says Shanelle Hall, director of UNICEF’s supply division. “We are projecting now that we won’t have the quantities we need until 2018.”
More than 100 countries are depending on those doses. Without them, planners worry that the eradication campaign will lose momentum, and so many children will go unprotected that there will be fresh outbreaks.
Two Vaccines, Multiple Strategies
Polio vaccination strategies are complicated but come down to this: Since the 1950s, there have been two vaccines, Jonas Salk’s injectable formula, which uses a killed virus to evoke an immune response, and Albert Sabin’s oral version, which relies on a weakened live virus to do the same thing.
Salk’s vaccine was adopted by the industrialized world, but when eradication efforts began elsewhere, the people behind that campaign decided to rely on the oral poliovirus vaccine, known as OPV. That was partly because the drops are less expensive to buy and administer, because they can be given by volunteers with no medical training.
But it was also because the weakened vaccine virus performs a trick that the Salk virus cannot: It reproduces in the guts of children and then is expelled in their feces—and when it enters the environment, it can create immunity in anyone who accidentally ingests it, creating a kind of passive immunization.
That ability to reproduce and spread is a marvelous tool, one that has an unintended consequence. The attenuated virus can mutate back to a disease-causing type, and when it reproduces, it spreads infection instead of protection. Last year, there were only 74 cases of polio in the world, and 32 were caused by a “vaccine-derived” virus.
To reduce the chances of that happening, the campaign switched all of the countries using OPV from one formula to another in April. The abandoned formula contained weakened versions of all three strains of poliovirus (dubbed type 1, 2 and 3). The new formula contained only types 1 and 3. The campaign removed type 2 because that strain has been eradicated in the wild—it has not been picked up by any surveillance mechanisms since 1999—and because it was more likely to mutate into the disease-causing type, compared with the other two strains.
Planners acknowledged the strategy held some risk; it raised the possibility of a type 2 outbreak, if that strain of virus reappeared or if a vaccine virus still in someone’s system mutated and escaped. That risk was supposed to be nullified by a second strategy: In every country still using OPV, children were also supposed to receive one shot of the injectable vaccine, because it contains all three strains and, being a killed-virus vaccine, does not lead to reproduction.
That clever plan was working, but now IPV is running short. “Every child born since May, if they live in a country that does not have access to IPV, is not getting any immunity against the type 2 poliovirus,” says Dr. Stephen Cochi, a pediatrician who leads the CDC’s polio eradication effort. “If we get an increased supply of IPV, we can catch up to those children. Before then, we have to depend on no vaccine-derived poliovirus outbreaks occurring.”