U.S. government stockpiles new, safer smallpox vaccine

Updated 37m ago
By Steve Sternberg, USA TODAY

The U.S. government has begun bolstering its smallpox vaccine stockpile with a new version designed to close a gap that left millions vulnerable to a bioterror attack.

The vaccine, Denmark-based Bavarian Nordic's Imvamune, is made with modified vaccinia ankara, a safer alternative to the cowpox vaccines used for generations. Company officials say the first shipments arrived in the U.S. Strategic National Stockpile last week, within hours of a World Health Organization ceremony marking eradication of the disease, widely regarded as one of the great public health achievements of all time.

For thousands of years, smallpox was one of the world's most prolific killers. In the last century of its existence, smallpox is estimated to have killed at least half a billion people. All the wars on the planet during that time killed perhaps 150 million. In the contest of Smallpox vs. War, war lost, Hot Zone author Richard Preston wrote in his forward for the book Smallpox —The Death of a Disease: The Inside Story of Eradicating a Worldwide Killer by D.A. Henderson, leader of the eradication effort.

The virus still lives

The threat has not entirely faded, however. Though natural transmission has ceased, the virus lives in freezers at the Centers for Disease Control and Prevention in Atlanta and possibly in Russia, where Soviet scientists are believed to have created tons of weaponized smallpox. The breakup of the Soviet Union and the rise of global terrorism led the USA a decade ago to begin stockpiling vaccine.

"In June 2001, we had 12 million doses of smallpox vaccine for a population of 280 million," says Randall Larsen, CEO of the non-profit Weapons of Mass Destruction Center. Today, he says, the national stockpile contains 300 million doses of standard smallpox vaccine. "In effect, we have eliminated smallpox from the category of weapons of mass destruction," at least in the U.S., Larsen says.

Vaccination can protect against smallpox even after infection.

But standard smallpox vaccine can cause severe complications. Made with weakened cowpox — a cousin of smallpox— the vaccine's live viruses reproduce in humans, who can infect those around them. People with weakened immune systems and those with a skin condition called eczema are vulnerable to potentially deadly vaccine-related infections. People with those complications, and those in close contact with them, make up as much as 25% of the U.S. population, experts say.

2003 effort was shunned

A 2002-03 government campaign to vaccinate health care workers against smallpox ended when many workers, concerned about the side effects, shunned the vaccine.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which helped to fund development of the new vaccine, says its safety was the "most compelling" reason that he decided to back it. ?The major stumbling block, when we tried to vaccinate people several years ago, was safety,? he says.

The new MVA vaccine is essentially a virus that has lost the genes that allow it to replicate in humans, but keeps the genes needed to induce an immune response. Over the past five years, Bavarian Nordic has carried out trials in hundreds of patients, many of them with eczema and HIV, and many more who are elderly. "In none of these have we seen the side effects that we've seen with the old vaccine," says CEO Anders Hedegaard.

Hedegaard says. And because it?s injected, not scratched into the skin, it doesn?t cause the scarring that occurs with classic smallpox vaccine.

Bavarian Nordic's initial contract calls for the company to supply the U.S. with 20 million doses, enough to protect 10 million people, with an option to buy 40 million doses more.

The Food and Drug Administration approved the vaccine for stockpiling based on its safety profile and tests showing that the vaccine generates an immune response like that of the old vaccine. Bavarian Nordic now plans to carry out a new round of safety and consistency trial in 3,000 more patients. Testing its effectiveness will be a bigger challenge, because no one would consider exposing human volunteers to smallpox. Monkeys will stand in for humans, monkeypox for smallpox, Hedegaard says. ?If we succeed, it?ll be the first vaccine approved through the animal route.?

Smallpox may not be the only bug MVA is poised to battle. The company is now testing MVA-based anthrax, HIV and measles vaccines, made by packing components of those bugs into MVA. The company is now testing five prototype anthrax vaccines in rabbits to see whether any of them generates a big enough immune response to protect them against anthrax. Anthrax is much easier to test because the spores are found widely in soil. Prostate and breast cancer vaccines are also in the works, says Paul Chaplin, the company?s chief scientist.

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