Last Updated

13 Jul 2003

Source: Washington Post, May 8, 2002.

Studies Cite Smallpox Vaccine Tradeoff

Mass Inoculation Might Kill Hundreds, Save Thousands

By Susan Okie, Washington Post Staff Writer

A mass campaign to vaccinate Americans against smallpox might result in 200 to 300 deaths and make several thousand people severely ill -- yet could save thousands of lives in the event of a bioterrorist attack with the virus, according to research presented yesterday at the Pediatric Academic Societies' annual meeting in Baltimore.

The new estimates came from studies led by pediatricians Alex R. Kemper and Matthew M. Davis of the University of Michigan, who said they hoped their analyses would contribute to an unfolding national debate about whether Americans should be offered a vaccine likely to kill some recipients in the cause of protecting the nation from a possible bioterrorist attack.

"There's no other vaccine that we currently give that carries with it a risk of death," said Kemper. "From a societal standpoint, we have to decide whether or not we're willing to take this risk."

Infectious disease experts will gather in Atlanta today and Thursday to begin drafting recommendations about who, if anyone, should get the vaccine. Public discussions scheduled for Washington and several other cities this summer will focus on whether emergency room personnel and other medical and public health workers should be vaccinated, as well as on the larger question of whether the vaccine should be made available on a voluntary basis to all Americans.

Not everyone is a candidate for smallpox vaccination. People whose immune systems are weakened -- by HIV, cancer, treatment with certain drugs or various other conditions -- cannot safely take the vaccine. Neither can pregnant women, children under 1 year old, or anyone prone to eczema, a skin condition that affects 10 percent of Americans. Those who live with anyone in a high-risk group are also excluded because vaccine recipients can pass vaccinia, the virus in the vaccine, to close contacts. For all of those reasons, Kemper estimated that 25 percent of the U.S. population would be ineligible.

The vaccine's most serious potential side effects are encephalitis (brain inflammation) and progressive vaccinia, in which the sore produced by the vaccine spreads without healing. Either can be fatal. People with eczema who are vaccinated may develop eczema vaccinatum, a life-threatening skin rash.

Based on historical data, Kemper estimated that a campaign to vaccinate U.S. residents between the ages of 1 and 29 would cause 175 cases of encephalitis, 420 cases of progressive vaccinia and 1,200 cases of eczema vaccinatum, with a total of 190 deaths. If the campaign included people between the ages of 1 and 65, there would be an estimated 505 cases of encephalitis, 845 cases of progressive vaccinia and 3,525 cases of eczema vaccinatum, with 285 deaths. In either scenario, thousands of other people would suffer less severe but still significant side effects.

A vaccination campaign would nonetheless be likely to save many lives if smallpox virus were used in a terrorist attack, according to Davis, who also presented his findings yesterday. The government's current plan for containing an outbreak is a strategy called "ring vaccination," in which people with suspected smallpox and their contacts would be traced, vaccinated and isolated from the surrounding population. Vaccinating a person even two or three days after exposure to smallpox offers considerable protection against the disease.

Davis and colleagues used a mathematical model to compare the effectiveness of ring vaccination after an outbreak with the effectiveness of a preventive mass vaccination campaign targeting people between 1 and 29 years old.

If 50 percent of that age group had been previously vaccinated, the number of U.S. deaths predicted from an outbreak that began with 100 infected people would be 358, including vaccine-related deaths. A similar outbreak would be predicted to cause 2,160 deaths if only ring vaccination were used. In a larger outbreak, or one that began in several places at once, the lifesaving effect of preventive vaccination would be even greater.

Davis said that vaccinating children and young adults would help protect older people as well by greatly reducing transmission during an outbreak, because smallpox depends so heavily on person-to-person transmission.

But for a mass vaccination campaign to succeed, Americans would have to accept "some numbers of deaths and several thousand illnesses," Davis noted. "Today's U.S. population is not accustomed to that level of side effects and deaths from a vaccine."

Routine vaccination against smallpox ceased in the United States in 1972, and experts estimate that most or all of the population is vulnerable to infection with the virus, which is highly contagious and carries a 30 percent mortality rate. Although the remaining known stocks of smallpox virus are kept in two high-security laboratories in the United States and Russia, many experts fear that terrorists might gain access to samples of the virus.

In Atlanta, consultants to the federal Centers for Disease Control and Prevention will begin drafting proposals for the Advisory Committee on Immunization Practices (ACIP), which will issue proposed recommendations on smallpox vaccination in June. The first of about a half-dozen public forums is scheduled here on June 25.