The Ghost of Smallpox Past


healthcare workers will be offered the Health Care and the VA San Diego Healthcare System, have looked at several plausible scenarios for smallpox emergencies. They aren’t writing science fiction. It’s a dead-serious effort to come up with cost-benefit numbers to guide public health readiness and response.

“How likely is a smallpox bioterror attack? That is a matter for the government to judge,” Bozzette tells WebMD. “The president says the risk of imminent attack is low. And from scenarios we’ve analyzed, the range of complexity required to actually carry out these attacks varies quite widely.”

In the worst-case scenario, mass public vaccination would save about 30,000 lives. But there’s a catch. We prevent those “what-if” deaths at a cost of about 500 very real deaths from vaccine complications.

“Our study shows that in order for there to be a substantial advantage for mass vaccination of the public, we would need to be facing a significant threat of a very widespread attack,” Bozzette says.

The surprising conclusion: Mass smallpox vaccination, either before or after a large-scale attack, won’t do much net good. The reason lies in the nature of smallpox itself.

Devastating Disease

Nobody doubts that smallpox is a terrible disease. It kills some 30% of people who get it, and leaves many more terribly scarred for life. There’s no drug that can cure the disease.

It’s quite contagious but generally, direct and fairly prolonged face-to-face contact is required to spread smallpox from one person to another. Smallpox also can be spread through direct contact with infected bodily fluids or contaminated objects such as bedding or clothing. Rarely, smallpox has been spread by virus carried in the air in enclosed settings such as buildings, buses, and trains, according to the CDC.

It takes about 12-14 days for infection to incubate — and by the time a person is ready to spread the disease, that person is very ill. Most cases are spread at bedside. That’s why smallpox should be treated at home or in special facilities, not in hospitals.

Here’s the most important fact. For about four days after exposure to smallpox, a person can still prevent disease by getting vaccinated. So if there is an exposure, public health officials have at least a week to find people who are exposed and to vaccinate them. They have at least several more days to find their close contacts and vaccinate them, too.

“Conventional methods of containment — vaccination of contacts and isolation of the ill — work reasonably well,” Bozzette says. “Smallpox is a devastating disease. But it is not an instant killer. It spreads slowly. An epidemic would build over months, and there wouldn’t’ be any cases at all right after first exposure. It is scary, but it doesn’t move like wildfire.”

Dangerous But Not Easy to Get

If this doesn’t sound like the smallpox you’ve come to fear, listen to Thomas Mack, MD, MPH, professor of preventive medicine at the University of Southern California, Los Angeles. Mack led teams that traced some 100 smallpox outbreaks as part of the world war to eradicate the disease. He uses the same words as Bozzette: Smallpox doesn’t spread like wildfire.

“People greatly exaggerate the danger to the population not directly affected,” Mack tells WebMD. “It is more like a grenade than like a dirty bomb. Once the initial wave of infections is over, mopping up is relatively simple. It is hard work, but having a couple of weeks between infection and symptoms makes it possible to respond. I won’t say we can protect the people hit in an initial attack. But even if the virus did get a lot of people, we could still contain it. And it would be over in a matter of months.”

Here’s the bottom line. If you’re worried about smallpox, talk to your doctor about it. Find out about your risk from the vaccine. If you feel it’s worth it for your family’s peace of mind and safety, learn how to get the vaccine. In some areas you can sign up for skin rash. Then — if a supply of VIG is available — you decide OK, I’ll get the vaccination. I’ll have a sore arm, maybe a swollen arm, but I am quite willing to accept a one-in-a-million or less chance of death. … It is the risk people face every day they get in the car and go to work.”