Last Updated

13 Jul 2003

Source: Reuters, May 29, 2002.

Adult Smallpox Immunity Doubtful From Early Jab

LONDON (Reuters) - Adults given smallpox vaccinations as children before the disease was eradicated in the mid 1970s have probably lost their immunity to the highly infectious disease, according to U.S. scientists.

New research in the United States is the latest evidence that people vaccinated decades ago may no longer be protected.

"This study is, to the best of my knowledge, the only one since eradication which tries to look at the durability of immunity," Michael Sauri, director of the Occupational Medicine Clinic in Maryland, told New Scientist magazine on Wednesday.

"It's showing us that after 20 years, immunity is not going to be there."

The study of 621 microbiologists, who were vaccinated again between 1994 and 2001 because of the type of work they do, found that only about 40, or six percent, were still immune to the disease from their earlier vaccinations.

The new research heightens the debate about whether pre-emptive mass vaccinations are needed or if "ring vaccination" of people in an affected area could contain an outbreak of the disease following a bio-terrorist attack.

The Centers for Disease Control (CDC) in Atlanta favors limited vaccination because little is known about what determines long-term immunity.

But Bill Bicknell of Boston University, a former public health official, believes selective mass vaccination may be the best policy because of the threat of the terrorist use of smallpox.

He said vaccination could minimize the impact of smallpox as a weapon and the risk to the general population.

"I am advocating vaccination of first responders -- emergency workers, hospital workers, doctors, nurses and other staff and wider groups of people essential for the maintenance of civil society," Bicknell told Reuters.

He suggested vaccinating about 100,000 emergency and hospital workers and then looking at the side effects and re-evaluating the situation before expanding the program to more emergency workers and later to the public.

Smallpox is one of the world's most feared diseases. It kills about 30 percent of its victims and leaves many others disfigured.