WASHINGTON -- Findings by U.S. scientists could help authorities here and abroad determine who should receive treatment first in the event of a smallpox outbreak in which the number of patients outstrips the available supply of vaccine (see GSN, April 24).
(Dec. 11) -
A U.S. Army medical technician administers the smallpox vaccine in 2002 (Stephen Morton/Getty Images).
Tests of blood serum from U.S. citizens vaccinated up to 88 years ago determined that nearly all maintained levels of protective antibodies that would appear sufficient to protect them from infection, National Institutes of Health researchers said in an article published this month in the American Journal of Medicine.
“Our research should help public health officials in the U.S. and in other countries as they make decisions relating to vaccine supplies,” one of the authors, National Institute of Aging immunologist Dennis Taub, said in a prepared statement. “Our data imply that limited supplies of vaccine can be more usefully applied to people who have never been vaccinated, primarily those born after 1972.”
One expert, though, questioned the results of the study and whether people in a crisis situation would agree to forgo or delay vaccination in favor of others.
The NIH researchers have “never worked in doing anything like this, I can tell you. No. [Potential victims] would all want to be vaccinated,” said D.A. Henderson, who for more than a decade led the successful international effort to eradicate smallpox.
Smallpox was eliminated from nature in 1977 after killing hundreds of millions throughout history. U.S. citizens under age 35 have generally not been immunized, while older Americans would not have received booster shots after the early 1970s.
However, Russia and the United States keep stocks of smallpox for research purposes, creating the potential for material to be diverted for an act of terrorism. The infectious disease is considered a Class A select agent, which “pose the greatest potential threat for adverse public health impact and have a moderate to high potential for large-scale dissemination,” according to the Centers for Disease Control and Prevention.
Tabletop war games conducted in the United States since 2001 have postulated devastating acts of bioterrorism involving smallpox. One exercise, Dark Winter, included a projection of 3 million infections in less than two months, with one-third of the victims dying.
Experts, meanwhile, continue to argue over the likelihood of a large-scale incident involving a disease agent (see related GSN story, today).
The United States possesses 286 million doses of smallpox vaccine, enough “to vaccinate everyone if smallpox should appear again in this country,” said CDC spokesman Von Roebuck. He expressed confidence in the government’s ability to provide rapid treatment to a large number of victims.
Taub acknowledged that the U.S. smallpox vaccine situation has improved in the years since the study began, in 2003-2004.
Work started “with the idea that in the post-9/11 era with the possibility of bioterrorism attacks we need to know what kind of immunity we carry to various pathogens, and ones to which we’ve been vaccinated, such as smallpox,” Taub said in an interview with Global Security Newswire.
The old Dryvax smallpox vaccine, which is no longer in the U.S. stockpile, also had been found to cause side effects in the elderly and people with suppressed immune systems, Taub said: “You don’t want to give the vaccine if it’s not necessary. That was another point.”
Researchers studied 246 people who have been involved in a 50-year study in the Baltimore area of normal aging. Of those, 209 had received at least one smallpox vaccination between 13 and 88 years ago, while 18 had medical histories documenting childhood smallpox. The rest had not been vaccinated or suffered through smallpox.
Tests of multiple serum samples provided over decades by the vaccinated participants found that 97 percent retained levels of antibodies — including the crucial “neutralizing,” or protective antibodies — comparable to those individuals who had lifetime immunity after surviving smallpox during childhood.
Also, in contrast to previous recommendations suggesting the need for smallpox vaccine boosters every five years, the study found that additional shots might not be necessary as they provided limited increases in antibody counts and virus neutralization.
“Our research shows that if you were ever vaccinated against smallpox or if you ever had the disease itself, it’s quite likely that your immunity has continued and revaccination isn’t necessary,” Taub said.
Henderson praised the researchers but questioned their findings in this case. It remains largely unknown “what level of antibody and what type of antibody would serve to protect somebody against smallpox,” he told GSN.
Studies to determine the lifespan of smallpox immunity have been foiled by a number of variables, including determining when a person was successfully vaccinated, said Henderson, now with the University of Pittsburgh’s Center for Biosecurity. He also said that studies prior to the disease’s eradication found a significant number of smallpox patients -- several thousand in India -- who had been vaccinated.
“The bottom line on this is quite simple, and that is if we had an outbreak of smallpox we would advise again vaccinating everybody who had any reasonable chance of being in contact with a patient, just as a matter of precaution,” Henderson said. “Here you’ve got a disease with a 30 percent death rate, you don’t want to take any chances.”
Taub also offered a word of caution about the findings. Comparable antibody levels in those known to be immune to smallpox and people who received vaccinations do not necessarily ensure they have equal resistance to the disease. Antibody levels might offer a “false positive” for immunity, which could derive from some other factor, he said.