Reasonable Rascal
08-30-02, 22:29
SMALLPOX, DURATION OF IMMUNITY
A ProMED-mail post
[1] Date: Wed 28 Aug 2002
Source: United Press International, Wed 28 Aug 2002 [edited] <http://www.upi.com/view.cfm?StoryID=20020828-031526-9415r>
Smallpox Vaccination May Be Effective for Longer Than Assumed Previously
------------------------
Scientists have believed that smallpox vaccine only confers protection against the deadly virus for 10 years, but a new study released on Wed 28 Aug 2002 [published in the current issue of The New England Journal of Medicine] found evidence that people may be covered [protected] for 35 years or more, which could mean many Americans retain some level of immunity.
Routine smallpox vaccinations were halted in the United States in 1972. Given the [accepted] 10-year limit of protection, it was assumed that immunity had long ago worn off and everybody was susceptible to the virus. The new study, which involved lab workers who conduct research with smallpox, found that their immune systems show signs of significant levels of protection up to 35 years [after vaccination]. This finding could change the strategy for vaccinating against smallpox in the event of a bioterrorist attack, Jeffrey A. Frelinger, Chairman of Microbiology and Immunology in the University of North Carolina School of Medicine and lead author on the study, told United Press International.
If an attack occurs before a full stockpile of vaccine is ready, the new findings suggest it would be prudent to first begin vaccinating those born after routine smallpox vaccination was halted. This group of people in the United States would have no protection at all, whereas those born before 1972 likely still retain some immunity. Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases, told UPI: "That is a moot point because we will have enough vaccine." He noted 155 million doses are available now, more than enough to protect the number of potentially exposed people in the event of a bioterrorist attack.
In the study, Frelinger and a colleague drew blood samples from 4 laboratory workers who had been vaccinated against the virus within the past 5 years, and 9 other lab workers who had been vaccinated between 5 and more than 35 years ago. After exposing the blood samples to the smallpox virus, the researchers found the body's immune system cells exhibited a response indicative of the ability to suppress the virus whether the person had been vaccinated 5 years ago or 35 years ago, Frelinger said. Those vaccinated 35 years ago showed some drop-off in activity but it was only a small decline, he noted. They still had 2/3rds the response of people vaccinated 5 years ago. "We don't know if that is enough to protect people because it is unethical to expose these people to smallpox," he said. "But I would guess based on mouse studies that it probably is sufficient."
Rafi Ahmed, Director of the Vaccine Research Center at Emory University in Atlanta, agreed. "We don't know if these people vaccinated long ago retain protective immunity, but we can be pretty sure that these individuals will do better than unvaccinated people," he told UPI. Ahmed noted the findings are supported by a previous study conducted in the early 1990s that found people had active immune responses to smallpox virus for up to 50 years after vaccination. Frelinger also pointed out that during an outbreak of smallpox in Liverpool, England, in 1902, people who had been vaccinated 50 years previously were protected from death and serious disease. The vaccine being used at that time was essentially the same as the one in use today, so this suggests people may be protected for up to 50 years, he said. If it holds true, it would mean people born as far back as 1942 may retain some protection against the smallpox virus, he said. [Byline: Steve Mitchell] -- ProMED-mail
[The assay of antiviral activity employed measured how well the immune system cells known as CD8 T cells responded when the participants were exposed to vaccinia virus (used as a substitute for virulent smallpox virus). Exposure to vaccinia virus produced a strong CD8 T-cell response in people who had been vaccinated in recent years, and the response was still considerable in people who had been vaccinated 5 to 35 years previously. Even those who had been vaccinated more than 35 years previously still had a considerable immune response. In recently vaccinated people, about 6.5 percent of CD8 T cells were activated in response to exposure to vaccinia virus, compared with 4 percent in people vaccinated 35 or more years before. This level of response was considered by the North Carolina workers to represent a substantial level of immunity.
The extent to which cell-mediated immunity induced by vaccinia virus (the vaccine virus) to infection by variola (smallpox) virus cannot be measured. Consequently the observations must be interpreted with caution. Furthermore, the numbers of individuals involved is too small to allow estimation of the range of responses that might be expected in the general population. - Mod.CP]
[2] Date: Thu 29 Aug 2002
Source: The New York Times, Thu 29 Aug 2002 [edited]
Value of Duration of Immunity Experiments Questioned
-----------------------------------------------
Scientists at the University of North Carolina have reported additional evidence suggesting that immunity conferred by smallpox vaccine may last longer than had been thought, at least for some people. But they and other researchers cautioned that the findings, from laboratory blood tests, might not apply to people actually exposed to smallpox.
The study, by Dr. Jeffrey A. Frelinger and Dr. Lawal Garba, involved blood samples from 14 individuals; 13 had been vaccinated one to 35 years earlier and one had never been vaccinated. The researchers, who reported their findings in a letter in the 29 Aug 2002 issue of The New England Journal of Medicine, isolated certain white blood cells from each sample. The cells, known as CD-8 T cells, are part of the immune system. The researchers exposed the cells to vaccinia virus, a relative of the smallpox virus used since the 18th century as a smallpox vaccine. The degree to which the immune system cells responded to the virus offers a rough indication of immunity, the researchers said.
The researchers said the participants could not recall how many times they had been vaccinated. Because they worked with the vaccination virus, 4 of the participants in the North Carolina study had last received smallpox vaccinations within 5 years, according to federal guidelines, and 9 others were vaccinated from 6 to 35 years earlier. The researchers said the samples from all 13 vaccinated participants showed a robust immune response. Dr. Frelinger said that he undertook the study because of the scarcity of data on the durability of smallpox vaccination, and that he was surprised to find how durable it was. He acknowledged, however, that his study involved cells and a laboratory dish and said that it remained to be seen what would happen in the event of a real outbreak.
Because smallpox has occurred in the past among people who have been vaccinated, experts have long known that vaccine-conferred immunity wanes over time, but they do not know exactly how much. Dr. Anthony S. Fauci, the Director of the National Institute of Allergy and Infectious Diseases, said that over the years scientists had come up with contradictory findings. Dr. Fauci said his agency was paying for continuing studies that were using similar tests to measure the durability of immunity among people who had received smallpox vaccine.
But other experts said they were not surprised by the North Carolina findings and doubted their usefulness. Old vaccination can protect against death from smallpox and can modify the course of illness. But health officials say they face a more important consideration in preparing for a bioterrorist attack: even a mild case can transmit the smallpox virus and perpetuate an epidemic. "You can't draw conclusions in the real world from the data" from the North Carolina tests, said Dr. Frank Fenner of the University of Canberra in Australia. Dr. D. A. Henderson, who led the health organization's smallpox eradication effort and who is now a top government adviser on bioterrorism, said he had "no idea" how the new findings correlated with protection against natural exposure to smallpox. Dr. Henderson said it was "perfectly obvious that one successful vaccination does not protect for a lifetime." Health officials once recommended smallpox vaccination every 3 years for travelers to infected areas. "It would be foolhardy to rely on any vaccination more than 3 years old as solid protection," said Dr. J. Donald Millar, a former head of the smallpox eradication program at the Centers for Disease Control and Prevention.
Because scientists did not determine the length of protection from a smallpox vaccination before the disease was eradicated, health officials can only extrapolate from information collected from past epidemics, some as long ago as a century. A study of 1163 cases of smallpox in Liverpool, England, in 1902 and 1903 showed a striking difference between vaccinated and unvaccinated patients in all age groups, both in terms of severity of infection and risk of death. Protection waned as time passed from the last vaccination, but was significant even among those 50 and older, most of whom had been vaccinated in childhood. In 1972, Dr. Thomas Mack confirmed the Liverpool findings in a study of 680 cases of smallpox imported into Europe and Canada from 1950 through 1971. Dr. Mack, a preventive-medicine expert who now works at the University of Southern California, found that the death rate was 52 percent among unvaccinated individuals, 1.4 percent among those vaccinated one to 10 years before exposure, 7 percent among those vaccinated 11 to 20 years before exposure, and 11 percent among those vaccinated more than 20 years before exposure.
[Byline: Lawrence K. Altman]
[Let ́s not get carried away by enthusiasm for this new finding, but let's not discount it either. If there is significant protection against death, that at least is something. And I think D. A. Henderson ́s remark must have been quoted out of context -- one shot of the vaccine against another virus, yellow fever, does protect for a lifetime. - Mod.JW]
A ProMED-mail post
[1] Date: Wed 28 Aug 2002
Source: United Press International, Wed 28 Aug 2002 [edited] <http://www.upi.com/view.cfm?StoryID=20020828-031526-9415r>
Smallpox Vaccination May Be Effective for Longer Than Assumed Previously
------------------------
Scientists have believed that smallpox vaccine only confers protection against the deadly virus for 10 years, but a new study released on Wed 28 Aug 2002 [published in the current issue of The New England Journal of Medicine] found evidence that people may be covered [protected] for 35 years or more, which could mean many Americans retain some level of immunity.
Routine smallpox vaccinations were halted in the United States in 1972. Given the [accepted] 10-year limit of protection, it was assumed that immunity had long ago worn off and everybody was susceptible to the virus. The new study, which involved lab workers who conduct research with smallpox, found that their immune systems show signs of significant levels of protection up to 35 years [after vaccination]. This finding could change the strategy for vaccinating against smallpox in the event of a bioterrorist attack, Jeffrey A. Frelinger, Chairman of Microbiology and Immunology in the University of North Carolina School of Medicine and lead author on the study, told United Press International.
If an attack occurs before a full stockpile of vaccine is ready, the new findings suggest it would be prudent to first begin vaccinating those born after routine smallpox vaccination was halted. This group of people in the United States would have no protection at all, whereas those born before 1972 likely still retain some immunity. Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases, told UPI: "That is a moot point because we will have enough vaccine." He noted 155 million doses are available now, more than enough to protect the number of potentially exposed people in the event of a bioterrorist attack.
In the study, Frelinger and a colleague drew blood samples from 4 laboratory workers who had been vaccinated against the virus within the past 5 years, and 9 other lab workers who had been vaccinated between 5 and more than 35 years ago. After exposing the blood samples to the smallpox virus, the researchers found the body's immune system cells exhibited a response indicative of the ability to suppress the virus whether the person had been vaccinated 5 years ago or 35 years ago, Frelinger said. Those vaccinated 35 years ago showed some drop-off in activity but it was only a small decline, he noted. They still had 2/3rds the response of people vaccinated 5 years ago. "We don't know if that is enough to protect people because it is unethical to expose these people to smallpox," he said. "But I would guess based on mouse studies that it probably is sufficient."
Rafi Ahmed, Director of the Vaccine Research Center at Emory University in Atlanta, agreed. "We don't know if these people vaccinated long ago retain protective immunity, but we can be pretty sure that these individuals will do better than unvaccinated people," he told UPI. Ahmed noted the findings are supported by a previous study conducted in the early 1990s that found people had active immune responses to smallpox virus for up to 50 years after vaccination. Frelinger also pointed out that during an outbreak of smallpox in Liverpool, England, in 1902, people who had been vaccinated 50 years previously were protected from death and serious disease. The vaccine being used at that time was essentially the same as the one in use today, so this suggests people may be protected for up to 50 years, he said. If it holds true, it would mean people born as far back as 1942 may retain some protection against the smallpox virus, he said. [Byline: Steve Mitchell] -- ProMED-mail
[The assay of antiviral activity employed measured how well the immune system cells known as CD8 T cells responded when the participants were exposed to vaccinia virus (used as a substitute for virulent smallpox virus). Exposure to vaccinia virus produced a strong CD8 T-cell response in people who had been vaccinated in recent years, and the response was still considerable in people who had been vaccinated 5 to 35 years previously. Even those who had been vaccinated more than 35 years previously still had a considerable immune response. In recently vaccinated people, about 6.5 percent of CD8 T cells were activated in response to exposure to vaccinia virus, compared with 4 percent in people vaccinated 35 or more years before. This level of response was considered by the North Carolina workers to represent a substantial level of immunity.
The extent to which cell-mediated immunity induced by vaccinia virus (the vaccine virus) to infection by variola (smallpox) virus cannot be measured. Consequently the observations must be interpreted with caution. Furthermore, the numbers of individuals involved is too small to allow estimation of the range of responses that might be expected in the general population. - Mod.CP]
[2] Date: Thu 29 Aug 2002
Source: The New York Times, Thu 29 Aug 2002 [edited]
Value of Duration of Immunity Experiments Questioned
-----------------------------------------------
Scientists at the University of North Carolina have reported additional evidence suggesting that immunity conferred by smallpox vaccine may last longer than had been thought, at least for some people. But they and other researchers cautioned that the findings, from laboratory blood tests, might not apply to people actually exposed to smallpox.
The study, by Dr. Jeffrey A. Frelinger and Dr. Lawal Garba, involved blood samples from 14 individuals; 13 had been vaccinated one to 35 years earlier and one had never been vaccinated. The researchers, who reported their findings in a letter in the 29 Aug 2002 issue of The New England Journal of Medicine, isolated certain white blood cells from each sample. The cells, known as CD-8 T cells, are part of the immune system. The researchers exposed the cells to vaccinia virus, a relative of the smallpox virus used since the 18th century as a smallpox vaccine. The degree to which the immune system cells responded to the virus offers a rough indication of immunity, the researchers said.
The researchers said the participants could not recall how many times they had been vaccinated. Because they worked with the vaccination virus, 4 of the participants in the North Carolina study had last received smallpox vaccinations within 5 years, according to federal guidelines, and 9 others were vaccinated from 6 to 35 years earlier. The researchers said the samples from all 13 vaccinated participants showed a robust immune response. Dr. Frelinger said that he undertook the study because of the scarcity of data on the durability of smallpox vaccination, and that he was surprised to find how durable it was. He acknowledged, however, that his study involved cells and a laboratory dish and said that it remained to be seen what would happen in the event of a real outbreak.
Because smallpox has occurred in the past among people who have been vaccinated, experts have long known that vaccine-conferred immunity wanes over time, but they do not know exactly how much. Dr. Anthony S. Fauci, the Director of the National Institute of Allergy and Infectious Diseases, said that over the years scientists had come up with contradictory findings. Dr. Fauci said his agency was paying for continuing studies that were using similar tests to measure the durability of immunity among people who had received smallpox vaccine.
But other experts said they were not surprised by the North Carolina findings and doubted their usefulness. Old vaccination can protect against death from smallpox and can modify the course of illness. But health officials say they face a more important consideration in preparing for a bioterrorist attack: even a mild case can transmit the smallpox virus and perpetuate an epidemic. "You can't draw conclusions in the real world from the data" from the North Carolina tests, said Dr. Frank Fenner of the University of Canberra in Australia. Dr. D. A. Henderson, who led the health organization's smallpox eradication effort and who is now a top government adviser on bioterrorism, said he had "no idea" how the new findings correlated with protection against natural exposure to smallpox. Dr. Henderson said it was "perfectly obvious that one successful vaccination does not protect for a lifetime." Health officials once recommended smallpox vaccination every 3 years for travelers to infected areas. "It would be foolhardy to rely on any vaccination more than 3 years old as solid protection," said Dr. J. Donald Millar, a former head of the smallpox eradication program at the Centers for Disease Control and Prevention.
Because scientists did not determine the length of protection from a smallpox vaccination before the disease was eradicated, health officials can only extrapolate from information collected from past epidemics, some as long ago as a century. A study of 1163 cases of smallpox in Liverpool, England, in 1902 and 1903 showed a striking difference between vaccinated and unvaccinated patients in all age groups, both in terms of severity of infection and risk of death. Protection waned as time passed from the last vaccination, but was significant even among those 50 and older, most of whom had been vaccinated in childhood. In 1972, Dr. Thomas Mack confirmed the Liverpool findings in a study of 680 cases of smallpox imported into Europe and Canada from 1950 through 1971. Dr. Mack, a preventive-medicine expert who now works at the University of Southern California, found that the death rate was 52 percent among unvaccinated individuals, 1.4 percent among those vaccinated one to 10 years before exposure, 7 percent among those vaccinated 11 to 20 years before exposure, and 11 percent among those vaccinated more than 20 years before exposure.
[Byline: Lawrence K. Altman]
[Let ́s not get carried away by enthusiasm for this new finding, but let's not discount it either. If there is significant protection against death, that at least is something. And I think D. A. Henderson ́s remark must have been quoted out of context -- one shot of the vaccine against another virus, yellow fever, does protect for a lifetime. - Mod.JW]