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Possible Adverse Effects Are Also Discussed
June 23, 2003 — Despite concerns about the safety of a large-scale smallpox vaccination program, new research from the U.S. military suggests that such a program can be carried out safely, with relatively few serious adverse events, according to an article in the June 25 issue of The Journal of the American Medical Association.
According to background information in the article, in December 2002 the United States implemented a program of smallpox vaccinations for approximately 500,000 military personnel in a national program of preparedness against use of smallpox as a biological weapon. Pre-attack vaccination was determined to be the best way to personally protect troops so they can continue their missions.
The resumption of smallpox vaccinations raises important questions regarding implementation and safety. John D. Grabenstein, R.Ph., Ph.D., of the Military Vaccine Agency, U.S. Army Medical Command, Falls Church, Va., and William Winkenwerder, Jr., M.D., M.B.A., Assistant Secretary of Defense, Pentagon, Washington, D.C., analyzed data from the U.S. military smallpox vaccination program from its inception on December 13, 2002, through May 28, 2003. The researchers looked at the number of vaccinations, rates of vaccination exemptions, symptoms, and adverse events. Data were collected via reports to headquarters of U.S. Department of Defense (DoD) fixed and field medical treatment facilities on multiple continents and ships at sea. In 5.5 months, the DoD administered 450,293 smallpox vaccinations (70.5 percent primary vaccinees and 29.5 percent revaccinees).
"In two settings, 0.5 percent and 3.0 percent of vaccine recipients needed short-term sick leave. Most adverse events occurred at rates below historical rates. One case of encephalitis and 37 cases of acute myopericarditis developed after vaccination; all cases recovered," they write. "Program implementation emphasized human factors: Careful staff training, contraindication screening, recipient education, and attention to bandaging. Our experience suggests that broad smallpox vaccination programs may be implemented with fewer serious adverse events than previously believed," the authors conclude.
Related Article: Diluted Vaccine Works On Those Previously Vaccinated
Since smallpox vaccine has not been widely used in the United States since 1972, it was anticipated that many previously vaccinated persons would exhibit a major reaction to smallpox vaccine. The study included 80 non-naive participants, randomized to receive either undiluted or diluted (1:3.2, 1:10, or 1:32) doses of smallpox vaccine. A comparison group of 10 vaccinia-naive participants received undiluted vaccine.
Participants were enrolled between April 1 and May 15, 2002, and examined for major reactions, which were defined as a vesicular or pustular lesion of the skin or an area of palpable induration surrounding a central lesion following vaccination and measures of viral shedding and antibody titers. Initial vaccination resulted in a major reaction in 64 of 80 participants in the previously vaccinated groups.
"Ninety-five percent of non-naive participants had major reactions in the undiluted group, 90 percent in the 1:3.2 dilution group, 81 percent in the 1:10 dilution group, and 52.6 percent in the 1:32 dilution group. All (n = 10) of the vaccinia-naive participants had major reactions. Compared with vaccinia-naive participants, non-naive participants had significantly smaller skin lesions and significantly less incidence of fever. Pre-existing antibody was present in 76 of 80 non-naive participants. Antibody responses were significantly higher and occurred more rapidly in the non-naive participants compared with the vaccinia-naive participants," the researchers write.
"Previously vaccinated persons can be successfully revaccinated with diluted (equal or less than 1:10) smallpox vaccine. Fewer adverse reactions were observed in this study of non-naive participants when compared with events in vaccinia-naive participants, which was probably due to immunologic memory," the authors conclude.
Certain Type of Skin Rash Is Common Following Vaccination
Also reported in this issue of JAMA, a small proportion of persons who are vaccinated for smallpox contract folliculitis, a benign skin rash, according to Thomas R. Talbot, M.D., and colleagues from Vanderbilt University School of Medicine, Nashville, Tenn. The researchers conducted a study to examine the skin eruptions following smallpox vaccination in healthy, vaccinia-naive (not previously vaccinated) adult participants, from October 2002 to March 2003.
In previous reports, serious skin rashes directly related to the vaccinia virus have occurred following smallpox vaccination, but other less severe rashes are possible and distinguishing the serious rashes from the less serious ones is important. During the trial, of 148 volunteers, four (2.7 percent) participants developed generalized skin eruptions and 11 (7.4 percent) noted focal skin eruptions. Viral cultures of sample lesions were negative for vaccinia. The result of a skin biopsy sample from one case of generalized rash revealed suppurative folliculitis without evidence of viral infection. All lesions resolved without scarring.
"While folliculitis following vaccination resolved fully in our volunteers, required no specific interventions, and showed no apparent residual sequelae, the concern caused by this eruption on the part of the participants and the clinicians was substantial. The potential for misinformation and concern about skin eruptions following smallpox vaccination are important issues. It is hoped that this report will help educate clinicians, reduce anxiety, and provide reassurance to the medical community," the researchers conclude.
Heart Ailment Is A Possible Adverse Event From Vaccination
Myopericarditis, which involves the inflammation of the heart muscle or sac surrounding the heart, should be an expected but apparently uncommon adverse event associated with smallpox vaccination, according to an article in this issue of JAMA by Jeffrey S. Halsell, D.O., James R. Riddle, D.V.M., M.P.H., and members of the Department of Defense Smallpox Vaccination Clinical Evaluation Team.
The researchers report on the first 18 cases of probable myopericarditis following smallpox vaccination among otherwise healthy, young adult members of the U.S. military who were vaccinated between mid-December 2002 and March 14, 2003. Despite decades as the standard vaccine for U.S. civilian and military populations, the New York City Board of Health (NYCBOH) strain of vaccinia virus (Dryvax, Wyeth Laboratories, Marietta, Pa.) has only rarely been associated with myopericarditis following vaccination. Only 4 cases were reported in the medical literature between 1955 and 1986.
Among 230,734 primary vaccinees, 18 cases of probable myopericarditis after smallpox vaccination were reported (an incidence of 7.8 per 100,000 over 30 days; one per 12,819). No cases of myopericarditis following smallpox vaccination were reported among 95,622 vaccinees who were previously vaccinated.
"Based on reports of cardiac events following smallpox vaccination among military and civilian vaccinees, the CDC has recommended additional exemptions based on known cardiac disease or potential risk factors for cardiac disease. These findings are relevant to current policies and guidelines for vaccinating military and civilian populations against smallpox. Although these cases all recovered clinically from their acute illness, the potential long-term consequences must be evaluated to know the true significance of myopericarditis following vaccination.
"Furthermore, these findings suggest that myopericarditis following smallpox vaccination is an expected adverse event. We project a morbidity estimate of at least 78 clinical myopericarditis cases per million primary vaccinees in comparable adult populations. Myopericarditis following vaccination should be considered in the differential diagnosis of patients with chest pain four to 30 days following smallpox vaccination," the authors conclude.
Editorial: Smallpox Immunization in the 21st Century — The Old and the New
In an accompanying editorial, Mary E. Wright, M.D., M.P.H., and Anthony S. Fauci, M.D., of the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, Md., write that the four reports in this issue of The Journal highlight the ongoing challenge to clinicians to be mindful of the old while being vigilant for the new.
"Before 2002, virtually all that was known about the efficacy and safety of smallpox vaccination had been documented in studies conducted a minimum of 30 years earlier. This was an era prior to the availability of technological advances, such as flow cytometry, polymerase chain reaction, and magnetic resonance imaging and before modern-day computer systems made it possible to perform diagnostic surveillance and statistical analyses in close to real time. The continued application of these and other new technologies to this historic public health issue should be of great value in furthering the understanding of the nature of smallpox protection induced by vaccination," they write.
"By rapidly sharing the data from their smallpox vaccination experience with the general medical community, the Department of Defense has provided the civilian population with critical information pertaining to an important general public health issue and should be commended for this effort. This is a model for how military and civilian cooperation can effectively serve the public health of the entire nation," they authors conclude.