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Monday, March 03, 2003

Health

The Smallpox Vaccination Policy


Since September 11, 2001, biological terrorism has dominated the American public-health agenda. Smallpox was declared eradicated from the globe in 1980. By 1984, only the Centers for Disease Control and Prevention (CDC) in Atlanta and the Research Institute of Viral Preparations in Moscow retained smallpox virus. In 1994, the Russian smallpox virus samples were moved to the State Research Center of Virology and Biotechnology (the Vektor Institute), in Novosibirsk, Russia. United States and foreign leaders have expressed concern that secret stocks of the virus were acquired from laboratories in the former Soviet Union and might be held by extremist political groups for the purpose of biological terrorism. In response to growing concerns about a possible premeditated release of smallpox, public-health authorities in the US recently recommended that every hospital identify and immunize 50 to 100 healthcare providers who would constitute a “smallpox health care team.” In the event of bioterrorist attack, these teams would treat early victims and manage a massive post-event vaccination effort of the general population aimed at stopping the attack from becoming an epidemic. In this article, we review the disease, the vaccine, and the controversy surrounding the current vaccination policy.

What is smallpox?
Smallpox is a serious disease, although no one in the US has contracted it since 1948. It is caused by variola, a virus that spreads from person to person through close contact. The incubation period (the time between acquiring the virus and developing the illness) lasts approximately two weeks. Patients then develop high fever, headache, backache, and generalized malaise followed by the characteristic rash of smallpox, which usually begins around the mouth, face, and forearms, and spreads to the trunk and legs. The complications from smallpox include blindness and death (in up to 30 percent of infected, unvaccinated patients). Smallpox is transmitted from an infected person once a rash appears. Transmission does not occur during the period of illness preceding the rash. Airborne transmission has rarely been documented; the greatest risk of infection occurs among household members and as a result of close contact with persons with smallpox, especially prolonged, face-to-face exposure. Currently, there is no adequate treatment for smallpox. Control of the disease depends on vaccination and isolation of close contacts. These strategies have been shown to interrupt transmission and prevent epidemics of the disease.

The vaccine
Smallpox vaccine is made from a virus called vaccinia, which is similar to variola, but less harmful. The vaccine does not contain smallpox virus, and it can protect people from smallpox. About 95 percent of people will be protected from infection if they receive the vaccine prior to exposure. Getting the vaccine within three days of exposure can prevent the disease or at least make it less severe. Protection from infection lasts three to five years, while protection from severe illness or death can last 10 years or more. The most common side effects of the vaccine include fever, rash, and body aches.

The vaccine also carries the risk of serious adverse reactions that include severe skin reactions, brain swelling (encephalitis), and, in the worst case, death. The best estimates of risk are: 15 per million people vaccinated (0.0015 percent) for severe skin reactions; 3-5 per million people vaccinated (0.0003-.0005 percent) for brain swelling; and 1 per million people vaccinated (0.0001 percent) for death. Five groups are considered high-risk for vaccine complications: (1) persons with eczema or other skin diseases; (2) patients with leukemia, lymphoma, or other cancers who are receiving chemotherapy, radiation therapy, or large doses of steroid medications; (3) patients with HIV infection; (4) pregnant women; and (5) persons with other hereditary problems of the immune system.

The controversy
The development of a vaccination policy depends on a clear understanding of risks and benefits. This is especially problematic in the case of smallpox. It is impossible to balance the risks and benefits of vaccination against the potential risk from an eradicated infectious disease. No one knows whether the smallpox virus exists outside the two laboratories approved by the World Health Organization, whether it has fallen into the hands of organizations or individuals that will or can use it as a weapon, or whether it can actually be disseminated in a way that would cause mass casualties. Advocates for pre-event vaccination are concerned about the significant potential for transmission of smallpox once the disease has been reintroduced, and they argue that mass vaccination would eliminate the threat of smallpox as an agent of bioterrorism.

Although, as discussed above, smallpox is infectious, most transmissions have occurred from patients with obvious disease. If smallpox were to reemerge, infected people would be visibly sick by the time they were highly infectious, thus easily identified, so that they and their contacts could be quarantined to prevent the disease’s spread. Advocates of pre-event vaccination also doubt the effectiveness of “ring vaccination” because of the possibility of simultaneous attacks on multiple cities. In this approach, people with suspected or confirmed smallpox are isolated, and contacts are traced, vaccinated, and kept under close surveillance, as are the household contacts of those contacts. The plan also identifies other high-risk people who may have had direct or indirect contact with the patients and should therefore also be vaccinated. (Imagine rings of containment around the initial infected patient.) Local quarantine and travel restrictions may be enforced if deemed appropriate. The plan does not recommend mass vaccination either in response to documented cases of smallpox or in anticipation of a potential outbreak. Ring vaccination successfully contained outbreaks of smallpox during the worldwide eradication program.

There are concerns about the potential effectiveness of ring vaccination in today’s world. Since we are largely a population without any immunity to smallpox and are highly mobile compared to previous generations, epidemic control after multiple simultaneous exposures may pose significant logistical challenges. The administration of millions of doses of vaccine and effective quarantine during a crisis may be extremely difficult. Nevertheless, any vaccination strategy must consider the risk of adverse events. In the absence of smallpox anywhere in the world, the overriding concern must be first to do no harm. The health status of the US and other developed countries has changed in the 30 years since routine smallpox vaccination ended. The prevalence of disorders that cause immune-system suppression such as HIV, as well as technologies to treat cancer and organ failure, has increased. This has produced a greater number of people who are potentially susceptible to adverse reactions to smallpox vaccination.

Two recent articles in The New England Journal of Medicine attempted to shed light on some of these questions. The first estimated the effects of various vaccination policies in the event of hypothetical smallpox attacks. Vaccination of the public before such an attack would cause about 500 deaths. A highly successful airport attack, in which terrorists developed effective ways to aerosolize the virus, could result in about 50,000 deaths, most of which could be averted by prior vaccination. The study concluded that smallpox vaccination would save lives only if the probability of an attack were substantial.

The second study was a national survey that revealed that the American public is not well informed about smallpox. The majority mistakenly believes that a treatment is available for the disease and that there have been cases of smallpox within the past year. Most respondents stated that they would not agree to vaccination if physicians declined it.

Finally, I and other colleagues at the Children’s Hospital of Philadelphia and University of Pennsylvania conducted a recent survey of emergency healthcare personnel (the same personnel targeted for vaccination under current policy). Preliminary results have been mentioned in the recent Institute of Medicine report on smallpox vaccination and are pending review for publication. We found that over two-thirds of those surveyed favored receiving the pre-event smallpox vaccination, while concern over vaccine-related adverse effects was the most common reason cited to avoid immunization.

In summary, the first phase of the vaccination plan to immunize approximately 500,000 hospital employees is in progress. Many hospitals and medical centers, including my institution, have opted not to participate in this voluntary program at this time given currently available information. Ongoing assessment of the risks of smallpox as an agent of bioterrorism, the development of newer, safer smallpox vaccines, and improved public-health educational efforts are clearly necessary.

Theoklis Zaoutis is attending physician in special immunology (pediatric HIV) at the Children’s Hospital of Philadelphia and an investigator for the Pediatric AIDS Clinical Trials Group (PACTG). He is also a fellow in pediatric infectious diseases at the Children’s Hospital of Philadelphia and an instructor in the department of pediatrics at the University of Pennsylvania School of Medicine.
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