On December 13, 2002, President Bush announced the National Smallpox Immunization Plan (NSIP) to immunize health care workers who might have to respond to patients affected by an outbreak of smallpox. This plan is designed to help local and state authorities in planning and preparedness by providing vaccine to approximately 500,000 individuals. This program is voluntary and is structured to provide a cadre of first responders in the event of the return of smallpox as a health threat. Not since the end of the compulsory smallpox vaccination campaign in 1972 has the general public been offered this vaccine. As of May 9, 2003, a total of 36,217 civilian health care workers had been vacci-nated.

THE VACCINE

The live-virus vaccine is made from a virus that is similar to smallpox called vaccinia. This lyophilized product contains the vaccinia virus, prepared from calf lymph (Dryvax®, Wyeth Laboratories). It is packaged in 100-dose vials along with diluent and bifurcated needles. The vaccine does not contain smallpox virus (variola) and cannot produce the clinical disease smallpox.

The vaccine is introduced by means of a bifurcated needle that is designed to deliver 107 to 108 plaque-forming units of undiluted vaccine via three to 15 punctures into the skin. Two to three punctures are recommended for people undergoing primary vaccination, whereas up to 15 punctures may be required to ensure an adequate challenge in those who are undergoing revaccination. Only a few drops of blood should be visible at the inoculation site after the vaccination.

Because the vaccine contains a “live” virus, which is capable of viral replication after it is inoculated into the appropriate cell, special care must be taken to prevent inadvertent spread from the vaccination site. Appropriate hand hygiene, combined with a gauze dressing and a semipermeable membrane, is recommended to prevent secondary spread.

A successful vaccination is defined as the formation of a vesicle at the site seven to nine days after the introduction of the vaccine (viral “take”). In uncomplicated vaccinations, the vesicle progresses through pustule formation, ulceration, and eventual scab formation over the ensuing three weeks (Figure 1). The scab is allowed to separate, and a small scar remains at the site of vaccination. Evidence of neutralizing antibody and cell-mediated immunity can be detected within eight to nine days of the vaccination. levitra tablets

Figure 1 Smallpox series

Figure 1 Smallpox series.

Mild, transient reactions are not uncommon among vaccine recipients. Beginning five to seven days after vaccination, pain at the inoculation site, local swelling, redness, and lymphadenopathy are all usual responses. A generalized erythematous eruption occurring with the onset of a fever is also common. This “flat” rash is not progressive and is not contagious. Medical attention is rarely required, and these reactions usually resolve on their own within one or two days. Fever, if it occurs, is usually mild and short-lived. In one study of responses to the vaccine, a temperature above 101°F was seen in fewer than 10% of recipients.

More serious adverse events have been difficult to quantify. Most of the available data are from studies conducted in the 1960s. These more serious adverse effects include inadvertent inoculation of vaccinia away from the vaccination site, generalized vaccinia, eczema at the site, progressive vaccinia (vaccinia necrosum), encephalitis, and, rarely, death (Table 1).

Table 1 Rates of Adverse Reactions to Smallpox Vaccine per Million Doses

Adverse Event 1968
Inadvertent inoculation 529
Generalized vaccinia 242
Eczema vaccinatum 10-39
Vaccinia necrosum 1-2
Postvaccinial encephalitis 3-12
Death 1-2
Data adapted from Lane M,et al.N Engl J Med 1969;281:1201-1208;5 and Lane M, et al.J Infect Dis 1970;122:303-309.6

The rates of occurrence of these events can vary significantly in today’s nonimmunized population. Furthermore, the increased number of people with immune suppression from cancer, cancer chemotherapy, organ transplantation, and other illnesses such as human immunodeficiency virus (HIV) infection can produce a greater risk of such events. Conversely, those who have previously been vaccinated may be at lower risk for these adverse events.
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During the current vaccination campaign, statistics on adverse events are being collected from civilian vaccinations and from more than 449,198 vaccinations performed for military personnel to date. Most of these vaccinations have been primary. As of May 9, 2003, no cases of serious adverse events had been reported. However, an increased number of episodes of myopericarditis have been recognized among civilian and military personnel, who have constituted the majority of primary vaccinees. These cases have been temporally related to smallpox vaccination, but a causative link has not been established. Military personnel may receive a number of concurrent vaccines. Among civilian health care workers, 30 cardiac adverse events have been reported, including 21 cases of myo-pericarditis, nine myocardial ischemic events (six people with myocardial infarction and three with angina), and two deaths. All of the individuals who died had known cardiac risk factors and no evidence of myopericarditis at autopsy. The death rate is no greater than that expected among persons in these age groups in the general population.

Two medications are available for the treatment of severe adverse reactions to the smallpox vaccine. Vaccinia immune globulin (VIG) has been used in the past for the treatment of these more serious adverse events, but supplies are limited. It is available from the Centers for Disease Control and Prevention (CDC) only under Investigational New Drug (IND) protocols. To date, no VIG has been required for civilian vaccinees. Cidofovir (Vistide®, Gilead), a potent antiviral agent approved for the treatment of cytomegalovirus retinitis, has also shown activity against pox viruses and is available under IND protocol from the CDC. suhagra

Table 2 Contraindications to Smallpox Vaccine

• History or presence of eczema, atopic dermatitis, or
other exfoliative skin conditions in individuals and their
household contacts
• Conditions associated with immunosuppression, includ-
ing human immunodeficiency virus infection
• Pregnancy or breast-feeding
• Significant cardiac disease
• Age younger than one year
• Serious allergy to any vaccine component

Because of the possibility of increased rates of adverse events among these potential vaccine recipients, the Advisory Committee on Immunization Practices (ACIP) and the Healthcare Infection Control Practices Advisory Committee (HIC-PAC) have issued recommendations for those in whom the smallpox vaccine would be contraindicated (Table 2). The recent identification of cardiac adverse events has prompted the ACIP to include in the screening persons with recognized risk factors for cardiac disease, such as the following:

•    known underlying heart disease, regardless of symptoms

•  three or more major cardiac risk factors (e.g., hypertension, hypercholesterolemia, diabetes, a history of smoking, or a first-degree relative with heart disease before age 50 years)
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Individuals with these conditions and those who are in contact with others with these conditions in the household should refrain from voluntary pre-event vaccination programs.

Category: Drugs / Tags: Smallpox Vaccine

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