Some responses from the Massachusetts Department of Public Health to recent questions related to smallpox preparedness by Alfred DeMaria, Jr., M.D., Director of the Bureau of Communicable Disease Control and State Epidemiologist.
Q. Does the end of the Iraq War and the Saddam Hussein regime in Iraq mean the end of the threat of smallpox and the imperative to plan for the potential of smallpox as a bioterrorism threat?
A. No. While there was some concern that Iraq had smallpox virus and could release it, the threat of possible smallpox virus possession was never limited to the former Iraqi regime. Plans for smallpox preparedness were developed and completed through the work of the Smallpox Work Group of the Massachusetts Department of Public Health Bioterrorism Preparedness and Response Program Advisory Committee in the summer of 2002, before concrete discussion of war in Iraq and before the President enunciated his ultimatums to Iraq that led to war or announced the federal smallpox plan in December of 2002. Thus, the Massachusetts smallpox plan was developed without reference to Iraq or the war in Iraq and the program was initiated without urgency related to the war. The situation remains that we have no way to assess the risk of smallpox as a bioterrorist weapon. The Massachusetts plan is based on the assumption that some small, but real, threat exists and a minimal number of individuals among several professional disciplines need to be vaccinated to be able to respond to smallpox without significant risk to their lives.
Q. Is there a significant risk of injury and death from smallpox vaccination?
A. Smallpox vaccine does have serious adverse events associated with its use. These must be and have been taken seriously. However, objectively and quantitatively the risk of smallpox vaccination is low, especially in previously vaccinated adults who are carefully screened for risk factors for adverse events.
Data from the 1960s have been used to guide risk assessment, but these data have limitations that under-estimate some risks, as demonstrated by the new appreciation of the risk of myocarditis and myopericarditis generated by the military and civilian vaccination programs, but over-estimate others. Another limitation of historical data occurs when all vaccinees are aggregated. When analyzed by excluding people being screened out of the current program, the rates of adverse events are two to four-fold lower than the overall rates. Most of the possible myocarditis cases being observed in current programs are in the previously unvaccinated.
Rates of adverse events in all studies are low; serious adverse events in the range of less than 100 per thousand, conservatively assessed, or 0.01%, 1 per 10,000. Now we have the accrued, modern experience of the U.S. military and civilian programs. In the military program, with over 450,000 vaccinated, with most vaccinees (70.5%) being not previously vaccinated, there were 38 moderate or severe adverse events (0.008%) and 106 mild or temporary events (0.02%), with no deaths, cases of eczema vaccinatum or progressive vaccinia. All adverse events resolved and only 0.5-3.0% of vaccinees required any sick leave. Among 37,800 civilian vaccinees, there were 71 serious adverse events of any sort following vaccination (0.2%), which may or may not have been related to vaccination. Myopericarditis has become the most frequent serious adverse event, but almost all who develop myopericarditis recover without apparent sequelae. The relationship of other cardiac events with vaccination is unclear. All volunteers are now screened for history of cardiac disease and risk factors before being vaccinated.
Q. Does vaccinating health care workers put patients in danger?
A. Although we must be concerned for transmission of vaccinia virus to patients, especially immune compromised patients, this remains a theoretical risk. The vaccination program provides extensive infection control instruction and a detailed protocol for handling site and dressing, health care workers use impermeable dressings that contain virus and dressings are inspected prior to each shift. There have been no transmissions of vaccine virus from vaccinated health care workers to patients in the experience of vaccinating civilian health care workers in hospitals or at the National Institutes of Health, in the Israeli experience vaccinating over 14,000 health care workers and in the U.S. military experience amounting to more than 19,000 worker-months of clinical contact.
Q. Haven’t public health agencies lost interest in smallpox preparedness involving vaccination?
A. No. The rationale for smallpox vaccination in preparation for the threat of smallpox release as a terrorist act has not changed. In order to be able to ask health care workers and others to respond to smallpox, we need to vaccinate them first. Smallpox is associated with a 50% mortality rate in the never vaccinated. The Massachusetts plan was not implemented with a sense of urgency, but there has been and continues to be determination to achieve the goal of having a sufficient number of professionals from multiple disciplines who can be called upon to respond to smallpox without fear of acquiring the infection.
Q. Doesn’t vaccination within 4 days of exposure to smallpox prevent smallpox?
A. No. Although some people vaccinated after smallpox exposure will escape getting smallpox (as will some people who are not vaccinated), most people vaccinated after smallpox exposure will still get smallpox, although they are very likely to get a milder case and are much less likely to die from smallpox. Persons exposed to smallpox will have to be quarantined or be subject to personal surveillance for the time they may develop smallpox, despite being vaccinated. Persons exposed to smallpox who are vaccinated, but do not have a take, will likely get an unmitigated case of smallpox. Therefore, a response plan that involves vaccination only after exposure will not prevent smallpox, will not avoid the need to quarantine the exposed (and therefore restrict their work and contacts), and, in the small proportion of people who do not have a successful vaccination, will lead to severe and life-threatening disease. On the other hand, there has never been a case of smallpox reported in a smallpox care-giving health care worker who had been vaccinated within seven years of providing that care. Post-exposure vaccination is a critical, life-saving component of disease control in the event of smallpox release, but is not sufficient preparation for responders to smallpox.
Q. Can’t unvaccinated health care workers rely on patient isolation and personal protective equipment to protect them from smallpox?
A. No. Isolation and personal protective equipment are critical to the management of smallpox cases, but may not be sufficient to provide adequate protection for the unvaccinated. There has been no experience in using personal protective equipment in the absence of vaccination as part of prevention of transmission of smallpox. Studies of infection control for smallpox were performed in an era in which the vast majority of people involved in care had been vaccinated and had been exposed to vaccinia virus (an in many cases smallpox) on many occasions (leading to boosting of immunity) and before the modern era of infection control practice. The only airborne infection that has been adequately studied in respect to using personal protective equipment is tuberculosis, and tuberculosis is not as communicable as smallpox and is not transmitted by contact. The current official infection control recommendation is that everyone providing care for cases of smallpox be vaccinated and use isolation and personal protective equipment. Measles and chickenpox, to a degree, are transmitted in the same fashion as smallpox, but health care workers who are susceptible to these viral infections are generally not allowed to care for patients with measles or chickenpox despite personal protective equipment, unless it is unavoidable.
Q. If someone volunteers for smallpox vaccination, will they be forced to work wherever they are sent, including possibly to another hospital or health care facility, anywhere in the state?
A. No. Participation in the vaccination and response program is entirely voluntary. However, the purpose of the program is to have people available to respond to smallpox who are immune to smallpox. Health care and other responders are not being vaccinated because they might be exposed to smallpox (this could happen to anyone should smallpox virus be released), but rather are being vaccinated so that they can be asked to respond to smallpox, should it occur. It is most likely that people will be asked to respond to smallpox within their own professional scope of work and practice, within their own work setting, especially if the goal of having a sufficient number of vaccinated smallpox responders is achieved. However, there is the possibility that people might be asked to respond to smallpox in a setting other than their own usual work setting. This must obviously be voluntary and the cooperation of employers will be necessary, as well.
It should be understood that the existence or transmission of smallpox in the United States would be an event of enormous threat and significance, which would result in significant restrictions in travel and normal activities, and is likely to result in suspension of schools, public events and some businesses. Under those circumstances, many civilians will be called upon to provide the assistance necessary to assure the control of smallpox and vaccinated individuals may be needed to go beyond their usual work setting. If the possibility that you might be asked to make such a commitment in extraordinary, emergency circumstances makes you uncomfortable, then you should not volunteer for smallpox preparedness vaccination.