Smallpox: Technical Background on the Disease and Its Potential Role in Terrorism
Released: 2003-01-10T00:00:00

RS21288 -- Smallpox: Technical Background on the Disease and Its Potential Role in Terrorism

Updated January 10, 2003

Smallpox Virus

Viruses are essentially small pieces of genetic material in a protein coat. They cannot reproduce by themselves. To multiply, a virus must hijack the replicationmachinery in living cells by infecting another organism. Smallpox is caused by the Variola virus, which undernormal circumstances only infects human cells. There are two types of Variola viruses. Variola minor causes a relatively mild disease that has less thana 1% fatality rate. Variola major causes what isgenerally thought of as smallpox, a very severe illness with a fatality rate of approximately 30%. (1) These viruses are part of the Orthopox genus whichalsocontains the viruses responsible for vaccinia, monkeypox, cowpox, camelpox and mousepox. (2)

Smallpox Disease

Before the last reported case of smallpox (a result of a laboratory accident in England in 1978), smallpox was considered to be one of the worst scourges inhuman history. Smallpox is estimated to have killed between 300 and 500 million people in the twentieth centuryalone.

Once infected, the victim incubates the virus for seven to seventeen days during which the victim feels and appears normal. This stage is followed by one tofour days of high fever, malaise, headache, and muscle ache, often accompanied with nausea and vomiting. Duringthis time the person looks and feels very ill,but is not yet contagious. After this stage, the characteristic sores develop; first in the mouth then over the rest ofthe body. If the victim survives, the soresscab over and turn to scars in three to four weeks. About 30% of unvaccinated victims die (some sources suggestup to 50%). Up to 80% of the survivors aredisfigured by pockmarks or limb deformities.

Smallpox is contagious, but the Centers for Disease Control and Prevention (CDC) (3) considers it to spread less widely and less rapidly than chickenpox,measles, whooping cough, or influenza. The victim is most likely to infect other people when the sores in the mouthare most active. This is in the first weekof the rash when virus comes out of the sores and into the saliva where they are easily aerosolized by coughing orsneezing. Although smallpox is usuallytransmitted by face to face contact, it can also be transmitted through the air over dozens of feet and by contaminatedclothing or bedding.

Smallpox Vaccine

The vaccine works by infecting a person with vaccinia virus which is closely related to smallpox virus. (4) The vaccine triggers immunity against all closelyrelated viruses, including smallpox. This immunity decreases over time; however, people who contract smallpoxeven thirty years after vaccination are muchless likely to die than unvaccinated people. (5) Interestingly, the vaccine also helps reduce the severity of the disease if given to victims within a few days aftersmallpox exposure. This is the only known treatment for smallpox, although several antiviral drugs have shownpromise in preliminary laboratory studies.

Although the vaccinia vaccine is very effective at preventing smallpox, it is not without risks. Its complication rate is higher than that associated with anyroutinely used vaccine. Based on historical experience, experts estimate that most vaccinees will experience onlymild side effects such as low-grade fever, but1 in 797 people will experience serious side effects. Table 1 describes the historical complicationrates.

Table 1. Historical smallpox vaccine complication rates (cases/million vaccinations)

Source: CDC, Morbidity and Mortality Weekly Report, June 22, 2001, Vol. 50, No. RR-10, p.8.

Inadvertent inoculation is the spread of the usually localized vaccinia infection to other parts of the body, causing sores and scarring most commonly on theface, genitals, and rectum. Generalized vaccinia causes vaccinia sores over the entire body. Eczema vaccinatumis a sometime fatal skin infection in peoplewho have a skin disorder such as eczema or atopic dermatitis. Encephalitis is a very serious and sometimes fatalinflammation of the brain. Progressivevaccinia is an inexorable rotting away of the flesh around the vaccine site that can sometimes also be fatal. As aresult of these complications, experts project1-2 deaths per million vaccinations.

Complications are not limited to people who get vaccinated. People who come into contact with those who have been vaccinated within two weeks may also beexposed to the live vaccinia virus and develop complications. Some experts estimate that up to 20% of thecomplications will occur in the unvaccinatedcontacts. Historically, for every million people vaccinated, about 65 people who were not vaccinated becameinfected and developed a serious complicationsimply by coming into contact with a vaccinee. (6) Because of the high rate of vaccine complications, in 1971, U.S. public health authorities rescinded therecommendation for universal domestic smallpox vaccination.

It is likely that the numbers in Table 1 underestimate the current and future problem with the vaccine. Since these numbers were last compiled in 1968, thenumber of people predisposed to problems with the vaccine has increased. Some experts estimate that up to 25%of the population now have conditions thatwould make vaccination contraindicated. These conditions include a history of eczema or other exfoliative skindisorder, pregnancy, or any immunodeficiencywhich could be caused by AIDS, chemotherapy or anti-rejection drugs following organ transplant. Because of theserious risk of transferring the virus to ahousehold member, it is recommended that people who live with someone with one of the above conditions notreceive the vaccine. Excluding these people iscomplicated by the large number of people who are unaware that they have a disease that will produce a serious sideeffect. For example, a vaccinee could livewith one of the estimated 300,000 people in the United States that do not know they are HIV positive.

The only product proven to counter some of the vaccine complications is vaccinia immunoglobulin (VIG). This is extracted from the blood of peoplevaccinated with the smallpox vaccine. It is only effective for treatment of eczema vaccinatum and certain cases ofprogressive vaccinia. Significantly, VIGprovides no benefit in the treatment of postvaccinial encephalitis. Current civilian supplies of VIG are controlledby the CDC and are estimated to be enough todeal with the complications from about 27 million vaccinations. The CDC is in the process of procuring more VIG. Because the antiviral drug cidofovir hasshown some anti-vaccinia activity in lab animals, it is available for use as an Investigational New Drug when VIGtreatment fails.

Threat of Terrorist Use

Although smallpox was officially declared to have been eliminated from the wild in 1980, many countries maintained laboratory stocks of the virus obtainedduring outbreaks. By 1985, these stocks were supposed to have been destroyed or transferred to one of the officialrepositories; one in the Soviet Union and theother in the United States.

Russia inherited the smallpox stewardship following the break up of the Soviet Union. Although only the United States and Russia have declared stocks ofsmallpox, some experts have stated that although very unlikely, it is possible that some other countries haveundeclared stocks. Countries that may havedeliberately or inadvertently retained smallpox virus from naturally occurring outbreaks before eradication include:China, Cuba, India, Iran, Iraq, Israel, NorthKorea, Pakistan, and Yugoslavia. (7) A November2002 CIA intelligence review added France to this list and reportedly states a "high, but not very high [levelof] confidence" that Iraq and France have live smallpox samples and a "medium" level of confidence that NorthKorea does. (8)

The highest barrier to a non-state sponsored terrorist using smallpox is likely to be the difficulty in obtaining the virus in the first place. Because all countrieshave stopped smallpox vaccination programs, citizens of all countries are equally vulnerable to a spreadingepidemic. Therefore, it is in the best interest of acountry with even an undeclared smallpox stock to keep it very secure. Despite this, some fear that the Russianstocks may not be sufficiently secure due to theeconomic collapse that accompanied the break up of the Soviet Union.

Other than from a government controlled stockpile, some have suggested that it may be possible to acquire the virus from the bodies of smallpox victims buriedin the Siberian permafrost in the 1800s. However, this is probably unlikely since Russian experts have been unableto acquire viable virus this way despitemultiple attempts. (9) In 2002, American scientistssuccessfully constructed infectious polio virus from mail-ordered pieces of DNA. (10) However, most expertsclaim that it would be very difficult to construct Variola virus in this manner. For more information on this topic,see CRS Report RS21369(pdf) SyntheticPoliovirus: Bioterrorism and Science Policy Implications .

If a terrorist organization were able to obtain a sample of virus, it would also need the advanced technical knowledge, skill and facilities to maintain the viruswithout infecting themselves until the planned dissemination. It is considered to be quite difficult to "weaponize"smallpox. (11) However, in general,weaponization refers to developing advanced delivery systems such as missiles, artillery, or bombs to cause masscasualties. This technological barrier wouldbe much lower for a terrorist. A terrorist, who was not concerned with his own survival could potentially use hisown body as the delivery system, infectingdozens of people before succumbing to the disease.

In addition to the threat posed by terrorist groups, it is possible that another nation may choose to use smallpox against the United States. Some experts suggestthat of the countries that might have undeclared stocks of smallpox virus, Iraq may pose the most danger to theUnited States. Some experts believe that it isvery unlikely that Iraq has smallpox since they did not use it during the Gulf War. However, those who feel thatIraq has the smallpox virus counter that itwould not have been used because it is not well suited for battlefield deployment since it is contagious and likelyto infect troops on both sides. Some expertsalso believe that Iraq was dissuaded from using chemical or biological weapons by what could have been interpretedas a thinly veiled threat of nuclearretaliation. (12) In the current situation of risingtensions, some experts have stated that if Iraq has the capability, Saddam Hussein may unleash smallpox as aweapon of last resort, particularly if he can deploy it covertly on United States soil. (13) In December 2002, the Administration reserved the right to use nuclearweapons to respond to the use of weapons of mass destruction against the United States or its allies. (14)

Nonetheless, most experts feel that the barriers posed by acquisition and successful deployment of smallpox virus are high enough to make such an attack veryunlikely. Furthermore because of these hurdles, most experts feel that a terrorist organization would require a statesponsor in order to successfully obtain anddeploy smallpox.

Policy Implications

Although most experts deem the risk of a smallpox attack to be very low, the high consequences of a release have led the President to order the vaccination ofapproximately 500,000 people in the armed forces and to initiate a voluntary program to encourage as many as 10million medical workers and first respondersto be vaccinated. By the middle of 2003, the vaccine will be available on demand to any American adult who is notin a high-risk group for complications. However, the Administration will not recommend vaccination for members of the general public because of the highcomplication rate. (15)

Scientific research may be able to further limit the threat posed by smallpox. If a safer smallpox vaccine could be produced, for instance, public health officialswould be less reluctant to recommend mass vaccination. The development of such a vaccine is stymied by severalfactors. One is that it is difficult to predictbefore making a large investment whether a new vaccine will be safer and still effective against smallpox. (16) Another factor is the uncertain market of atherapeutic agent that is designed to protect against what most experts agree is a very unlikely event. Without aguaranteed market, the commercial sector maybe reluctant to make such investments.

Some experts suggest that, in general, it may be better to develop treatments rather than relying on prophylactic measures for the many potential biologicalagents that could be used to attack the United States. They suggest that the financial and societal costs of multiplemass vaccination programs may make avaccines-only approach impractical. Some scientists are working on producing antiviral drugs as a cure forsmallpox and several have shown promise inpreliminary studies. (17) However, more work needsto be done to improve animal models of smallpox so that the efficacy of new therapeutics can be tested. (18) Another potential advantage of this approach is that these drugs may be effective against other viruses and thereforemight be marketable as treatments forinfluenza or AIDS.

The United States might be better equipped to defend against a smallpox attack if the status of any undeclared smallpox stocks could be determined with greatercertainty. For example, if it could be determined that Iraq does not have any smallpox then focus could be shiftedto preventing terrorist access to other sources. Unfortunately, it is possible that Iraq could successfully hide a smallpox program from any inspection regime.

The United States is helping to increase the security of the former Soviet Union's biological weapon stockpiles. By focusing on the physical security of theagents and the economic security of the scientists, these programs simultaneously reduce the threat posed by all ofthe agents in the former Soviet Union'sarsenal. For a comprehensive discussion of these programs, see CRS Report RL31368(pdf) PreventingProliferation of Biological Weapons: U.S. Assistance to theFormer Soviet States .