| Smallpox vaccine
Public health strategies
On 8 May 1980, during the Thirty-Third World Health
Assembly, smallpox was declared to have been eradicated. Small stocks of the virus
remained in secure laboratories and some other laboratories were allowed to maintain
stocks of up to 20% of the genome sequence for the purpose of international research. An
emergency stock of smallpox vaccine (vaccinia) was kept in deep freeze in certain
locations. No vaccination of populations has been carried out since eradication was
declared. However, vaccination has continued for at-risk laboratory workers and other
persons working with vaccinia virus that is not highly attenuated, recombinant vaccinia
viruses derived from vaccinia strains that are not highly attenuated, or other non-variola
orthopoxviruses (e.g. monkeypox), as well as for certain military personnel.
WHO perspective
No vaccine is currently available for widespread use. WHO
maintains a web site with latest
information.
Special issues
Bioterrorism Intermittent discussions have
continued since the 1980s about the potential threat of the use of smallpox as a terrorist
weapon. Governments have recently begun to seriously consider whether the vaccine should
be available for widespread use. New smallpox vaccines are being developed as a
contingency for the protection of civilian and military personnel against the deliberate
dissemination of the smallpox virus by terrorists. WHO has not made any recommendation
about the use of the vaccine in this new environment, but it remains for each country to
conduct a risk assessment vis-à-vis its own population. At present the risk of smallpox
virus being used for terrorist purposes appears to be extremely low in most countries.
During the smallpox eradication programme, targeted
vaccination of close contacts played the most important role in preventing the spread of
the disease and assured the administration of vaccine to those at greatest risk. This was
sometimes supplemented with broader vaccination campaigns if there were large numbers of
cases in a community. If contacts are vaccinated within four days of exposure they may be
protected or at least develop less severe disease than would otherwise be the case.
Adverse reactions: The live viral vaccine caused
rare but serious adverse reactions, especially in persons with deficiencies of the immune
system, and common local reactions. The complications arising from smallpox vaccination
have been well documented. The consequences of inadvertent inoculation at other sites, and
skin and central nervous system disorders, were the most frequently recognized adverse
events. Dermal complications included vaccinia necrosum, eczema vaccinatum,
generalized vaccinia and erythematous urticarial eruptions. The highest risk for death in
infants was attributed to post-vaccination encephalitis. Persons should only be
vaccinated, therefore, who have the greatest risk of disease. Contagious individuals and
contacts who develop fever should be isolated from non-vaccinated persons. Smallpox
vaccine should not be administered to pregnant women for routine non-emergency
indications. However, the risk of developing complications attributable to the vaccine is
outweighed by that of developing smallpox in close contacts.
Duration of protection: Epidemiological studies
have demonstrated that vaccination protects against smallpox for less than five years
after primary vaccination and that substantial but waning immunity can persist for ten
years or longer. Protection may last longer when revaccination is performed.
Key references
Fenner F, Henderson DA, Arita I, Jezek Z, Ladnyi ID. Smallpox
and its eradication. Geneva: World Health Organization; 1988.
Henderson DA, et al. Smallpox as a biological weapon:
medical and public health management. Journal of the American Medical Association
1999;281(22):2127-37.
Henderson DA. Smallpox: clinical and epidemiologic
features. Emerging Infectious Diseases 1999;5:537-9.
Lublin-Tennenbaum T, Katzenelson E, El-Ad B, Katz E.
Correlation between cutaneous reaction in vaccinees immunized against smallpox and
antibody titer determined by plaque neutralization test and ELISA. Viral Immunology
1990;3:19-25.
Other web sites
CDC Public Health Emergency
Preparedness & Response web site
Useful
Links for Health Effects from Chemical and Biological Agents
WHO:
Anthrax Fact Sheet
WHO: Guidance on Anthrax
WHO: Smallpox FAQ and fact
sheet
WHO: Updated Guidance on
Smallpox Vaccination
WHO:
Responding to deliberate use
WHO: Health Aspects of
Biological and Chemical Weapons
WHO: AMRO/PAHO - Consultation
Meeting on Bioterrorism
US FDA: Bioterrorism
Information
Global Disaster
Information Network
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Updated June 2002 |
