Any infectious agents or toxic chemical could in theory be engineered for deliberate use as a weapon. Experts in this field believe that smallpox, anthrax, botulism and plague are the pathogens most likely to be used. However, most if not all outbreaks of infectious disease whether natural or deliberate, would quickly be detected by the Global Outbreak Alert and Response Network, which continually monitors reports and rumors of disease events around the world.

Treatment would depend on the particular pathogen or chemical identified as the source of the outbreak. There are recommended strategies to contain natural or deliberate disease and chemical events. WHO has standard operating procedures for treating and containing outbreaks of all known infectious disease. In some cases, isolation of patients, containment of infection and the provision of accurate public information is the most effective strategy.

WHO standard operating protocols indicate when widespread vaccination is appropriate. After any vaccination is given, a certain length of time is required before immunity develops. It may therefore not be effective to vaccinate people who have already been exposed to infection. Containment of infection is therefore extremely important, as is the checking of all contacts an infected person has had with others, in order to ensure they can be treated and infection contained.

At the moment, there are naturally occurring infectious diseases - particularly childhood illnesses - which are causing large numbers of death and widespread illness. People should be routinely vaccinated against these diseases. WHO is currently working to confirm where stores of vaccine are held against some of the pathogens that could potentially be released deliberately. WHO is also encouraging both governments and manufacturers to ensure that adequate stocks are available.

Countries should have contingency plans to cope with any naturally occurring or deliberate outbreak of infectious disease. They should be aware of the international guidance published by WHO. The most important response to any outbreak is a public health response to ensure the safety and treatment of people who could potentially be exposed to a dangerous pathogen. This should include investigating stocks of both drugs and vaccines to ensure that adequate supplies are available to deal with any natural or deliberate outbreak. Countries should also be developing multi-sectoral approaches to dealing with any outbreak of infectious disease. This might include planners from ministries of health, defense, agriculture and the interior.

Pharmaceutical companies and laboratories able to produce vaccine should be contacted by public health authorities and made aware of the potential needs. However, it must be remembered that production on a large scale is usually only possible once a confirmed market is available.

National and international institutions must work together to strengthen the public health infrastructure, including specialist laboratories and epidemiologists. Investment in the public health system is the best possible defense against any outbreak of infectious disease, whether natural or deliberate.