For approximately 25% of the general population, post-vaccination complications caused by traditional (1st and 2nd generation) smallpox vaccines can be serious (encephalitis, eczema vaccinatum and generalised vaccinia) and in some cases, life-threatening.
Individuals who have any of the following conditions should not be vaccinated with traditional smallpox vaccines:
Eczema or atopic dermatitis (even if the condition is not currently active, mild or experienced as a child)
Skin conditions such as burns, chickenpox, shingles, impetigo, herpes, severe acne, or psoriasis
Individuals who are pregnant or plan to become pregnant within one month of vaccination
Immune compromised*
Traditional smallpox vaccination is based on an infection with a live replicating (reproducing) vaccinia virus which builds up an immune response in the body 10-14 days after vaccination. The reason why infections with live replicating organisms are dangerous for persons who are immune compromised, is that they cannot generate an adequate immune response and control the infection. Therefore a smallpox vaccine based on a live replicating virus is contra-indicated in this population.
The number of people advised against being vaccinated with traditional vaccines increases beyond 25% because of the risk of inadvertent or accidental infections due to transmission of the virus from the vaccination site. Specifically, persons in close contact with individuals listed above are advised against vaccination with traditional smallpox vaccines because of the potential for accidentally infecting those at risk.
More recently, unexplained cases of heart complications (myopericarditis) were reported in young healthy males in the US military after vaccination with a traditional smallpox vaccine. Even more alarming is that these complications were seen even though all vaccinees were carefully screened and high-risk (immune compromised) individuals were excluded from the vaccination programme.
* Immune-compromised persons are those that have a weakened, under-developed or malfunctioning immune system. This definition includes: HIV infection, cancer, an organ transplant, Primary Immune Deficiency disorders, some severe autoimmune disorders, immunosuppressive medications and other illnesses can weaken the immune system.
