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Third-generation Smallpox Vaccines

Third-generation smallpox vaccines such as IMVAMUNE® are being developed as a safe and effective vaccine without the complications associated with traditional smallpox vaccines. IMVAMUNE® is based on a strain of the Modified Vaccinia Ankara (MVA) virus, which was used during the smallpox eradication campaigns in Germany in the 1970's. More than 120,000 people known to have a high risk of developing complications from the traditional smallpox vaccine were pre-vaccinated with MVA in order to reduce the side-effects of the traditional vaccines. All tolerated the regime, proving MVA to be safe and effective.

Second-generation smallpox vaccines are produced using the Lister-Elstree or New York City Board of Health Vaccinia strains in qualified cell cultures according to good manufacturing practice standards. However these vaccines are documented to cause complications and are not suitable for immune-compromised individuals (people with HIV, undergoing cancer treatment or organ transplantation, with eczema or psoriasis, the very young and old, or who are pregnant).

First-generation smallpox vaccines are those harvested directly from animals. While history has shown them to be effective, they often contain impurities and bacteria that greatly increase the risk of reaction and/or complications. Also, similar to second generation vaccines, they cannot be given to immune-compromised individuals (people with HIV, undergoing cancer treatment or organ transplantation, with eczema or psoriasis, the very young and old, or who are pregnant), or house-hold contacts.

For approximately 25% (1) 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 (2)

Traditional smallpox vaccination is based on an infection with a live replicating (reproducing) vaccinia virus which elicits 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.

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 (3). 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.

(1) Kemper et al, Eff Clin Pract. 2002; 5: 84-90

(2) 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, immuno-suppressive medications and other illnesses that can weaken the immune system.

(3) ACAM2000 Prescribing information 08/2007