About Smallpox Vaccines
There is no cure or treatment for smallpox once infected. The
only protection is vaccination. Traditional smallpox vaccines
(First and second generation vaccines) are effective but considered
unsafe due to high rates of serious adverse events; this includes
death and severe disability. The 2003 US vaccination program for
health care workers, involving more than 37,000 individuals,
confirmed these severe side-effects (1). On top of these severe
side effects, 25% of the general population is contraindicated to
traditional vaccines due to underlying disease conditions, such as
immune suppression and atopic disorders; this includes members of
their households (2). Furthermore, the recent experience from the
pivotal ACAM2000 (second generation vaccine) trials showed that 1
out of 145 healthy subjects subjects developed heart inflammation
(4).
Due to these factors, there is clearly a high need for a new and
safer smallpox vaccine.
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
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
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% (2) 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 (3)
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 (4).
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) Casey et al, JAMA, Dec. 2005, vol. 294, no. 21
(2) Kemper et al, Eff Clin Pract. 2002; 5: 84-90
(3) 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.
(4) ACAM2000 Prescribing information 08/2007
