Since the immunity issue was mentioned re smallpox, I thought I'd post this from my inbox:
Thank you for your inquiry to CDC-INFO. In response to your request
for information on vaccines, including immunity to smallpox, please refer
to the following information.
Someone who was vaccinated against smallpox decades ago may retain some
immunity but it is not known for certain that this level of immunity
would protect them from smallpox today if exposed. Information on a
naturally occurring immunity to smallpox not occurring through an active
infection was not identified in CDC resources.
Cell-mediated immunity most likely plays the primary role in the
recovery from smallpox infection. Antibodies play a secondary role in
recovery, though they play a primary role in protecting against re-infection.
The presence of viral neutralizing antibodies is considered a
reasonable marker of immunity.
Epidemiologic studies demonstrated that a high level of protection
(nearly 100 percent) against smallpox persists for up to 5 years after
vaccination and substantial but waning immunity for ten years or more.
Vaccines interact with the immune system and often produce an immune
response to a specific disease similar to that produced by the natural
infection, but they do not subject the recipient to the disease and its
potential complications. Vaccines produce immunologic memory similar to
that acquired by having the natural disease.
Many factors may influence the immune response to vaccination. These
include the presence of maternal antibody, nature and dose of antigen,
how the vaccine is given, and the presence of adjuvants (materials added
to improve how well the vaccine works).
Host factors such as age, nutritional factors, genetics, and coexisting
disease, may also affect the response.
More information about vaccines and how they work is available in the
Understanding Vaccines (PDF)
Understanding the Immune System (PDF)
Immune System, NIAID, NIH
(http://www3.niaid.nih.gov/topics/immuneSystem/default.htm - broken link)
If your friends are concerned that they are not protected against
vaccine-preventable diseases, please encourage them to speak with their
For more information about vaccines and about smallpox, please visit
the CDC website:
Vaccines and Immunizations
Vaccines: HOME page for Vaccines and Immunizations site
Frequently Asked Questions About Smallpox
CDC Smallpox | FAQ About Smallpox
Smallpox Basics: Information for the General Public
CDC Smallpox | Smallpox Disease
Additional information can be found at:
http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/smallpox.rtf (broken link)
Thank you for contacting CDC-INFO Contact Center. Please do not
hesitate to call 1-800-CDC-INFO, e-mail firstname.lastname@example.org
if you have any additional questions.
CDC-INFO is a service of the Centers for Disease Control and Prevention
(CDC) and the Agency for Toxic Substances and Disease Registry
(ATSDR). This service is provided by Vangent, Inc. under contract to CDC and