Immunity from old vaccinations may linger.

2003 MAR 12 - (NewsRx.com & NewsRx.net) -- Preliminary research shows people vaccinated against smallpox decades ago could still have a surprising amount of immunity.

Oregon Health & Science University researcher Mark Slifka and his lab assistants have exposed more than 100 blood samples from previously immunized people to a virus closely related to smallpox. That virus, vaccinia, is used to immunize against the disease, which has been eradicated in nature, but which some government officials fear could be revived in a terrorist attack.

When vaccinia is exposed to blood plasma from people who were never immunized, then put into a lab dish with a tissue culture, the virus usually kills all the cells, Slifka said. In recently vaccinated people, however, the virus will kill few to no cells.

By exposing the blood samples to vaccinia and seeing how many cells die, Slifka hopes to gauge how much immunity against smallpox people might have 20, 40 or 60 years after their last vaccination. Slifka said he has seen signs that the body remembers the virus decades after vaccination, and mounts two kinds of immune responses - antibodies that kill the viruses before they infect cells, and T-cells that seek and destroy infected cells.

"Our work is still in its preliminary stages, but people would be surprised by that levels of immunity we're finding," he said.

Slifka supports ongoing efforts to immunize health workers and others ...