“Vaccinia” Smallpox Vaccine virus

-vs-

“Variola” Smallpox  Disease  virus

 

Center for Biologic Counterterrorism and Emerging Diseases

Medstar Health Group

Washington, DC

 

Director: Daniel R. Lucey, MD, MPH

 

 

A.       Definitions:

o         Vaccinia virus is the DNA orthopoxvirus in the smallpox vaccine. Mortality due to vaccinia vaccine in the USA has been < 0.001%.

o         Vaccinia virus was originally (Jenner 1796)  related to cowpox (Latin “vacca”, cow), but is now clearly distinct  from cowpox.

o         Vaccinia virus does not cause smallpox. 

 

Ø       Variola virus is the DNA orthopoxvirus that causes  smallpox the disease.

Ø       The agent of bioterrorism is Variola major virus, which has a mortality rate > 30%.

 

B.       Transmission:

o         Vaccinia virus from the vaccine is spread  by direct contact and NOT through the air (unlike variola).

o         Vaccinia exists in a live, but weakened, form in the smallpox vaccine.

o         Vaccinia can be transmitted by skin-to-skin contact with the active vaccinia skin lesion that is present in a recently vaccinated person.  Those who become infected in this way can develop adverse reactions to the live vaccinia virus just as though they themselves had been deliberately vaccinated.

 

Ø       Variola virus from a person with smallpox the disease is spread both through the air (+ airborne transmission) and by direct skin-to-skin contact, or contact with variola virus on inanimate objects (“fomites”) such as clothing.

 

C.       Immune Responses

o         Vaccinia  virus vaccine  induces a cross-protective immune response against the variolavirus and thus protects against smallpox disease.

o         If immunocompromised  persons are vaccinated or exposed by contact to vaccinia virus, they can develop life-threatening reactions to the vaccine.

o         These reactions include “progressive (necrotic) vaccinia,” which can be fatal.

 

Ø       Variola virus induces an immune response that is often inadequate to prevent disease and death (mortality is >30%  in persons never vaccinated).

Ø       Immunocompromised persons may have more severe smallpox, with atypical smallpox skin lesions termed “flat-malignant”, or “hemorrhagic” ( > 90% mortality).

 

D.       Therapy:

o         Vaccinia virus: there is no FDA-licensed drug for treating severe vaccinia vaccine reactions.

o         Cidofovir is an antiviral drug that may be studied against vaccinia virus. Cidofovir’s kidney toxicity is decreased by giving it with probenecid.

o         Vaccinia Immune globulin (VIG) is effective for most of the severe vaccinia vaccine reactions.

 

Ø       Variola virus: there is no FDA-licensed drug for treating smallpox disease.

Ø       Cidofovir is an antiviral drug that may be studied on an investigational basis against variolavirus.

Ø       VIG is not effective against variola virus.