People with HIV should not receive smallpox vaccination unless they have had contact with smallpox or a smallpox-infected person, according to the smallpox vaccination plan issued by the US Center for Disease Control.
An article in the 15th February edition of Clinical Infectious Diseases provides an outline of the CDC’s recommendations concerning smallpox vaccination in people with HIV, as well as detailed examination of the issues raised for HIV-positive people.
CDC recommendations
According to the CDC, smallpox vaccination should be voluntary. People with HIV are not recommended to receive it, unless they have had contact with smallpox or somebody infected with it, in which case they should be vaccinated.
The CDC point out that people with immunodeficiencies including HIV can develop severe complications after smallpox vaccination, including generalised and progressive vaccinia. HIV-positive people should avoid close contact with people who have received the smallpox vaccine due to the risk of contact vaccinia.
Treatment for vaccinia should consist of immunoglobin (VIG) and/or cidofovir. However, both these treatments are investigational.
Additional points of note
The following additional issues are highlighted in the article.
Mortality – In an unvaccinated population, the mortality rate during a smallpox outbreak would be between 10% and 30%. In people with AIDS or with a CD4 cell count below 200 cells/mm3 “the mortality rate is likely to be very high.”
Immune response to vaccination – Experience with other vaccines indicates that immune response is dependent on CD4 cell count. In people with CD4 cell counts of 200 cells/mm3 or below, antibody responses to vaccines such as hepatitis B and influenza “are nil or greatly reduced.” However, response rates are better in people with higher CD4 cell counts.
Smallpox vaccination and HIV disease progression – Smallpox is a live vaccination and this could cause a persistent increase in CD4 cell activation and HIV viral load.
Risks of smallpox vaccine associated with HIV infection – “Progressive vaccinia…is the risk.” This is seen primarily in people with compromised cell-mediated immunity, including people with AIDS. The reaction involves progressive enlargement of the site of the vaccination with spread of virus around the body causing between ten and 20 additional skin lesions and is usually fatal. A documented case involved a 19 year old soldier with undiagnosed advanced HIV infection who was vaccinated against smallpox in 1984 and died of disseminated vaccinia and AIDS-related illnesses within 18 months. However, it was subsequently established that 300 other HIV-positive soldiers had received smallpox vaccination without incident. Other cases of smallpox vaccination and death examined in the study all involved people with severe immune suppression and late-stage HIV disease.
Treatment for progressive vaccinia – Intramuscular injections of VIG are the standard treatment and laboratory tests suggest that cidofovir may also be a useful treatment. However, “perhaps the most important therapeutic intervention would be HAART combined with other treatments.”
Secondary spread of vaccinia to people with HIV – People with HIV should be removed from direct contact with vaccine recipients, including health care workers involved in HIV care.
HIV screening – Although the CDC plan says that HIV screening should be offered, whether this could happen quickly enough in the event of a smallpox outbreak is highly questionable.
CD4 count – Nearly all complications seen in HIV-positive patients who have received live vaccines occurred when the CD4 cell count was below 200 cells/mm3. It is therefore assumed that smallpox vaccination would be unsafe in people with CD4 cell counts below this level. The situation for those with CD4 cell counts above 200 is less certain “because there has been no experience with this situation.” Indeed, the CDC plan defines risk as the presence of HIV, irrespective of CD4 count. However it is reasoned that CD4 count, disease stage and the success of HAART are “critical variable(s)…in determining risk.”
Earlier smallpox vaccination – People in the US aged over 30 years are likely to have been vaccinated against smallpox as a child. This vaccine is likely to remain effective in people with early HIV-infection and in people with immune reconstitution after HAART.
Further information on this website
Bartlett JG. Smallpox vaccination and patients with human immunodeficiency virus infection and acquired immunodeficiency syndrome. Clinical Infectious Diseases 36 (online edition), 2003.