Plans to initially vaccinate a half million soldiers and a half million healthcare workers, and eventually at least 10 million Americans against smallpox pose a greater risk to those with compromised immune systems than to healthy people. This disproportionately affects the gay community.
There is both a direct risk to those who receive the vaccination and a small but real risk of secondary transmission. This can occur through close physical contact with a person who recently has been vaccinated.
The smallpox vaccine uses a small infection to generate protection against a larger and more dangerous possible future infection.
The current vaccine uses a live virus known as vaccinia. It is a cousin to the smallpox virus and produces a much milder infection localized at the site of inoculation where the scab forms. It stimulates the immune system to produce antibodies to vaccinia. Those antibodies are cross-reactive—they also recognize and attack smallpox. Thus, generating protection from vaccinia also creates protection from smallpox.
Most vaccines use killed virus, only parts of the virus, or constructs that elicit the same immune response in order to generate immune protection. Smallpox is one of the few vaccines that uses live virus, and that brings with it a series of different issues of safety both for the patient receiving the vaccine and for people who come in contact with that patient.
Federal guidelines recommend against giving smallpox vaccination to individuals with compromised immune systems, whether from HIV, cancer chemotherapy, drugs that suppress rejection of transplanted organs, or for other reasons.
The list also includes people who have experienced eczema or atopic dermatitis, even as a child; and skin conditions such a burns, chickenpox, shingles, impetigo, herpes, severe acne or psoriasis until they are completely healed.
These individual are more likely to experience dangerous side effects from the vaccination. With a severely compromised immune system, it is possible that the vaccinia virus may multiply out of control at various parts of the body and not simply at the site of the inoculation. That appears to have been the case with a soldier vaccinated in 1984 who had undiagnosed HIV.
The site of vaccination is covered with a bandage until the scab that forms has dropped off. This is done to reduce the possibility of secondary transmission. Vaccinia virus can be transmitted through direct contact, on the hands of a person who scratches the site, or through secretions from the site that get into clothing or bedding.
It is theoretically possible for the vaccinia virus to survive a day or two on fabric and still infect someone, Dr. Donald A. Henderson told The New York Times. He is the epidemiologist who led the global effort to eradicate smallpox and is now an adviser to Health and Human Services Secretary Tommy Thompson.
EXPRESSING CONCERN
The National Association of People With AIDS ( NAPWA ) wrote a six-page letter to Thompson Dec. 12, raising 10 concerns 'that must be considered and addressed as part of any smallpox vaccination policy.'
'A blanket refusal to vaccinate all HIV-positive individuals would be misguided,' said Terje Anderson, NAPWA's executive director. Limited data suggests that a person with a relatively intact immune system may be vaccinated safely. He does not want the government to foreclose that option to people who may choose it.
The CDC estimates that at least 200,000 people are infected with HIV and don't know it. Those with advanced disease and a greatly compromised immune system may suffer deadly consequences, as the 1984 example demonstrated. NAPWA is urging education and appropriate screening.
Even less is known about the risks to those who recently contracted HIV and are in the stage of acute infection—generally the first 90 days before the immune system develops antibodies to the virus. Standard screening for HIV measures antibodies and cannot identify recent infections, only the PCR assay that measures viral load would identify such recent infections.
And there is no data on whether people with a weakened immune system face an increased risk of acquiring disease through secondary exposure from the vaccinations of others. Anderson asked Thompson to articulate 'the government's view of the degree of risk this possible exposure presents' and the steps it is taking to protect patients from the vaccination of healthcare workers.
'I certainly would not recommend [ vaccination ] for anyone at this point,' said Dr. Douglas Ward. He and two other physicians have a practice in Washington, D.C., with a large number of patients with HIV. Ward emphasized, 'Someone living with someone who is positive should not get the vaccine!'
'If you touch the [ vaccinia ] wound and then yourself or another person, you can create another wound,' said Dr. Ken Haller, president of the Gay and Lesbian Medical Association and a pediatrician in St. Louis. 'It's a live virus and can spread for about three weeks.'
Haller also suggested that the partners of people who are significantly immunocompromised should not get vaccinated.
A safer smallpox vaccine is in the works. It uses a killed virus, a vaccinia that is modified so that the virus is not replication competent, said Dr. Ron D'Amico, an infectious disease specialist at Beth Israel Hospital in New York. It should be safe for people with compromised immune systems and it will not have the risk of secondary transmission.
D'Amico hopes to begin safety trials of the vaccine in February through the ACTG, though the details have not yet been finalized.
