We retrospectively studied 12 HIV-infected patients vaccinated with the 17D yellow fever (YF) strain. At vaccination, the mean CD4 cell count was 561 ± 363 cells/mm3. A neutralizing YF antibody response in serum was obtained in all patients. There were no significant changes in CD4 cell count or viral load compared with baseline. One patient reported transient fever and pharyngitis. YF vaccine appears safe and effective in HIV-infected patients with CD4 cell counts > 200 cells/mm3.
Yellow fever (YF) is a potentially lethal mosquito-borne viral haemorrhagic fever, endemic in Africa and south America that can be prevented by YF vaccine 17D [1–3]. On theoretical grounds, this live attenuated virus vaccine should not be administered to immunocompromised patients because prolonged viraemia may increase the risk of neuroinvasion and encephalitis, and unrestrained virus replication could enhance damage to the liver and other visceral organs [1,4]. Moreover, a study of asymptomatic HIV-infected children with low CD4 cell counts suggested that such patients may not have been immunized effectively . Although there are few data about the efficacy and tolerance of YF vaccine in HIV-infected patients, recent recommendations stated that asymptomatic HIV-infected patients with CD4 cell counts greater than 200 cells/mm3 who require vaccination for travel should be immunized [2,4].
We report a retrospective study of all consecutive HIV-infected patients vaccinated before a trip to sub-Saharan Africa or south America with the 17D yellow fever strain (Stamaril; Pasteur Mérieux Serums et Vaccines, Lyon, France) in our department between July 1995 and July 2002. The efficacy was evaluated by the measure of neutralizing YF antibody response in serum (seroneutralization, Pasteur Cerba; Pasteur Institute, Paris, France). Tolerance data were retrospectively collected from the medical charts and by a specific interview.
Twelve patients (nine women, three men) were studied, including two patients with previous AIDS-related events. At the time of YF vaccination, nine patients were taking antiretroviral treatment. The mean age was 39 years (22–50), mean CD4 cell count was 561 ± 363 cells/mm3 (range 240–1300), mean CD8 cell count was 947 cells/mm3, and mean viral load was 5477 ± 9662 copies/ml (range 20–31 100). For 10 patients, the CD4 cell count and viral load during the 3 months following vaccination were available. There were no significant changes in the CD4 cell count (542 ± 401; P = 0.6) or viral load (8694 ± 11 098; P = 0.2) compared with baseline values. For the five patients with undetectable viral loads (< 200 copies/ml) before vaccination, the viral load was still undetectable after. One patient reported transient fever and pharyngitis 5 days after the vaccination. Serological values indicated a good immune response for all patients with a median YF neutralizing antibody titre of 1/40 (1/20–1/80) (see Table 1).
Although four cases of fever and multisystem organ failure associated with 17D-204 YF vaccination, including three fatal cases, were recently reported , there are no reports of severe adverse events of YF vaccine in HIV-infected patients . Few studies have addressed the efficacy and tolerance of YF vaccine in HIV-infected patients. Two of them concluded that the efficacy and tolerance of YF vaccine were similar in HIV and non HIV-infected patients [7,8]. However, the first study was reported at the international conference of travel medicine in 1995 , before the advent of highly active antiretroviral therapy, and has not been published since; the second study only reported data on two patients . A third study on asymptomatic HIV-infected children  suggested thathat the anti-amarile antibody response was poor in these patients. However, these results were discussed because the serological effectiveness in the control group (75%) was less than that usually reported (95%) [1,2], suggesting that vaccine storage or administration were less than optimal, and the CD4 cell counts were not determined in that study performed in Ivory Coast.
Our study supports recent recommendations of the Advisory Committee on Immunization Practices  in showing favourable results for the tolerance and efficacy of YF vaccine 17D in HIV-infected patients with CD4 cell counts greater than 200 cells/mm3. No significant CD4 cell decrease or viral load increase was observed after vaccination. The rate of reported adverse events (one out of 12) was similar to that usually reported [1,2]. Above all, all patients developed protective antibody response after anti-amarile vaccination. The main limitation of this retrospective study is the absence of the systematic collection of adverse events and viral loads and CD4 cell counts at predetermined times after vaccination.
In conclusion, YF vaccine appears to be safe and effective in HIV-infected patients with CD4 cell counts above 200 cells/mm3, even if they have previously developed AIDS or if their viral load is above 10 000 copies/ml.
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