Yf-Vax Pharmacology, Pharmacokinetics, Studies, Metabolism - Yellow Fever Vaccine

Yf-Vax Pharmacology, Pharmacokinetics, Studies, Metabolism - Yellow Fever Vaccine

CLINICAL PHARMACOLOGY

Yellow fever is an acute viral illness caused by a mosquito borne flavivirus. Infection with the virus may cause a potentially lethal pansystemic disease with fever, jaundice, renal failure and hemorrhage.¹ Yellow fever is endemic in the tropical areas of equatorial sub-Saharan Africa and tropical South America, but has never been seen in Asia.

Disease control includes protection from mosquitoes, elimination of A. aegypti from urban areas, and immunization of those at risk of exposure. Six fatalities from yellow fever were reported between 1996 and July 2002, among unimmunized American and European travellers who visited rural areas within the yellow fever endemic zone. ²

YF-VAX^® [Yellow Fever Vaccine] is a live, attenuated yellow fever vaccine made from the 17D-204 virus strain. A clinical study to evaluate the serological responses and adverse reactions of Aventis Pasteur Inc.’s YF-VAX^® was performed on healthy young adults. One group of six received yellow fever vaccine non-avian leukosis virus-free (non-ALV-free) (manufactured by Aventis Pasteur Inc.) and another group of 18 received an immunization with YF-VAX^®.³ Immunologic protection was measured utilizing a serum neutralizing antibody assay. No neutralizing antibody was detected before immunization. Both groups demonstrated a 100% conversion in the post-immunization sera. The incidence and severity of adverse reactions in each group were comparable.³

In a study involving 101 Nigerian women in various stages of pregnancy, it was concluded that vaccinating pregnant women with the 17D strain of yellow fever vaccine was not associated with adverse effects on the fetus or with risk of fetal infection. However, the percentage of pregnant women without neutralizing antibodies, who seroconverted, was significantly less than a non-pregnant control group (38.6% vs. 81.5%).⁴ On the basis of clinical evaluation of 81 infants in two different studies who were born to mothers vaccinated in pregnancy, infection of the fetus with 17D strains of yellow fever vaccine occurs at a low rate (i.e.,1 of 81) and has not been associated with congenital abnormalities.^4,5,6 In a recent case-controlled study of women inadvertently vaccinated with a 17D yellow fever vaccine early in pregnancy, no statistically significant increase in rates of spontaneous abortion were observed.^6,7 Information from limited clinical trials in Africa and Europe indicated that the risk from vaccination for pregnant women who cannot avoid mosquito exposure in yellow-fever endemic areas is outweighed by the risk for yellow fever infection.⁶

1. Monath TP. Yellow Fever. In: Plotkin SA and Orenstein WA, editors. Vaccines, 3^rd ed. Philadelphia, PA: WB Saunders Company,1999:815-79.

2. Monath TP, et al. Prevention of yellow fever in persons traveling to the tropics. Clin Infect Dis 2002;34:1369-78.

3. Data on file at Aventis Pasteur Inc.

4. Nasidi A, et al. Yellow fever vaccination and pregnancy: a four year prospective study. Transactions of the Royal Society of Tropical Medicine and Hygiene 1993;87:337 9.

5. Tsai TF, et al. Congenital yellow fever virus infection after immunization in pregnancy. J Infect Dis 1993;168:1520-3.

6. Recommendations of the Advisory Committee on Immunization Practices (ACIP). Yellow Fever Vaccine. MMWR 2002;51(RR-17):1-10.

7. Nishioka S, et al. Yellow fever vaccination during pregnancy and spontaneous abortion; a case control study. Trop Med Int Health 1998;3:29-33.