Anaphylaxis may occur following the use of YF-VAX vaccine, even in individuals with no prior history of hypersensitivity to the vaccine components.

Yellow fever vaccines must be considered as a possible, but rare, cause of vaccine-associated viscerotropic disease² (previously described as multiple organ system failure), ^2,26 that is similar to fulminant yellow fever caused by wild-type yellow fever virus. Available evidence suggests that the occurrence of this syndrome may depend upon the presence of undefined host factors, rather than intrinsic virulence of the yellow fever strain 17D vaccine viruses isolated from subjects with vaccine-associated viscerotropic disease.^26-29 (See ADVERSE REACTIONS section. )

Vaccine-associated neurotropic disease ² (previously described as post-vaccinal encephalitis¹) is a known rare adverse event associated with yellow fever vaccination. Age less than 9 months and immunosuppression are known risk factors for this adverse event. (See CONTRAINDICATIONS and ADVERSE REACTIONS sections. )

Prior to an injection of any vaccine, all known precautions should be taken to prevent adverse events. The patient's previous immunization history, current health status, and medical history should be reviewed for previous hypersensitivity reactions and other adverse events related to this vaccine or similar vaccines and for possible sensitivity to dry natural latex rubber. The stopper of the vial contains dry natural latex rubber that may cause allergic reactions. In some instances where symptoms appear soon after a vaccine is administered, differentiation between allergic reaction to the vaccine and reaction to an environmental allergen may not be possible.²³

A separate, sterile syringe and needle or a sterile disposable unit should be used for each patient to prevent transmission of blood borne infectious agents. Needles should not be recapped and should be disposed of according to biohazard waste guidelines.

YF-VAX vaccine should not be administered to an individual with a history of hypersensitivity to egg or chicken protein (see CONTRAINDICATIONS section). However, if a subject is suspect as being an egg-sensitive individual, the following test can be performed before the vaccine is administered:²³

1. Scratch, prick, or puncture test: Place a drop of a 1:10 dilution of the vaccine in physiologic saline on a superficial scratch, prick, or puncture on the volar surface of the forearm. Positive (histamine) and negative (physiologic saline) controls should also be used. The test is read after 15 to 20 minutes. A positive test is a wheal 3 mm larger than that of the saline control, usually with surrounding erythema. The histamine control must be positive for valid interpretation. If the result of this test is negative, an intradermal (ID) test should be performed.
2. Intradermal test: Inject a dose of 0. 02 mL of a 1:100 dilution of the vaccine in physiologic saline. Positive and negative control skin tests should be performed concurrently. A wheal 5 mm or larger than the negative control with surrounding erythema is considered a positive reaction.

If vaccination is considered essential, despite a positive skin test, then desensitization can be considered (see DOSAGE AND ADMINISTRATION section, DESENSITIZATION subsection).

CARCINOGENESIS, MUTAGENESIS, IMPAIRMENT OF FERTILITY

YF-VAX vaccine has not been evaluated for its carcinogenic or mutagenic potential or its effect on fertility.

Animal reproduction studies have not been conducted with YF-VAX vaccine. It is also not known whether YF-VAX vaccine can cause fetal harm when administered to a pregnant woman or can affect reproductive capacity. Because of the lack of large-scale controlled studies to verify its safety in pregnancy, YF-VAX vaccine should be given to a pregnant woman only if clearly needed. The seroconversion rate to 17D vaccines is markedly reduced in pregnant women. (See CLINICAL PHARMACOLOGY section. )¹⁸ For discussion of this subject and for documentation of a protective immune response to vaccine where it is deemed essential, the CDC may be contacted at (970) 221-6400.

It is not known whether this vaccine is excreted in human milk. There have been no reports of adverse events or transmission of 17D vaccine virus from nursing mother to infant. However, vaccination of nursing mothers should be avoided when possible, because of the theoretical risk of the transmission of 17D virus to the breast-fed infant. When travel of nursing mothers to high-risk yellow fever endemic areas cannot be avoided or postponed, such individuals may be immunized.

Vaccination of subjects greater than 65 years of age should be limited to individuals who are traveling to or reside in known yellow fever endemic or epidemic areas, because of the increased risk for systemic adverse events in this age group. When vaccination is deemed necessary, the health status of such individuals should be evaluated prior to vaccination. Additionally, if vaccinated, elderly subjects should be carefully monitored for adverse events for 10 days post-vaccination (see ADVERSE REACTIONS section).^24,38

REFERENCES

1. Monath TP. Yellow Fever. Plotkin SA, Orenstein WA (eds. ). Vaccines. 3^rd Edition, WB Saunders Company. 1999;815-879.

2. Recommendations of the Advisory Committee on Immunization Practices (ACIP). Yellow Fever Vaccine. 2002. MMWR 2002;51(RR17):1-10.

18. 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;87:337-339.

23. American Academy of Pediatrics. In: Pickering LK, ed. 2000 Red Book: Report of the Committee on Infectious Diseases. 25^th ed. Elk Grove Village, IL: American Academy of Pediatrics 2000;35-38, 174-175.

24. Aventis Pasteur Inc. Data on File — 080601;120104.

26. Martin M, et al. Fever and multisystem organ failure associated with 17D-204 yellow fever vaccination:a report of four cases. Lancet 2001;358:98-104.

27. Galler R, et al. Phenotypic and molecular analyses of yellow fever 17DD vaccine viruses associated with serious adverse events in Brazil. Virology 2001;290:309-319.

28. Chan RC, et al. Hepatitis and death following vaccination with yellow fever 17D-204 vaccine. Lancet 2001;358:121-122.

29. Vasconcelos PFC, et al. Serious adverse events associated with yellow fever 17DD vaccine in Brazil:a report of two cases. Lancet 2001;358:91-97.

38. Martin M, et al. Advanced age a risk factor for illness temporally associated with yellow fever vaccination. Emerg Infect Dis 2001;7:945-951.

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