Yellow fever vaccine
Yellow fever vaccine
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Live, attenuated yellow fever virus
Vaccine Strain Characteristics
- The only approved vaccine for use world-wide is a live, attenuated virus derived from the original lot, 17D yellow fever virus strain, created by passing the wild-type virus repeatedly in cultures attenuate its virulent properties while ensuring it would induce immunity to the virus in vaccine recipient.
- There are two 17D strains in use today (with 99.9% sequence homology)
- 17D-204: found in the US licensed vaccine (YF-VaxTM)
- 17DD: manufactured in Brazil
- The attenuation process used minced chick embryo cultures (no brain or spinal cords included), and the final passage prior to human use was in embyronated eggs.
- The vaccine is comprised of a quasi-species as the vaccines are not plaque-purified and contain heterogeneous sub-populations with differing mouse-brain neurovirulence.
Non-Virus Constituents in the Vaccine
- No antibiotics or preservatives are part of any yellow fever vaccine manufactured worldwide.
- Vaccine is lyophilized for storage and must be reconstituted before use.
- Must be administered within 60 minutes of reconstitution to insure potency and to avoid bacterial contamination.
- Manufacturer variability: salt, buffers, and stabilizer excipients.
- Stabilizers are needed to maintain potency.
- UK and U.S.: sorbitol and porcine gelatin for stabilization.
- France: sugars, amino acids, and divalent cations for stabilization.
Viremia following 17D Yellow Fever Vaccination
- 17D vaccine induces minimal virus titers in circulating blood as opposed to the high virus titers seen in natural yellow fever virus infection.
- Similar onset to natural infection: ~ day 4 following inoculation, ends about time of neutralizing antibody appearance day 8 or 9 (see Immune Response below).
- Vaccine titers are below threshold for uptake by the mosquito virus vector of yellow fever.
- Thought to explain the low risk of maternal-fetal transmission and low rates of neurotropic and viscerotropic vaccine adverse effects.
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