Store at 2° to 8°C (35° to 46°F). DO NOT FREEZE. Do not use vaccine after expiration date. YF-VAX does not contain a preservative. The following stability information for YF-VAX is provided for those countries or areas of the world where an adequate cold chain is a problem and inadvertent exposure to abnormal temperatures has occurred. Half-life is reduced from approximately 14 days at 35° to 37°C to 3-4.5 days at 45° to 47°C.