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11/4/2002

FDA Relicenses Old Smallpox Vaccine

Kate Traynor

The Food and Drug Administration (FDA) recently approved the licensing of Wyeth Laboratories' vintage smallpox vaccine, Dryvax, the current stocks of which date from 1983 or earlier.

Dryvax consists of purified, lyophilized lymph material obtained from the skin of bovine calves infected with the New York City Board of Health strain of vaccinia virus. The newly licensed product is configured as 100-dose kits, each containing one vial of lyophilized vaccine, a diluent-filled syringe, and a box of bifurcated needles for administering the reconstituted vaccine. The product's FDA-approved labeling was not immediately available.

Routine vaccination against variola, the virus that causes smallpox, was halted in the United States in the 1970s, and the disease was declared to be eradicated in the wild in 1980. Wyeth subsequently stopped making Dryvax for routine administration but maintained stocks of the vaccine in storage. The possibility that smallpox could be used as a bioterrorism agent has renewed national interest in vaccinating at least a portion of the U.S. population against the virus.

Two recently completed clinical trials have indicated that the current U.S. supply of Dryvax remains potent, and that the vaccine can be prepared at a 1:5 dilution or weaker and still generate a good immune response in adults.

A National Institutes of Health-funded study of the vaccine's safety and effectiveness in young children was recently proposed but is on hold pending the receipt of public comments. According to a notice in the Oct. 31 Federal Register (PDF), Dryvax is considered an investigational new drug for this study, because the protocol calls for diluting the vaccine 1:5 for one group of children. The notice states that "there are no data to support the efficacy of the 1:5 dilution of this product in children."

The Centers for Disease Control and Prevention (CDC), in an attempt to replace Dryvax with a vaccine produced under modern conditions, awarded contracts to United Kingdom-based Acambis PLC in 2000 and 2001 to produce tissue-culture derived smallpox vaccines.

Acambis announced in September that the company has shipped the first finished doses of vaccine for inclusion in the National Pharmaceutical Stockpile and expects to deliver the remainder of the material in the next few months. According to the company, every person who participated in the Phase I clinical trials of the vaccines mounted an appropriate immune response, and none suffered serious adverse events. Acambis continues to test its smallpox vaccines and predicts that FDA will approve the products by early 2005.