Prevenile West Nile Vaccine Recall

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On April 28, 2010, Intervet Schering-Plough initiated a voluntary recall of the West Nile vaccine Prevenile. A list of the serial numbers for involved batches are at

The company recalled the vaccine after receiving reports of anaphylactic/anaphylactoid reactions. If you purchased Prevenile prior to the recall and have not yet used it, return it to the veterinarian or distributor where you bought it for a refund. This also allows the vaccine to be returned to the manufacturer for study. (Note: If your horse was vaccinated with Prevenile uneventfully before the recall was announced, relax. Anaphylactic reactions occur immediately.)

Reactions.Anaphylaxis is an acute and severe allergic reaction that occurs immediately after coming into contact with the triggering substance. Since it’s an allergic reaction, it will only occur if the person or animal has been previously exposed to the substance, causing the production of IgE antibodies. When exposed to the substance a second time, it binds to the antibody and causes the release of chemicals that cause the reaction. For a vaccine to cause anaphylaxis, the horse must have been previously vaccinated with the same vaccine.

Anaphylactoid reactions are identical in their symptoms but do not require prior exposure to the substance because no antibody is involved. Many drugs have been found to trigger anaphylactoid reactions, and possibly some complex proteins. Anaphylactoid reactions can occur on the first exposure to a vaccine. Although the mechanisms that activate the reaction are different, the signs and symptoms are identical.

The symptoms of an anaphylactic reaction are related to constriction of the airways and dilation of blood vessels. They include weakness, disorientation, trembling, difficulty breathing and abdominal pain. Sweating, diarrhea, hives or generalized edema may also occur. Heart irregularities can occur and the reaction may be fatal. The antidote is epinephrine injection.

No details on the number or location of reactions has been released, but the company appears to have acted fast in recalling the vaccine.

This type of reaction is rarely related to the disease organisms in a vaccine. Reactions to adjuvants, preservatives, proteins from cell cultures used to grow organisms, or alterations caused by improper storage are possible causes.

Bottom Line.Owner and veterinary satisfaction with Prevenile has been high since it was first introduced in 2006. Vets have reported extremely low incidence of vaccine reactions with Prevenile. Many are disappointed to not have access to it this year but are glad the company acted quickly.