As with all medication or biological products, people can be allergic to certain vaccines.
Immediate allergic reactions or anaphylaxis to vaccines are rare. These reactions usually start within minutes following the vaccination and are characterized by the same symptoms as immediate reactions to other allergens; skin manifestations (urticaria, swelling, itching), respiratory manifestations (cough, difficulty breathing, wheezing) and a reduction in blood pressure (weakness, loss of consciousness). If a significant immediate allergic reaction is suspected, it must be treated rapidly with epinephrine. It is important that the person suffering from the allergic reaction ultimately be referred to an allergist. Most of the time, allergy testing can confirm the allergy to the vaccine, and the resulting information can be very helpful for future vaccination. In general, most patients allergic to one vaccine in particular can receive other vaccinations without problems.
When symptoms might be due to an allergy (for example urticaria, redness, itching) but follow several hours or days after having received the vaccination, it is unlikely to be a true allergy to the vaccine.
Sometimes vaccines can cause important local reactions that begin in the hours following the vaccination or even the next day. The site of vaccination (usually the arm) can become inflamed, red, and painful. The reaction can last several days. Although these reactions can be quite alarming, they are not typically representative of an acute allergic reaction. There is generally no risk of an immediate allergic reaction with the next vaccination. Consultation with an allergist is not necessary. Vaccines containing the booster DT (diphtheria, tetanus) are more often associated with this kind of reaction.
Certain vaccines use egg embryos during the manufacturing process and so are administered with caution to individuals allergic to eggs. The seasonal flu vaccine contains a minimal quantity of egg protein. The majority of egg allergic individuals can receive this vaccine without an allergic reaction. Depending on the severity of the allergic reaction to eggs, the vaccine can be administered in one or several doses with a prolonged observation time. Previously this vaccine was administered by allergists or in a hospital setting, but due to accumulating evidence of only a very low risk when administered to egg-allergic patients, since 2011 these precautions are no longer obligatory. See also the most recent recommendations put forth by a consensus among university allergists in Québec (French version).
The vaccine against yellow fever, required when travelling to certain countries also contains egg protein. The risk of allergic reaction is higher with this vaccine than it is with the flu vaccine. A consultation with an allergist is necessary in order to evaluate the risk and to proceed with vaccination if possible.
The RRO (or MMR) vaccine (against measles/rougeole, mumps/oreillons and rubella/rubéole ) does not contain a significant quantity of egg protein. It has been known for many years now that this vaccine can be given without particular precautions to egg allergic individuals. An allergy consultation is not necessary and the vaccine can be given in the regular setting for recommended vaccinations.
Marie-Noel Primeau, MD
(translation by Andrew Moore, MD FRCPC)
NB : This article is not referring to desensitization or immunotherapy, which is typically prescribed to treat allergies to dust mites, pollens, or wasps, and which is sometimes referred to as "vaccines". This subject is treated in the Respitatory section (Immunotherapy).