The H1N1 strain of the influenza A virus has been a common cause of influenza in the recent years. Vaccination against H1N1 can help to protect against the infection. Some vaccines, however, contain egg protein. So, can an egg protein-containing vaccine be administered safely in patients with egg allergy?
A study was conducted in Norway to answer the above question. Around 80 children ranging from 10 months to 16 years in age were included in the vaccination program which lasted for almost a month. All the children were confirmed to have egg allergy based on either a skin test or if they tested positive for IgE antibodies specific for egg allergy. They were unable to consume any eggs or egg-containing products without suffering from an allergic reaction. A number of subjects included in the study also suffered from other allergies like asthma, eczema and food allergies.
AdvertisementThe vaccine used had an ovalbumin content of less than 0.33 μg/ml (microgram per milliliter). The dose of the vaccine depended on the age of the patient. All the children were divided into three groups. Fractionated doses were administered to one group, that is, one-tenth of the total dose was administered initially, followed by the rest after 30 minutes. Patients in this group had in the past suffered severe reactions to egg protein viz. anaphylactic reactions, cardiovascular-related problems and collapse. In the second group, the vaccine was administered as a single dose. These patients had previously suffered only a mild reaction to egg protein limited to the skin or digestive tract. Nineteen patients, who had an allergy detected on testing but were never exposed to egg prior to the study, were given a divided or fractionated dose.
Thirty-eight patients received the vaccine as a fractionated dose whereas 42 patients received it as a single dose. Patients were observed for 30 to 60 minutes following the vaccination for any allergy.
Only 4 patients who received the egg-protein containing vaccination suffered symptoms following the vaccination. The first patient, a 2 year 8 month old child had a mild skin allergy and loose stools. The second, an 11-month old baby suffered from a skin reaction, but was already suffering from eczema prior to the vaccination. It was thus difficult to attribute the reaction to the vaccine. Sneezing was noticed in an 8 year 7 month old child following the vaccine; however it stopped on its own. These 3 patients were exposed to egg for the first time with the vaccination. They were also administered the fractionated dose of the vaccine. The fourth patient, a 16 year old, showed anxiety features related to taking an egg-containing vaccine and had abdominal pain following the first dose, which was found to be not an allergic reaction. Multiple fractionated doses were administered, following which allergic reaction was not observed. Thus, only one patient showed a mild clear allergic reaction, whereas 2 suffered from possible allergic reactions.
The study thus confirmed that patients with a known allergy to egg can be administered the H1N1 vaccine containing less than 0.33 μg/ml ovalbumin, the egg protein, even if they had suffered from a severe reaction to egg in the past. Although a fractionated dose was used in some cases, it may not be necessary in patients receiving vaccines containing the low concentration of egg protein.
The study also deduces that the level of antibodies specific for egg protein may not be useful to predict the severity of reaction and should not be considered while deciding if a vaccine should be administered as a fractionated dose or not.
Reactions of Norwegian children with severe egg allergy to an egg-containing influenza A (H1N1) vaccine: a retrospective audit; Dr. Bard et al; BMJ Open 2012.