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.
The 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.
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.
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.