This year, adverse reactions occurred frequently in young children receiving the seasonal flu vaccine, which now contains a swine flu component.

In Western Australia, of about 25,000 children vaccinated, more than 250 had adverse reactions including 55 with febrile convulsions. Thus for every 500 children vaccinated, about one child developed a febrile seizure —  a very high rate.

Previous CSL flu vaccine studies showed that children frequently developed fevers shortly after vaccination, and very young children developed fevers at twice the rate of older children. The effect was dose-dependent; the larger the vaccine dose, the more side effects. In children under 3 years, 62% developed a fever after a 30-microgram dose and 23% after a 7.5-microgram dose ( See here and here).

Fevers in young children following flu vaccination appears to be very common. Data is, however, generally either difficult to find or underplayed. In Glaxo studies, 43% of very young children had fevers of  >38C after their second vaccine dose. In an earlier CSL seasonal flu study, 40% had a fever after a booster vaccination and one child of the 298 recipients developing a febrile convulsion.  Another needed overnight hospital admission for associated fever and vomiting. US studies from the 1970s, also showed fevers soon after vaccination were frequent in young children.

Fever is THE risk factor for febrile convulsions. Surprising when the CSL sponsored swine flu vaccine study was published early this year, the much higher rate of fever in very young children was not given much prominence and its extent only evident in the more difficult to find supplementary tables. Nor is this issue highlighted in the vaccine’s product information.

Internationally there is relatively little data available on either the benefits or side-effects when young children are vaccinated against influenza. Some pharmaceutical companies have even withheld safety data from clinical studies. In a recent review it was noted that “In children under the age of two, the efficacy of inactivated vaccine was similar to placebo. It was not possible to analyse the safety of vaccines from the studies due to the lack of standardisation in the information given but very little information was found on the safety of inactivated vaccines, the most commonly used vaccine, in young children.”

It is surprising that more explicit warnings about the high risk of adverse reactions are not given to parents when their children receive flu vaccines. There is also no prospective, post-marketing surveillance in place to look for serious reactions that might occur in large numbers of children (many thousands), given data from many studies show the frequent association of high fevers. Passive surveillance is in place in Australia, but this has relatively poor performance in finding adverse reactions.

Last winter, the likelihood that a child without risk factors would die from swine flu here was less than one in a million. When such a high proportion of children develop moderate to severe febrile reactions to the influenza vaccine, it’s likely that we’ll cause more harm than good by vaccinating the entire population.

Vaccination against many infections continues to be of our most successful public health interventions.

Influenza vaccines, however, need to be given yearly, are of much lower efficacy than many other vaccines and seem comparatively to be associated with higher side effect profiles, especially in young children.

We therefore need much better and larger studies on safety and efficacy before we roll out whole of population influenza vaccine programs, especially to those without risk factors and to children — who appear to have much higher rates of adverse reactions.