For some reason that I have never quite fathomed, immunization against infectious diseases has from its very inception in Jenner’s time been one of the most viscerally feared and bitterly opposed of all medical techniques. Perhaps people felt that to immunize was to interfere sacrilegiously with the course of nature, and that people, especially children, had the duty to die of infectious diseases just as Nature “intended.” Perhaps they felt that, if it worked, it would allow the survival of the unfittest. At any rate, few medical procedures have been as persistently, minutely, and fervently examined for harmful effects as immunization has.

In general, the results have been disappointing for those who wished to show that immunization was invariably followed by Nature’s retribution, particularly in the neurological sphere. Scare has succeeded scare without ever being confirmed, though those who hold to the anti-immunization faith refuse to abandon it. Now, at last, there seems to be evidence of a genuine association between a certain type of immunization and a neurological condition.

That association is that between the immunization of children with an anti-influenza virus and narcolepsy, a condition characterized by chronic, excessive daytime sleepiness and a tendency to cataplexy, that is to say a loss of muscular tone triggered by strong emotion. It was first observed in Finland and Sweden; subsequent studies in other European countries and in Canada failed to find an association, but a further study, this time in England, and reported in the British Medical Journal, confirmed that the Finnish and Swedish findings.

In October 2009, children at risk of pulmonary complications during a pandemic of influenza were immunized against it with a vaccine against the causative virus. Most of the children immunized suffered from asthma (interestingly, one of the theories to account for the recent rise in the proportion of children suffering from asthma and other allergic conditions is that, having been immunized against all the common childhood infectious diseases, their immune systems have not developed as Nature “intended”).