As I never tire of telling my marketing students, brands and corporate reputations ultimately exist only in the mind of the customer. Never was the power of the mind more vividly illustrated than last week, when accounts of adverse reactions to the new Gardasil cervical cancer vaccine wiped more than $1 billion off the value of CSL Limited, as reported by Jane Nethercote in Friday’s Crikey.

CSL’s share price fell in response to media reports about 20 girls at Sacred Heart Girls College in Melbourne being affected by Gardasil vaccination. In fact, accounts of the girls having headaches, nausea, dizziness, fainting and relapsing illnesses after receiving Gardasil, a vaccine against the human papillomavirus which causes cervical cancer and genital warts, have all the classic hallmarks of “mass sociogenic illness”.

MSI is a well-documented phenomenon that has caused trouble for another high-flying Australian company in recent years. It was almost certainly responsible for the “mystery gas leak” in the Virgin Blue terminal at Melbourne Airport in February 2005, which closed the terminal for several hours, disrupted flight schedules for two days, cost Virgin Blue an estimated $3 million and damaged the airline’s reputation when its crisis management and public affairs responses went into meltdown.

No gas was ever actually detected and the report of the subsequent inquiry by Victorian Emergency Services Commissioner Bruce Esplin failed to identify any toxic substance or cause for the symptoms of the 57 people treated, 47 of whom were taken to hospital.

There are some 200 published accounts of MSI from around the world, many of them based in schools, and vaccination has been the trigger for “outbreaks” that are among the largest ever recorded. In Jordan in 1998, more than 800 students reported symptoms following a standard diphtheria-tetanus injection, after well-meaning media comments from educational and public health personnel led to a kind of officially sanctioned panic; 122 were admitted to hospital. Extremely thorough epidemiological follow-up proved that there was no contamination of the vaccine or other tangible cause, and all of the students recovered quickly and without complication.

One of the classic signs of MSI is contagion by “line of sight”, sound or oral communications; that is, the only people who fall ill are those who see someone else fall ill or hear about it. In a real gas leak or vaccine contamination, you would expect symptoms in people who were distant from, and unaware of, other cases.

Clinical experience suggests that if you vaccinate schoolchildren, and especially teenage girls, one at a time so that they can’t see each other before or after the needle, then the rate of adverse reactions drops almost to zero.

Of course, MSI is merely a less pejorative term for what in previous eras went by names like “mass hysteria”. It’s often considered in medical and public health circles to be a “diagnosis of exclusion”, meaning that it is invoked only when all other potential “real” causes have been investigated and eliminated. Unfortunately, properly eliminating other causes of “gas leaks” or reactions to a vaccine can take weeks or months of toxicological testing and epidemiological detective work, leaving an information void that some in the media can’t help but try to fill.

The Esplin report on the Virgin Blue affair found that a variety of people and agencies with apparent authority, including reporters, had used “loose terminology” including words and phrases like “toxic”, “noxious” and “dropping like flies”, and that this had contributed to false perceptions of the seriousness of the situation. More comprehensive reviews of the epidemiological evidence like this one have also found that media coverage plays a significant role in enhancing the spread of outbreaks of MSI.

Yet, now we’re seeing it all over again in the case of Gardasil. Despite appropriately cautious but reassuring statements from CSL and medical authorities including the vaccine’s inventor, Professor Ian Frazer, 3AW’s Neil Mitchell has appointed himself epidemiologist to the masses. Last Thursday he weighed in on air and in print, throwing around words like “scare”, “alarm bells”, “nasty side effects”, “collapse”, “numbness” and “temporary paralysis”. According to Mitchell, reasonable reassurances from knowledgeable authorities based on actual data were “condescension” and “dismissive statements”.

So now, who’s being hysterical? And by the way, the timing’s great, Neil … just as the first cohort of girls vaccinated with Gardasil fall due for their second injection. Guess what they’re all talking about as they wait in line this time: “Did you hear about the girls at Sacred Heart …?”