Since the human swine flu epidemic started in May, the number of infected has become too high to be counted in Hong Kong. According to the Centre for Health Protection, there are more than 33,100 laboratory-confirmed cases, and the real number is at least 10 times higher. Since most of those aged below 60 have no antibodies against this new virus, and animal studies showed that the virus can multiply much better than seasonal influenza virus in the lungs instead of just multiplying in the nasal cavity, and that the virus can mutate at any time to become tamiflu-resistant or more virulent, it would be wrong to prepare for this epidemic as just a simple seasonal influenza peak in the coming winter.

While the developing nations criticized Hong Kong and the mainland for being excessive in control measures taken for this apparently "mild" disease, they soon realized that it is indeed a necessity to buy vaccine for protecting everyone in their countries. Developing nations cannot afford to buy this new vaccine, as the price is three times that of seasonal influenza vaccine. And while many people in the UK, Europe, China and the US rush to get vaccinated when media in US report that the number of US children succumbing to human swine influenza is three times that of seasonal influenza, people in Hong Kong are worrying about the side effects of the vaccine. These worries are not completely unfounded.

The unusually high incidence of Guillain Barre Syndrome, a disorder resulting in 10 cases of paralysis per million vaccinations, in the 1976 swine influenza vaccination, has been the major cause for concern. The recent incidents of drug contamination in Hong Kong leading to deaths have also decreased the trustworthiness of pharmaceutical products. Moreover, just last week, there was one recall of a batch of new flu vaccine in the US due to diminished potency. Thus, even doctors and nurses openly voiced their reservations about vaccination in mass media, which may have fuelled fears. The image of a paralyzed person, incurable and completely dependent on care from others overwhelms the data indicating that the risk of paralysis is low - less than 1 per million after 40 million doses given in the US.

However, even experts cannot guarantee that the vaccine is 100 percent safe, because there are always allergic reactions that can, in rare cases, be fatal. Parents or guardians, when making the choice for their children or dependent elderly, are more disturbed by the harm caused by vaccination than by the flu itself. In an open society where people cannot accept any death from a treatable cause or from treatment, the slightest doubt about the safety of vaccines will deter the public from using it for prevention. The public tends to play safe and wait, as they want the guarantee of a zero risk.

With the technology of vaccine manufacturing better now than 30 years ago, impurities have decreased by 10 to 100 times. At present, after 40 million doses in the US, the death rate among those vaccinated is 0.28 per million, which is probably not related to vaccination. On the other hand, in Hong Kong, 1.6 healthy persons per million died from human swine influenza. For high-risk groups, 14 persons per million died. Based on experiences in Australia and North America, the projected number of deaths during this winter in healthy people may amount to 14-56, and 72-288 in high risk groups locally. Once patients develop severe symptoms, antivirals do not appear to be very effective.

While vaccination is the most effective way to prevent morbidity and mortality, it has never been risk-free. But the risk is much lower than the figure of 20 per million in traffic accidents every year. Lessons from tetanus, diphtheria, polio and other infectious diseases have clearly shown that it is very difficult to reduce the last few percent of deaths from infectious diseases except through the launch of an extensive vaccination program. Vaccination, especially for high-risk groups, including the young, old and pregnant or those with underlying illness, is therefore recommended for this new pandemic.

During the 1970s, when the media reported the possible association of brain damage with pertussis vaccine, and in 1997, the possible association of autism with measles vaccine, the vaccine uptake rates fell by 30 percent, followed by outbreaks and deaths from pertussis and measles in many infants. Subsequent scientific investigation clearly showed that the risks associated with pertussis vaccine are very low and that there is no relationship between measles vaccination and autism, but many lives were lost unnecessarily.

The author is head of the Department of Microbiology, the University of Hong Kong Li Ka Shing Faculty of Medicine

(HK Edition 12/24/2009 page1)