It was February 1976 when soldier David Lewis fell ill at Fort Dix, New Jersey. He complained of feeling weak and feverish; within days he was dead. An autopsy attributed his death to H1N1, or human swine flu. Thirty-five years later and 13,000 kilometres around the world, Lewis' death and the chain of events it set in motion are still having repercussions in Hong Kong, according to Medical Association vice-president Dr Alvin Chan Yee-shing. They are at the root of fears about the safety of flu vaccines he feels are behind the shunning of the seasonal vaccine in the past two years by a large proportion of Hongkongers. 'Last year only 10 per cent of the population got the vaccination because of phobias,' Chan, chairman of the association's vaccination task force, says. 'That is why an epidemic still occurred and a few middle-aged people with no history of chronic illnesses contracted influenza and died.' Following the soldier's death and fearing a repeat of the 1918 Spanish flu pandemic, which killed up to 50 million people, then US president Gerald Ford ordered a mass immunisation campaign with a hastily produced vaccine. However, within weeks of the campaign getting under way in October 1976, people began falling sick with Guillain-Barre syndrome (GBS), a rare illness in which the body's immune system attacks the nerves, causing numbness, paralysis and sometimes death. As more people fell ill, fears grew of a link between the vaccine and the illness, and the immunisation programme was halted. By that time, December 16, 1976, there had been about 500 reported cases of GBS and 30 deaths. About 40 million Americans had been inoculated - 26 per cent of the population - and a flu epidemic did not occur. Only one person had died: Private Lewis. Chan believes the events of 1976, however they are viewed, sowed the seeds of distrust in the safety of the flu vaccine. Those fears have been compounded over the years by other scares, research projects and anti-vaccine campaigners. One such occasion occurred in 2009, when reports of pregnant women having miscarriages after receiving the human swine flu vaccine discouraged people from getting vaccinated in Hong Kong. As a result, 2.8 million of the government's three million stockpiled vaccine doses were left unused and eventually dumped when they reached their expiry dates, at a cost of HK$220 million. Anti-vaccine groups have also thrived over the past few decades, with the internet proving a useful tool for feeding their doubts and spreading their beliefs. One of the main concerns of the anti-vaccine groups is that many vaccines contain mercury, a heavy metal dangerous to humans that can cause serious illness, including memory loss and respiratory disorders. They have also pointed to research that linked successive yearly seasonal flu shots over five years with a tenfold increase in the risk of developing Alzheimer's disease. Another claim is the vaccine actually weakens the body's immune system, predisposing it to infections, including flu. The Department of Health has repeatedly assured the public that flu vaccines are safe and effective, and drawn attention to the fact that without the vaccine, even healthy people are at risk of a serious case of flu. 'Seasonal influenza vaccination is suitable for personal protection against clinical influenza for all persons except those with known contraindications,' a spokesman said. 'We encourage all persons and, in particular, the high-risk groups to get influenza vaccinations.' The World Health Organisation also maintains that immunisation is safe and effective in preventing flu infection in 70 to 90 per cent of healthy adults. Among the elderly, immunisation prevents severe complications and death in 60 per cent and 80 per cent of cases, respectively, it says. But figures show Hongkongers on the whole are reluctant to have the vaccine. According to the Department of Health, the government vaccination programme gave out 227,000 doses of the 300,000 vaccines it procured last year - down 60,000 from the 287,000 doses given out in the 2009-10 winter. These free shots target those most at risk of serious infection, including elderly people in residential care, those with chronic illnesses, public sector health workers, pregnant women on welfare and people working with poultry and pigs. In addition, its vaccination subsidy schemes helped pay for some 168,000 shots for the elderly and children aged from six months to six years, administered by private doctors last winter, compared to 218,000 in 2009, the year of the swine flu vaccine. This total represents less than 6 per cent of the city's population of 7.1 million - a figure that suggests immunity in the community is too low to protect Hong Kong from an epidemic, Chan says. Research and experience have shown that a virus has difficulty sustaining itself when 20 to 30 per cent of the population is immune, either though previous infection or immunisation. This is what scientists refer to as herd immunity. 'Basically, when there are many people with antibodies, the virus cannot spread so easily and it effectively stops the outbreak,' Chan says. 'But if you have only 10 per cent of the population or less being vaccinated or protected, then 90 per cent of citizens are still vulnerable and an epidemic can still build up momentum.' This is why Chan and the Medical Association's vaccination task force want to see a higher uptake of the seasonal flu vaccine. But first the public's fears about the safety of the vaccine must be overcome, Chan says. 'We need to get people to understand that the advantages far outweigh the risks and that even after incorporating human swine flu into the seasonal influenza vaccine, there has been no increased incidence of side effects.' The vaccine has few side effects and the 2009 cases of miscarriage and sporadic development of GBS were 'most probably' coincidental, he says - and the flu vaccine contains no mercury. Dr Ivan Hung Fan-ngai believes the low uptake of the vaccine has more to do with misplaced complacency than safety fears. 'People think they are healthy and not at risk and that the virus is relatively benign,' Hung, a clinical assistant professor in the department of medicine at University of Hong Kong, says. 'Some think they perform worse after the vaccination, and this is especially true among health care workers. But most people do not realise seasonal flu can be very serious. The reality is that even healthy people aged 40 to 60 with good past health can become very seriously ill with flu. Some of them develop respiratory failure and some die.' According to Hung, GBS only affects one or two people in every million vaccinated. In comparison, out of about 100 severe cases of flu during the winter peak last year, about 40 people died. 'This means six people per 10,000 are at risk of dying with influenza, while the risk of severe pneumonia, myocardial infarction [heart attack] or vascular disease as a result of flu is much higher,' he says. Recent research by Hung and colleagues, published last year in the journal Clinical Infectious Disease, showed the flu vaccine provided a degree of protection against heart attacks and vascular diseases such as stroke. This year's seasonal flu vaccine contains a mix of two influenza A types, human swine flu H1N1 and H3N2, and Brisbane influenza B, which experts believe will offer protection against the viruses circulating this season. The government's vaccination subsidy scheme began in September, while its free immunisation programme will begin next month, ahead of the peak flu season from January to March. Chan hopes the subsidy will be expanded to cover all primary- school children and obese people with a body mass index of more than 30, who are also at high risk. 'In South Korea and Canada, where 30 per cent of the population is vaccinated and they have herd immunity, there have been no epidemics in three years, which has saved a lot of money in terms of medical expenses and sick leave. And, of course, it may have saved lives,' Chan says.