FOR several years, scientists knew a flu pandemic was looming and had hedged all their bets on the next big one being the H5N1 or bird flu strain.

But they were suddenly blindsided by a new strain of the flu virus  - the H1N1 - which has since been reported in more than 200 nations and has killed more than 10,500 people worldwide.

Speaking at the Emerging Infectious Diseases Conference here recently, Professor Malik Peiris from the University of Hong Kong said H1N1 had not been on the list of possible pandemic flu strains.

"We got that prediction wrong. We assumed that as type HI flu was already in the population, there would be enough immunity in the community," said the virologist and infectious disease expert. "But all that attention on H5N1 led to logistics important in this H1N1 pandemic."

For example, research on the H5N1 virus found that it did not produce a good immune response when used in ordinary flu vaccines. That led to the development of new adjuvants - a chemical additive which boosts vaccines' potency.

Prof Peiris explained that although the H1N1 strain does not need an adjuvant in the vaccine, the adjuvant has helped in making a little virus material go a longer way in terms of vaccine potency.
 
The World Health Organisation (WHO) carries out continuous surveillance to identify circulating influenza viruses. It then recommends which strains should be included in the seasonal shots.

WHO has two strain-selection meetings every year one in September for the Southern Hemisphere influenza season to plan for the coming year from May to October and another in February for the Northern Hemisphere flu season from November to April.

It was due to the ongoing surveillance programme that the H1N1 virus was identified in the United States and Mexico at the end of April.

The five to six months taken to make the H1N1 pandemic vaccines available is standard for seasonal flu vaccines which typically do not cause much public concern as they are long tried and tested.

Both seasonal and pandemic flu vaccines are made in the same way.

What changes is the type of flu strain used and this depends on advice from WHO on the combination of strains needed in vaccines for that particular season.

The use of the same production methods means that the safety of even new flu vaccines is assured and these do not have to go through years of testing like new drugs do. Prof Peiris said: "The H1N1 vaccines are made exactly the same way as the seasonal flu vaccine ... the only difference is the virus I don't believe this particular vaccine is inherently more risky than the seasonal flu vaccine."

There were some concerns that the H1N1 vaccines had been rushed out due to the pandemic nature of the flu.

Several deaths have been reported among those who had taken the doses in Germany and China. So far, WHO investigations have ruled out a "direct link to pandemic vaccine as the cause of death".

The WHO pointed out that, in China for example, where more than 11 million doses of H1N1 vaccine have been administered, the health authorities report only two deaths. "Thorough investigation of these deaths, including a review of autopsy results determined that underlying medical conditions were the cause of death, and not the  vaccine," the WHO website said.

The WHO estimates about 65 million people worldwide have been vaccinated.

There are about six pharmaceutical companies producing H1N1 vaccines and Singapore's stock comes from two.

Out of a total of 1 million doses of H1N1 vaccines imported, 700,000 are Panvax vaccines from Australian firm CSI, and 300,000 are Pandemrix vaccines from UK based GlaxoSmithKline (GSK). Another 300,000 doses from CSL have been ordered.

So far, there have been only a handful of people here who developed side effects after taking the vaccine, although theseare considered non-serious side effects commonly expected from all flu vaccines.

Only about 405,000 doses have been ordered here so far Singapore's Ministry of Health (MOH) did not speculate on the reasons for the seemingly low take-up rate.

But 60 clinics The Straits Times contacted all said many patients were concerned about the vaccines side effects.

Dr Henry Yeo from Bedok Medical Centre said: "Some ask if the vaccine is safe since it s relatively new and some have read online that it may cause side effects.

"Those who come for the vaccine are given a government advisory before the injection. There have been one or two who have walked out after reading the handout, but it s rare."

Dr Chua Tee Lian of C K Family Clinic in Upper East Coast Road said most of his patients' fears have abated but they were still concerned over the deaths overseas. "This risk is very low.  Those who died had other underlying conditions which resulted in complications not directly linked to taking the vaccine."

Both CSL and GSK have long and established track records making flu vaccines.

GSK was formed in 2000 but has its origins in the 1700s. It is  researching both medicines and vaccines for the WHO'sthree priority diseases - HIV/AIDS, tuberculosis and malaria and distributes 35 vaccines every second.

CSL has been at it for more than 40 years and its current H1N1 vaccine is identical to the seasonal flu vaccine apart from the flu strain used.

The GSK version, though contains an adjuvant, which means a smaller dose is needed within the vaccine GSK came up with its own adjuvant containing vitamin E, squalene - which occurs naturally in humans - and polysorbate, which is used in ice cream to keep its texture.

GSK's pandemic centre of excellence medical director Richard South said: "We've been developing this vaccine for many years so we can assume the vaccine with H1N1 in it is equally safe."

GSK's clinical trials of the H1N1 vaccine are ongoing, but Dr South explained that this is usual to monitor safety and immunity. It was not that the vaccine is unsafe he explained but the tracking was being done to gather comprehensive data.

Currently, GSK has 9'000 people including 600 children in its H1N1 trials in Canada and Germany and it also encourages reporting from the millions of people who have taken the vaccine.

MOH recommends the CSL vaccine for expectant mothers as vaccines without additives have a longer track record of safety with pregnant women. A recent study published in the medical journal Lancet has also found vaccines without the additive to be more effective.

Dr Peiris cautioned that a new wave of infections next month would depend on the number of people in the community who had immunity through being infected or having the vaccine.

"If more than half have immunity, it will really dampen down the virus but it will still go along as it too is trying to find a way to survive," he said. "If it becomes resistant to Tamiflu, then we're in really bad shape if people particularly in the high risk groups, are not vaccinated."