March 12, 2009
Flu fears - Cover story
One for all flu vaccine?
The idea - a global vaccine to squash out all flu viruses - is tantalising but such a drug is years away
By June Cheong
Picture this: No more yearly flu jabs and no more panic over a bird flu outbreak. Forget about a flu pandemic too.
Such optimism has followed a recent discovery by scientists of an Achilles' heel in a range of seasonal and pandemic Influenza A viruses.
The breakthrough occurred last month when researchers in California found an antibody, or infection-fighting protein, capable of neutralising certain Influenza A viruses - by sticking to them.
Because there seems to be a 'target area' common to these flu viruses for the antibody to attach itself to, scientists are hopeful of developing an effective, global flu vaccine.
That is the exciting news.
The more sobering news is that such a vaccine is still years away, which means the threat of a pandemic is still real.
'A flu pandemic appears delayed but current science cannot predict where, when or how,' said Associate Professor Leo Yee Sin, clinical director of the Communicable Diseases Centre at Tan Tock Seng Hospital.
The H5N1 bird flu virus remains a prime candidate for the next flu pandemic, medical experts heard at an international symposium on respiratory viral infections in Bangkok last month.
While comparatively few people worldwide have been infected with H5N1, the mortality rate from confirmed cases exceeds 60 per cent.
Humans are affected by three types of influenza viruses: Types A, B and C. It is Type A that can cause epidemics or pandemics as its subtypes can change suddenly or in a big way.
An epidemic refers to the appearance of more cases of a disease than normal in a community during a given timeframe while a pandemic is an epidemic that becomes very widespread .
The subtypes of Influenza A are classified by H and N components. There are 16 H components and nine N components. Of these, combinations of H1, H2 or H3 as well as N1 or N2 can infect humans.
Virus subtypes from H4 to H16 are seen only in animals - with the exception of H5N1.
Dr Leo said H3N3 was a common influenza virus in Singapore last year. The H1N1 virus has also been dominant here since 2008, said DrChan Kwai Peng, a virologist in the department of pathology at Singapore General Hospital.
Influenza viruses are composed of single-stranded ribonucleic acid (RNA). As these viruses do not have a second strand of genetic information to correct or back up changes in its only strand, mutations typically are 'make or break'.
Dr Leong Hoe Nam, a consultant infectious disease physician at SGH, said: 'It's an act of Mother Nature that viruses will continually change.
'Viruses are extremely promiscuous and their gene segments can exchange information quite easily.'
If there is a big enough antigenic drift, which is an accumulation of mutations within the virus, the virus can become a new strain.
An antigenic shift can also occur whereby the coming together of two viral strains results in a new virus. Antigenic shift only occurs with Influenza A viruses.
This is why bird and human flu viruses can exchange genes, creating highly virulent new viruses.
The 1957 Asian flu pandemic and the 1967 Hong Kong flu pandemic were caused by the reassortment of circulating human Influenza A viruses with an avian virus.
Pandemic flu occurs when a new virus appears and spreads as easily as normal flu.
Humans will have no immunity against a pandemic virus as the virus is new.
Still, other conditions have to be met before a pandemic occurs.
Dr Leong said: 'Even if a new virus emerges, it needs a suitable host. And after finding a suitable host, the virus needs the host to be able to transmit it.'
An Agri-food & Veterinary Authority of Singapore (AVA) spokesman said that while there is a probability the H5N1 virus may acquire the ability to transmit efficiently between humans, resulting in a pandemic, it is so far still an avian virus.
To control the disease and prevent it from entering Singapore, AVA has adopted a multi-pronged approach.
It bans the import of birds and avian products from any country with avian flu outbreak and maintains constant surveillance on all consignments of live poultry and birds.
AVA also surveys and checks local poultry slaughterhouses and poultry and bird farms to ensure that they have measures like complete perimeter fencing around the farm.
Should avian influenza reach our shores, AVA has plans for cluster culling of poultry farms here.
Moreover, the Government is spending about $50 million to stockpile 1.7 million courses of Tamiflu and 50,000 courses of Relenza, which can treat 25 per cent of the population.
Tamiflu and Relenza are both anti-viral medicine for flu treatment and prevention. However, resistance to the former has been growing.
A new study in the Journal Of The American Medical Association found 98.5per cent of the H1N1 influenza virus circulating in the United States is now resistant to Tamiflu.
Asked if the stockpile of Tamiflu would thus be useless in a possible pandemic, DrJeffery Cutter, a senior consultant in the communicable diseases division at the Ministry of Health, said: 'It is unlikely that a future pandemic flu virus would be resistant to the drug from the beginning. A pandemic flu virus would be very different from the current circulating strains of flu and so would not be expected to have the resistant gene found in the H1N1 subtype.
'With widespread use during a flu pandemic, resistance to Tamiflu would gradually increase. We are studying whether to supplement the stockpile with additional doses of Relenza.'
Relenza works well against current flu strains but its method of drug delivery - inhalation - is more cumbersome and not suitable for children, those with asthma, breathing problems or milk allergies.
Dr Leong said: 'It's worrying for us physicians. What Man thinks we can conquer, Nature defies. We're in true need of a good medicine.'
Pre-pandemic vaccines like vaccines for bird flu, which became available two years ago, have pointed the way forward as they have the potential to reduce the number and severity of cases. Another alternative is for people to get vaccinated against normal flu so that even if they do catch bird flu, the two strains do not mix.
Singapore is buying 2.6 million doses of the bird flu vaccine, which will be delivered over a three-year period.
Looking forward, the experts are working to realise the tantalising possibility of an international flu vaccine.
Primed for new flu virus
The next flu pandemic is coming, we are told. But what happens next is mostly unknown.
Dr Leong Hoe Nam, a consultant infectious disease physician at Singapore General Hospital, said: 'The whole world is just primed for the next flu pandemic, what with globalisation and easy travel.'
It will happen when a new flu virus turns up and spreads efficiently from person to person.
A pandemic virus can emerge either through genetic mutation or the interaction between a seasonal influenza virus and an animal influenza virus.
The 20th century saw three flu pandemics: the 1918 Spanish influenza, the 1957 Asian influenza and the 1967 Hong Kong influenza. The latter two were less severe.
However, the Spanish influenza saw 500 million people, or 40 per cent of the world population then, infected. At least 50 million people died.
In colonial Singapore, it killed 2,870 people out of a population of 370,000.
Some medical experts estimate that up to 350 million people could die from the next flu pandemic.
Treatment options for a flu pandemic are anti-viral medication, pre-pandemic vaccines, pandemic vaccines and seasonal influenza vaccines.
However, only a pandemic vaccine can be tailored specifically to the newly emerged influenza strain. The catch? It cannot be produced until after the virus has popped up.
It is estimated to take four to six months for the first such vaccines to be ready and available.
As Singapore does not have the capacity to manufacture vaccines, the wait time may be closer to between nine and 12 months. This being the case, the Government will swing into action with anti-virals and non-medical measures.
These include closing places like schools and malls to reduce human traffic and infection transmission, isolation of infected people and a stress on personal hygiene.
In an epidemic, people need to vaccinate themselves against the flu and avoid crowds and crowded places, said Associate Professor Leo Yee Sin, clinical director of the Communicable Diseases Centre at Tan Tock Seng Hospital.
The Ministry Of Health (MOH) said a pandemic may come in multiple waves, each lasting six weeks. Waves may happen either in the same year or in successive influenza seasons.
An infected person will be infectious a day before the onset of influenza symptoms until three to five days after their onset. Children will shed more virus and be infectious for up to three weeks. An infected person will probably spread the virus to two others.
MOH estimates that 25 per cent of Singapore's population may become infected. However, the Government wants to prevent the pandemic virus from even landing here and it has in place contingency plans, such as stepped-up border restrictions.
If a pandemic takes hold, the Government will take steps like tracking and containing the outbreak, isolating influenza cases, treating patients with anti-virals and vaccines, and closing public places.
For more information on MOH's influenza pandemic response plan, log onto www.crisis.gov.sg
PRECAUTIONS TO TAKE
Taking individual responsibility for your own action and behaviour is vital in a pandemic.
Emphasising this, Dr Leong Hoe Nam, a consultant infectious disease physician at Singapore General Hospital, said: 'If you're unwell, you should not go out and you should avoid crowded places.'
Ministry of Health (MOH) guidelines advise good hygiene practices like washing one's hands often, covering the nose and mouth with a tissue when coughing or sneezing and not spitting on the floor.
People aged 65 and above, those with chronic heart or lung disease or diabetics, children and teenagers on long-term aspirin therapy and pregnant women should get the influenza jab, MOH added.
Besides these general ground rules, Mind Your Body finds out about some of the precautions certain groups of people should take.
Children
§ Those sick with influenza should be excused from school.
§ They should wash their hands regularly and with soap.
§ Toys should be kept clean and disinfected regularly.
§ Body fluid spills like vomit must be cleaned thoroughly before the spot is disinfected. Mops and cloths used to clean the spill should be soaked in disinfectant solution after use and rinsed with water.
At work
§ Practise good personal hygiene like washing hands often and thoroughly.
§ Start temperature screening for visitors and regular temperature checks for staff.
§ Learn about the ways the flu can be transmitted and how to prevent it.
§ More frequent cleaning and disinfection of work areas.
§ Establish a contact tracing system so that if someone falls ill, the authorities can easily track who he has come into contact with.
Travellers
§ A flu jab is essential, especially for high-risk groups like those aged 65 and above, diabetics and people with chronic heart and lung disease.
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