The flu and the science of ultimate vaccine

The Swine Flu virus is round and about, sporadically taking its toll in countries of the world. The number of cases is Bangladesh is also rising day by day. As if the world hasn't already had enough of plague from mice, the Mad Cow Disease and then the Bird Flu! So one can rightfully ask, "A flu is no big deal. Then why are people all of a sudden talking about a pandemic?" The answer ultimately comes down to evolution.
Flu is such a successful virus that each year almost everyone on Earth is exposed, and about a third of us get sick. It kills between 50 and 200 people per million every year, especially the elderly. Flu can kill in several ways. It can destroy your lungs or damage them so much that bacteria run riot and finish the job. Your immune response to the virus can trigger a crisis such as a heart attack or even spiral out of control and kill you. Of course, most flu strains, including (so far) the 2009 pandemic virus, cause only mild symptoms in the vast majority of people.
The reason flu keeps infecting us again and again is that the virus is constantly changing (or evolving). The first time you get infected, your immune system has to rely initially on innate, non-specific defences. But it also evolves specific defences, learning to make antibodies and immune cells that recognise that particular virus and destroy both it and any cells it has infected. This process can take a week or more, but once we have defences against a virus, we can respond to it much more quickly next time. This is why many viruses, such as measles, make us ill only once.
Flu viruses, however, evolve so fast that this "immune memory" provides only partial protection. Most of the antibodies we produce bind to the globular heads of a surface protein on the virus called haemagglutinin (H) and neuraminidase (N). That's why you will notice flu viruses have names with a combination of these two letters, eg. H5N1 for a bird flu virus and the latest H1N1 for swine flu virus.
As flu viruses circulate through the human population, some acquire small mutations in haemagglutinin and neuraminidase that alter their shape and prevent our existing antibodies from binding as strongly. If the differences are large enough, we can be infected by one of these new strains, although our symptoms will be milder than if we had no previous immunity to flu at all.
And so it goes on. By staying one step ahead of our immune systems, the flu virus can infect large numbers of people year after year. What's more, every few decades a flu strain acquires a new haemagglutinin - by swapping genes with a pig or bird flu strain for example, that is very different from those most people have immunity to, so we have very little protection. This is when the flu goes pandemic.
The swine flu viruses are said to have acquired their genes from a combination of four kinds of influenza viruses one endemic in humans, one endemic in birds and two endemic in pigs. Transmission of the new strain is human to human. The virus typically spreads from coughs and sneezes or by touching contaminated surfaces and then touching the mouth or nose. Symptoms include fever, sneezes, sore throat, coughs, headaches and muscle or joint pains.
Existing flu vaccines all work by mimicking natural infections. Antibodies made in response to vaccination with one strain of influenza viruses can provide protection against different, but related strains.
Based on global monitoring of flu strains, virologists try to predict which haemagglutinin and neuraminidase will dominate during the next flu season. The annual vaccines contain inactivated flu viruses bearing these specific proteins. If the virologists guess right, the vaccine will protect you until the virus changes enough again. A less than ideal match may result in reduced vaccine effectiveness against the variant viruses, but it still can provide enough protection to prevent or lessen illness severity and prevent flu-related complications.
In addition, it is important to remember that the influenza vaccine contains three virus strains so the vaccine can also protect against the other two viruses. For these reasons, even during seasons when there is a less than ideal match, influenza vaccination is recommended.
Researchers are working on an entirely new class of antiviral drugs that should do something seemingly impossible: work against a wide range of existing viruses and also be effective against viruses that have not even evolved yet. What's more, it should be extremely difficult for any virus to become resistant to these drugs.
This might sound too good to be true, but the first trials of these drugs are already producing encouraging early results. If just a few of them live up to their promise in full-scale human trials, they could be a medical breakthrough on a par with the discovery of penicillin. At last, doctors will be able to treat viral diseases as ably as they do bacterial ones.
The conventional strategy for developing antivirals is "one bug, one drug" - finding a drug that blocks viral replication by binding to part of a viral protein. The trouble is -- any minor mutation that slightly changes the shape of the protein can render these drugs useless, as is happening with the Tamiflu drug.
Researchers are trying to make use of the fact that by themselves, viruses are more helpless than newborn babies. They can replicate only by tricking their host cells (our own organ cells) into making more copies of them, a process that can involve hundreds of host proteins. Therefore, disabling these proteins should block viral replication without killing healthy cells.
Another concept researchers are working on is to shift the target from the more vulnerable parts of the virus. There are conserved proteins that are almost identical in all flu, because they are delicate bits of machinery that do complex tasks and can't really change much. If we can shift the immune system to attack the conserved proteins instead, flu cannot mutate to escape without crippling its own machinery.
Whether these experiments will work out or not, only time will tell. However, ironically, full scale human trials of the new concepts have currently been stalled as the world is trying to deal with swine flu.
So what cures are available at this point? At this point, antiviral drugs that inhibit neuraminidase such as Tamiflu and Relenza do help to a certain extent by shortening the duration of symptoms. They do so by slowing viral replication, giving the immune system more time to kick in. That makes flu symptoms less severe, which could make the difference between life and death in a pandemic. However, there is some amount of controversy on the certain side effects of Tamiflu. In Bangladesh, officials believe there is a good stock of flu drugs and it is possible to make more within the country.
At individual level, you are recommended to cover coughs and sneezes and wash your hands a lot. Don't run down your ability to fight infection eat plenty of fruit and vegetables, exercise and get enough sleep. Some scientists recommend going on statins. These drugs are for lowering cholesterol. But there is very preliminary evidence that they might protect against the general inflammatory reaction caused by flu, which can trigger heart attacks or strokes. A Dutch study of several thousand people aged 60 or more found there was no surge in deaths during the flu season among those on statins.
If the pandemic is far worse than feared, or if you plan to isolate yourself during a pandemic, you will need emergency supplies of food, water and fuel. Companies should prepare for many workers being absent and, where possible, set up systems that allow people to work from home.
Most countries in the world have pandemic plans, on paper at least. They can respond with vaccines, drugs, and measures called "social distancing", aimed at limiting human contacts that spread flu. Mexico has already done this, by banning public gatherings and closing schools in affected areas. Modelling suggests this can be effective. The Bangladesh government should consider doing the same should the matter seem to be going out of hand. Already, a few English medium schools in Bangladesh have been declared closed until further notice to avoid spread of the virus among students.
Bangladesh has already started screening inbound travelers for swine flu at the Zia International Airport as well as sea ports, etc. Doctors and the officials of the airport have been given training so that they can detect the virus. However, more awareness could be spread among the public regarding swine flu and preventive measures against it through television, rallies and other such forms of mass communication.