Is it possible to create a vaccine effective against all or most flu viruses? Until recently the anwser would be “No.” A new discovery gives us a glimpse of hope. Human immune system can effectively fight flu, it can produce antibodies, which block viruses. However, it takes time to recognize a threat, to identify it exactly and to produce the effective weapon – antibodies targeted at a particular virus. While the immune system is busy with preparation to the counterattack, viruses have enough time to reproduce and to cause very unpleasant symptoms, which may be lethal for some (or many) people. Vaccines, which are typically viruses made unviable by some or other means, but with intact molecules of their capsules, can prepare the immune system to much faster reaction upon a massive invasion of real viruses. There are 3 types of flu viruses. Type A can develop in birds (mainly aquatic birds) and in humans. This is the most common cause of flu. Type B can affect only people, and it is rather rare. Type C can affect humans and pigs, it is rather common, but not as common as type A. Basically a virus is a capsule made of proteins and containing the genetic code of the virus – RNA or DNA molecules. A virus attaches itself to a healthy cell and injects its genetic code into it. After this, the cell begins to reproduce the genetic code and proteins of the virus, which recombine in new viruses. In this process the cell poisons itself with byproducts of reproduction and eventually dies. The newborn viruses spread around the body and find themselves new cells. Antibodies target protein molecules of the capsule of a virus, block them and neutralize the virus. But here is a problem. The antibody and the protein must fit like a key and a lock. Two kinds of proteins form the capsule of a flu virus – hemagglutinin (H) and neuraminidase (N). There are 16 known subtypes of H proteins and 7 known subtypes of N proteins in type A influenza alone. Antibodies that block molecules of one of the subtypes are harmless for other subtypes. Usually vaccines are made to train immune system to produce antibodies targeting H proteins. But it is not possible to make a vaccine protecting from all kinds of flu viruses. Scientists try to guess which types of viruses may spread next winter, but often their forecasts are wrong, and vaccination becomes ineffective. There are vaccines that combine two or even three strains of viruses, but still they have a big chance to miss the target. The problem is that you have to produce enough doses of vaccine and to conduct massive vaccination before an outbreak of flu, and when it happens, it is already too late to change anything. It is not possible to produce a billion doses of vaccine quickly. In a recent research work, which included observation and detailed blood tests of people, who had flu in the past several years, a new fact about human antibodies targeting the H molecules was found. It appeared that there are two types of antibodies attacking this molecule. And the molecule itself consists of two parts – the head and the stem. In different variations of H molecules the heads are different, while the stem is the same. In mutations of flu, which occur every year or even more frequently, stems remain unchanged for decades. Currently existing vaccines train antibodies targeting the heads of H molecules. This discovery gives scientists an idea to train antibodies, which would attack stems of the molecules. If it is possible, than a single vaccine can be effective against many kinds of viruses, practically against all of them, and will remain effective for a decade or more. When can we expect such vaccines? Scientists believe that not sooner than in a decade from now. It is not yet known if blocking only the stems of H molecules will be sufficiently effective, it is not yet known how to train antibodies of this type and how to make a vaccine, which will train these antibodies. After all these studies, several years of medical tests will be needed. If scientists succeed and this new type of vaccine will be produced, will it help to eradicate flu as it was done with smallpox and polio viruses? No, because type A and type C can exist not only in humans. They germinate in birds and pigs and then suddenly jump onto humans. Only type B can be eradicated.
Posted on: Sun, 08 Sep 2013 09:44:31 +0000
Trending Topics
Recently Viewed Topics
© 2015