WEBLOG DO FRAGA

Sunday, May 10, 2009

Swine flu vacine

10 may 2009--The World Health Organization says that work on a vaccine for swine flu began as soon as the first human case of the virus became known. It estimates that the first doses of the vaccine will be available five to six months from now.

People who have had swine flu seem to be recovering. Why do we need a vaccine for it?

Although most people who have had swine flu seem to be recovering well, some people have died. Seasonal flu vaccines are important for the elderly and people with weakened immune systems, as they are particularly susceptible to complications like pneumonia.

The vaccine is also needed in case swine flu continues to spread, especially in case it becomes more of a problem over winter, which is peak flu season.

Will existing vaccines work for swine flu?

The WHO says that current evidence (while incomplete) suggests that seasonal influenza vaccines will offer little or no protection against swine flu.

Each year a new batch of flu vaccine is made to match the strains that the WHO decides will be most likely to circulate that winter, which is the peak flu season.

The influenza virus comes in many different strains that all have slightly different proteins on their surfaces. The body’s defences can only attack and destroy a virus if they recognise these proteins and, therefore, antibodies that recognise one strain may not recognise other strains.

If the proteins on the surface of the swine flu strain are highly similar to those of the strains used to create previous vaccines, then previous vaccines may provide some protection against swine flu. The NIBSC says that it is looking at the swine flu virus (an H1N1 strain of influenza A) and past H1N1 seasonal vaccines to determine if this is the case.

When will a vaccine be ready for swine flu?

Vaccines are prepared after a virus emerges, as the virus itself is the starting material for vaccine production. Therefore, there is always a time lag while a vaccine is prepared.

Vaccine preparation involves multiple steps. Therefore, it can take several months for a vaccine to be ready.

The WHO estimates that the virus for making the vaccine will be available to vaccine manufacturers by mid-May, and the first doses of a new vaccine could be available five to six months after this, but may take longer if the virus strain used to make the vaccine grows slowly in the laboratory.

Will the vaccine work for all cases of swine flu?

Vaccination is very effective in preventing and reducing the impact of serious illness. However, vaccines are not 100% effective and could become less effective if the virus mutates. Current flu vaccines last for about a year and give about 70-80% protection against infection with strains of influenza virus that are very similar to those used to make the vaccine.

The WHO says that it is too early to predict how the influenza A(H1N1) virus might change. The WHO is closely monitoring the virus for changes, and this will help countries to make a quick response if the virus undergoes important changes.

What is the difference between vaccines and antivirals?

Vaccines prepare the body to fight against certain diseases, in case it comes into contact with them in the future.

Antiviral drugs tend to be used in people who have already been exposed to a virus or are already known to be infected with a virus. Different antiviral drugs work in different ways, but generally they stop the virus from making new viruses and from spreading from cell to cell in the body.

Vaccines can be given long before exposure to an infectious agent and give people long-lasting protection against that agent. Antivirals are only effective if given within a specific time before or after exposure to the virus and only give protection while they are being used.

What is a vaccine?

A vaccine prepares the body to fight against certain infectious diseases in case we come into contact with them in the future. It does this by prompting the immune system to produce antibodies against them. Antibodies are proteins produced by the immune system to help identify and destroy disease-causing organisms such as viruses and bacteria.

Vaccines are usually made from tiny amounts of the disease-causing organism that have been killed or weakened. By introducing them to the body, the immune system can be trained to recognise these organisms in future and rapidly produce antibodies to fight them off.

How is a vaccine made?

To make a vaccine, a large amount of the virus or bacteria is needed. In the case of swine flu, the US Centers for Disease Control and Prevention (CDC) began isolating and preparing strains of the swine flu virus as soon as the first human case became known. These strains were sent to its counterparts in other countries including the National Institute for Biological Standards and Control (NIBSC) in the UK. These organisations prepare the virus strains to be used in making the vaccine.

Viruses can be grown in hens’ eggs, but often the infectious influenza virus strains do not grow well in eggs. To get around this, the infectious virus is injected into the eggs with another influenza virus that thrives in eggs. The two viruses swap pieces of their genetic material and produce hybrids, some of which both grow well in hens’ eggs and also have the elements of the disease-causing virus needed for a vaccine. These hybrids are isolated and the best candidate for making a vaccine is selected. This chosen hybrid strain is then grown and distributed to vaccine manufacturers.

The vaccine manufacturers use dead or weakened virus to create the vaccine. Other constituents can also be added to the vaccine, such as a suspending fluid to carry the virus into the body, preservatives and stabilisers that allow the vaccine to be stored safely, and chemicals to help the vaccine to promote an immune response.

Who usually gets vaccinated for flu?

People who are most likely to suffer from complications usually get vaccinated for seasonal flu. This includes:

people aged 65 years and over,
people with certain long-term medical conditions, such as chronic respiratory, heart, renal, or neurological disease, diabetes mellitus or immunosuppression,
health and social care professionals, and
poultry workers (to reduce the risk of being infected with both human and avian flu at the same time).

The recommended groups for vaccination with any new swine flu vaccine may be different.