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Human Immune System: What Is Immunity?

When a virus, bacteria, protozoa, fungus or toxin enters the body it is called an antigen. There are three types of immunity to antigens:

• Innate Immunity

• Acquired Immunity

• Passive Immunity

Innate immunity is the immunity all people start with such as a natural immunity to many antigens that make other animals sick. Your skin and mucous membranes are also an innate immunity healing quickly and destroying antigens. Acquired immunity improves through your immune response fighting antigens over your lifetime. Passive immunity generally refers to short term immunity “borrowed” by an infant through mother’s milk.

The body’s defense against antigens is called the “immune system”. The immune system is a network of cells, tissues and organs that constantly work together to protect the body.

The immune response is how the body fights an antigen. After the immune response the anti-bodies created to fight an antigen stay in your body forever. Generally, because of the antibodies, you only get sick once from one antigen. As you age and are exposed to more antigens your body develops more antibodies and you fall ill less often.

Immunologists use the body’s immune response to protect us from disease. They make an antigen that is like a certain disease, but does not cause illness called a vaccine. A vaccine makes your body produce new antibodies that kill the real disease when it is transmitted to you.

A vaccine shot or jab is called immunization or vaccination.

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Vaccine: How Long Do We Wait?

Influenza vaccines have been available for over 50 years. Generally, they are trivalent, i.e. they contain three different, inactivated virus strains, either whole viruses or parts or subunits of them. Because the flu virus is changing its antigenic shape constantly (either in minor drifts or major shifts), the composition of the flu vaccine needs to be adapted to these changes regularly. The monitoring of these changes is done by the Global Influenza Surveillance Network of the World Health Organization (WHO). At the beginning of each year, the WHO makes a recommendation for the strains to be included into the vaccine for the coming influenza season.

Traditionally, influenza vaccines are produced in fertilized chicken eggs. Eleven days after fertilization, the influenza virus—each strain is grown separately—is injected into the eggs and accumulates in the fluid surrounding the embryo. A high-yielding donor strain is co-injected. The embryo becomes infected so that the virus can multiply. After several days of incubation, machines open the eggs and harvest the virus. Then the virus is carefully purified, chemically inactivated and used to produce one dose of vaccine. On average, between one and two eggs are needed to produce one dose of vaccine. The entire process lasts at least six months.

The production of a vaccine therefore involves several steps:

1. Isolation of the virus

2. Acquisition of sufficient eggs for a production run

3. Actual egg-based production of the vaccine

4. Repeat of this process until supply meets demand

According to nature the global monovalent (one virus) vaccine production capacity is 450 million doses. This means six months lead time is needed to acquire the approximately 900 million necessary eggs for a single production run, roughly six months has to be allocated to a single production run and several production runs would be required to serve the demand of a global population of over 6 billion people. There is no doubt that in the event of a pandemic lasting several months there will not be adequate vaccine in adequate time.






Antivirals: What Hope Do They Offer?

In the face of a new virus that our immune system has no established defenses and the likelihood of vaccines not being available, the media and the public has latched onto anti-virals as the last resort.

The United States Food and Drug Adminstration has pointed out that some of the current influenza antiviral drugs are able to inhibit many of the "bird flu" viruses in the laboratory although it is not known exactly how much effect they would have against these infections in people.

There are four antiviral drugs currently approved by FDA to treat acute, uncomplicated influenza. Two related drugs, Symmetrel and Flumadine are approved for treatment and prevention of influenza A. Two newer drugs, Relenza and Tamiflu are approved for treatment of acute uncomplicated illness due to influenza A and B. Tamiflu has been approved also for preventive use, while Relenza is approved only for treatment. Approved ages, doses, and uses in children are different for each drug, so the individual package inserts should be checked for this information. The anti-influenza antiviral drugs are not a substitute for vaccine and are used only as an auxillary to vaccine in the control of influenza.

What does this all mean? It means that if you want Tamiflu to protect you against influenza you have to take it constantly. Once the Tamiflu runs out your protection runs out. If you want to use Tamiflu or Relenza as a treatment you have to take the antiviral for the prescribed number of days after the onset of symptoms and it will assist your immune system to fight off the virus. Again, since the human-to-human virus does not yet exist, it is not known if the anti-virals will work. In fact, the companies that manufacture these medications are currently seeking liability coverage if the medications do fail.






Antibiotics: Protection Against Complications?

The truth is, in the Spanish Flu epidemic most of the deaths were not due to uncomplicated influenza infection. Many of the deaths were due to secondary infections--typically bacterial and fungal—that caused pneumonia.

While antibiotics are hardly a silver bullet and they are useless against viruses, they raise the simple possibility of treatment for bacterial or fungal illnesses. Penicillin -- the first commercialized antibiotic -- was not discovered until 1929, 11 years too late to help when H1N1 gripped the world in 1918.

Unfortunately, the drawback with anti-biotics is that they will be exhausted in the first few weeks of a pandemic due to there being no adequate stockpiles to meet the surge in demand that would occur.