Vaccines and therapies for infectious diseases have saved many lives. Control of many infectious diseases has been one of medicine’s greatest accomplishments. Before the 20th century, infectious diseases were uncontrollable and a constant danger.

Vaccines

Vaccines are not cures for diseases. They are preventative measures against a disease, and they help healthy people stay healthy. Vaccines help protect you from illnesses spread by microorganisms such as bacteria and viruses that cause illness.

A vaccine is a substance that provides immunity to disease. Vaccines can be made from weakened or dead pathogenic microorganisms or a specific part of the bacteria or virus (antigen). Scientists are also learning how to make synthetic molecules that resemble molecules from the pathogenic microorganism. These adjuvants strengthen existing vaccines helping to stimulate (kick start) the immune system.

Immunisation is the process of being vaccinated with a vaccine and becoming immune to the disease. The vaccine stimulates your immune system to make memory cells that will give you protection against that particular disease in the future. If the disease does reappear, these memory cells rapidly make antibodies, which identify and neutralise antigens (pathogenic substances), allowing your body to eliminate the disease immediately before it can do you any harm.

Not just for your protection

Vaccines are not just for your own protection. Getting vaccinated/immunised yourself helps protect the people around you. It keeps you from spreading a serious disease to anyone who is not vaccinated. People not in good health, babies and pregnant women are often not vaccinated because their immune systems may not respond to the vaccine effectively anyway. By choosing to get vaccinated, you may decrease their risk of getting a disease or infection, as well as yours.

Getting vaccinated helps to stop epidemics and pandemics. Some dangerous diseases that once killed huge numbers of people have been stopped or are controlled because of vaccines. For example, polio was a common childhood illness in New Zealand mid last century. However, as a result of immunisation, polio has disappeared from New Zealand and most parts of the world – in 2000, the Western Pacific region was declared polio free.

However, diseases may reappear if people stop being vaccinated. This has recently happened with tuberculosis (TB), which is making an appearance globally. The old vaccine for TB is not so effective either, so scientists are exploring new ways of making a more effective TB vaccine.

Although vaccines exist for all sorts of diseases, both viral and bacterial, some diseases cannot be contained by them. The common cold and influenza are two examples. These diseases either mutate so quickly or have so many different strains in the wild that it is impossible to inject all of them into your body. Each time you get the flu, for example, you are getting a different strain of the same disease.

Therapies

Therapies are the range of measures that can be used to help the body’s natural defences fight off infectious diseases. They strengthen the immune system to do its job. These include medications (drugs), vitamins, healthy eating, exercise, rest and so on.

Antibiotics were originally substances derived from living microorganisms that inhibit the growth of other microorganisms. They work either by destroying bacteria or by preventing them from multiplying. Penicillin, for example, comes from a living mould (Penicillium fungi) and destroys the cell wall of susceptible bacteria. It was the first antibiotic to be mass produced and saved hundreds of soldiers’ lives when it became available in the early 1940s. Some of the antibiotics in use today are man-made.

Unfortunately, antibiotics do not destroy viruses. As a result, viruses are responsible for many of the serious (and often fatal) infectious diseases today. Although no real cures have been developed for viruses to date, some antiviral treatments are available and others are being developed. These prevent the virus multiplying and cause the illness to run its course more quickly, for example, acyclovir (Zovirax) used to treat herpes and Tamiflu used to treat H1N1 (swine) flu.

For the future

Scientists are continually researching for new ways to help the immune system destroy infectious diseases. New and innovative vaccines and drugs (that are synthetic rather than using actual disease microorganisms) are being worked on, but they take many years to produce. It can take 20–30 years to produce a new vaccine or drug because of the huge amount of testing needed.

Once scientists consider they might have a new drug or vaccine, it needs to be tested rigorously. First, it may be tested on animals, then it gets tested on a few volunteers. If it still works well, it’s tested on a slightly larger group of people. Finally, it’s tested on large population groups before it can be sold on the market. All of this takes a very long time and a lot of money. One vaccine can cost about $2 billion to develop by the time it reaches the market.

    Published 3 November 2010