Vaccinations are said to have saved more lives worldwide than any medical product or procedure in the past 50 years.
In a series of three articles, Priya Kulasagaran looks at the history of vaccines, how they work, the controversy surrounding immunisation programmes, and why they are still relevant.
If you lived a just a few hundred years ago, chances are that one of your biggest fears would be catching a fatal infectious disease.
Smallpox for example, was one of greatest scourges in human history. This disease, which starts with a distinctive rash that progresses to pus-filled blisters and can result in disfiguration, blindness, and death, first appeared in agricultural settlements in Africa around 10,000 B.C. It went on to ravage the world for centuries.
Thankfully, smallpox has been all but eradicated since 1979, thanks to a concentrated global effort and a miracle of modern medicine – vaccinations.
A history of vaccines
The discovery of the modern vaccine has been credited to British physician Edward Jenner. Experimenting with cowpox (a milder version of smallpox), Jenner successfully used material derived from cowpox pustules to create an immunity to smallpox in 1796. After proving to the scientific community that his methods worked, Jenner managed to receive massive support and funding to continue his vaccination efforts. Over the subsequent centuries, systematic implementation of mass smallpox immunisation culminated in its global eradication.
Jenner’s discovery of vaccination came from his observations that milkmaids who had contracted cowpox were immune to smallpox. But he was far from the first to notice this. As long ago as 429 BC, the Greek historian Thucydides observed that those who survived the smallpox plague in Athens did not become re-infected with the disease.
Meanwhile, Chinese physicians were the first to use a crude form of vaccination known as variolation. This was done by exposing healthy people to tissue from the scabs caused by smallpox – including inserting powdered scabs from smallpox pustules up the nose. In Africa and the Middle East, scrapings from smallpox pustules from a mildly infected individual were applied onto a scratch or a vein of a healthy person.
Variolation then spread to Europe and the Americas, and continued to be practised globally for centuries. It was even used by George Washington to safeguard the American army during their fight for independence against the English.
The middle of the 20th century was an active time for vaccine research and development. Methods for growing viruses in the laboratory led to rapid discoveries and innovations, including the creation of vaccines for polio. Researchers targeted other common childhood diseases such as measles, mumps, and rubella, and vaccines for these diseases reduced the disease burden greatly.
Now, with new DNA technology and delivery techniques, scientists are researching vaccines in even non-infectious diseases such as allergies and addictions.
How do vaccines work?
Simply put, vaccines act as a trial run for your body in protecting itself from certain types of bacteria and viruses. This so if the real version of the disease appears, your body would have already built the defences it needs to fight off the infection.
The white blood cells act as ‘protectors’ of your immune system, and can generally destroy germs that may cause problems in your body. However, some bacteria and viruses can trick these defences, and cause mild or severe infections.
Vaccines work by introducing a weakened or dead form of infection, known as the antigen. This antigen is derived from the pathogen, usually a disease-causing virus or bacteria. When developing this antigen, the must be altered to ensure it does not trigger the disease itself. In some vaccines, the antibody (the product of the immune system which helps the body fights antigen) is introduced.
The pathogen stimulates an immune response as if the body is encountering the disease – without causing the actual illness. This enables a quicker and more effective immune response upon future encounters with the disease-causing virus or bacteria. If left totally to chance, a child’s first exposure to a disease may be from a germ too strong for their immune system to fight.
While vaccination protects against a disease, it doesn’t always confer lasting protection. In cases where immunity has declined, administration of a ‘booster’ shot, or an extra administration of a vaccine following the earlier dose, helps to regain immunity. Example of vaccines that normally require follow-up booster shots include the oral polio vaccine (OPV) which persists for only 6 months and tetanus, which requires a booster shot every 10 years.
The power of the pack
Aside from protecting yourself, vaccination also helps protect a community as a whole from infectious diseases. When a high percentage of a population is vaccinated, it is difficult for a contagious disease to spread through the population. For example, if someone with measles is surrounded by people who are vaccinated against measles, the disease cannot easily be passed on to anyone, and it will disappear again. This is called ‘herd immunity’ or ‘community immunity’.
However, herd immunity only works if the majority of the population are vaccinated. This is important to protect people who are particularly vulnerable to disease, but cannot be safely vaccinated. This includes people such as newborn infants who are too young to be vaccinated; those with a weak or non-functioning immune system; the elderly; and those who are too ill to be vaccinated.
If the number of vaccinations in an area is low, it can cause a disease to spread rapidly through the community. With the diphtheria outbreak in Malaysia last year, the cases managed to be contained to certain families who chose not to immunise their children (leading to fatalities), as most of the country had received the required vaccination.
Previous evidence has shown that even if a disease is seemingly rare, we are still at risk of it if vaccinations are ceased. For instance, in 1974, 80% of Japanese children were vaccinated with pertussis (whooping cough) vaccine, and no deaths were recorded among the 393 cases of whooping cough that occurred that year. In contrast, when the vaccination rate dropped to 10% in 1979, 13,000 cases of whooping cough were recorded and 41 people died.
Recent research on new vaccines have begun to look at current diseases, such as malaria, the Zika virus and Ebola. It may take years yet for these to be effectively rolled out, and until then, our only hope to completely eradicate diseases such as smallpox, is to continue vaccinations on a wide-scale basis.
Malaysia’s immunisation programme currently includes 10 vaccines, some of which are combined shots to prevent several diseases. The chart below shows the ages at which children should be administered the relevant vaccinations, along with the diseases they help ward off.