Reading - Part 5

How Vaccines Work

For more than two hundred years, vaccines have been one of the most powerful tools in modern medicine. They have helped people live longer, healthier lives by preventing diseases that once killed millions. To understand how vaccines work, it is useful to first look at how the human immune system protects the body, what happens when a vaccine is given, and why vaccines are so important for both individuals and communities.

The human body has a defense system called the immune system. Its main job is to protect us from harmful invaders, such as viruses and bacteria. When these invaders, also known as pathogens, enter the body, the immune system recognizes them as dangerous and starts fighting. One of the most important parts of the immune system is the white blood cells. These cells move through the bloodstream and tissues, always searching for signs of infection. When they detect a virus or bacterium, some white blood cells attack and destroy the invaders directly, while others create special proteins called antibodies. Antibodies are like tiny weapons that attach to the virus or bacterium, making it easier for the body to remove it.

An important feature of the immune system is memory. After fighting an infection once, the immune system "remembers" the invader. If the same pathogen enters the body again, the immune system responds faster and more effectively, often stopping the disease before it can make a person sick. This natural memory is what vaccines use to give us protection.

A vaccine is a medical product that trains the immune system without causing the actual disease. It works by showing the body a safe version of a pathogen. This can be done in several ways. Some vaccines use pathogens that are killed so they cannot cause disease. Others use a version of the virus or bacterium that is alive but weakened. Some vaccines include only parts of the pathogen, such as proteins on its surface. In recent years, new vaccines have been made with mRNA, which gives the body instructions to make a harmless piece of the pathogen’s protein so the immune system can learn to recognize it.

When a person receives a vaccine, usually by injection, their immune system reacts as if it were facing a real infection. White blood cells create antibodies and memory cells. However, because the vaccine is not dangerous, the person does not experience the severe symptoms of the actual disease. Later, if the real pathogen tries to attack, the immune system is ready to fight it quickly.

Before vaccines existed, infectious diseases caused enormous suffering. Smallpox, for example, killed millions of people for centuries. In the 20th century alone, smallpox caused more than 300 million deaths. Thanks to vaccines, smallpox was completely eliminated in 1980, the first disease in history to be wiped out by human effort. Other diseases, such as polio, measles, and diphtheria, have also been greatly reduced by vaccination campaigns. In many countries today, children rarely see these illnesses, which were once common and deadly.

Vaccines not only protect individuals but also communities. This is because of a concept called herd immunity. When enough people are vaccinated, the disease has little chance to spread. This protects those who cannot receive vaccines, such as newborn babies or people with certain medical conditions.

Some people worry about the safety of vaccines. Like any medicine, vaccines can have side effects. These are usually mild, such as a sore arm or a slight fever. Serious side effects are extremely rare. Scientists and doctors carefully test vaccines before they are approved, and they continue to monitor them to make sure they remain safe. Another question people often ask is why we sometimes need booster shots. The reason is that immune memory can fade over time. For some diseases, like measles, one or two doses are enough to provide lifelong protection. For others, like tetanus or COVID-19, booster doses may be needed to keep the immune system strong.

Vaccines are not only for children. Adults also benefit from them. For example, older people often receive vaccines against influenza or pneumonia, because their immune systems are weaker. Travelers may need vaccines before visiting certain countries where diseases such as yellow fever are present. In recent years, new technologies have made it possible to develop vaccines more quickly. The COVID-19 pandemic showed how important this can be. Scientists created safe and effective vaccines in less than a year, something that would have seemed impossible in the past. These vaccines helped reduce severe illness and death worldwide. At the same time, the pandemic also showed the challenges of vaccine distribution. In some places, vaccines were not available for everyone at the same time. This highlighted the need for global cooperation, since diseases can easily cross borders.