Vaccination is a simple, safe, and effective way of protecting people against harmful diseases, before they come into contact with them. It uses your body’s natural defenses to build resistance to specific infections and makes your immune system stronger.
Vaccines train your immune system to create antibodies, just as it does when it’s exposed to a disease. However, because vaccines contain only killed or weakened forms of germs like viruses or bacteria, they do not cause the disease or put you at risk of its complications.
Most vaccines are given by an injection, but some are given orally (by mouth) or sprayed into the nose.
Vaccination is a safe and effective way to prevent disease and save lives – now more than ever. Today there are vaccines available to protect against at least 20 diseases, such as diphtheria, tetanus, pertussis, influenza and measles. Together, these vaccines save the lives of up to 3 million people every year.
When we get vaccinated, we aren’t just protecting ourselves, but also those around us. Some people, like those who are seriously ill, are advised not to get certain vaccines – so they depend on the rest of us to get vaccinated and help reduce the spread of disease.
Vaccines reduce risks of getting a disease by working with your body’s natural defenses to build protection. When you get a vaccine, your immune system responds. It:
The vaccine is therefore a safe and clever way to produce an immune response in the body, without causing illness.
Our immune systems are designed to remember. Once exposed to one or more doses of a vaccine, we typically remain protected against a disease for years, decades or even a lifetime. This is what makes vaccines so effective. Rather than treating a disease after it occurs, vaccines prevent us in the first instance from getting sick.
Vaccines work by training and preparing the body’s natural defences – the immune system – to recognize and fight off viruses and bacteria. If the body is exposed to those disease-causing pathogens later, it will be ready to destroy them quickly – which prevents illness.
When a person gets vaccinated against a disease, their risk of infection is also reduced – so they’re also less likely to transmit the virus or bacteria to others. As more people in a community get vaccinated, fewer people remain vulnerable, and there is less possibility for an infected person to pass the pathogen on to another person. Lowering the possibility for a pathogen to circulate in the community protects those who cannot be vaccinated (due to health conditions, like allergies, or their age) from the disease targeted by the vaccine.
'Herd immunity', also known as 'population immunity', is the indirect protection from an infectious disease that happens when immunity develops in a population either through vaccination or through previous infection. Herd immunity does not mean unvaccinated or individuals who have not previously been infected are themselves immune. Instead, herd immunity exists when individuals who are not immune, but live in a community with a high proportion of immunity, have a reduced risk of disease as compared to non-immune individuals living in a community with a small proportion of immunity.
In communities with high immunity, the non-immune people have a lower risk of disease than they otherwise would, but their reduced risk results from the immunity of people in the community in which they are living (i.e. herd immunity) not because they are personally immune. Even after herd immunity is first reached and a reduced risk of disease among unimmunized people is observed, this risk will keep falling if vaccination coverage continues to increase. When vaccine coverage is very high, the risk of disease among those who are non-immune can become similar to those who are truly immune.
World Health Organisation (WHO) supports achieving 'herd immunity' through vaccination, not by allowing a disease to spread through a population, as this would result in unnecessary cases and deaths.
For COVID-19, a new disease causing a global pandemic, many vaccines are in development and some are in the early phase of rollout, having demonstrated safety and efficacy against disease. The proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity is not known. This is an important area of research and will likely vary according to the community, the vaccine, the populations prioritized for vaccination, and other factors.
Herd immunity is an important attribute of vaccines against polio, rotavirus, pneumococcus, Haemophilus influenzae type B, yellow fever, meningococcus and numerous other vaccine preventable diseases. Yet it is an approach that only works for vaccine-preventable diseases with an element of person-to-person spread. For example, tetanus is caught from bacteria in the environment, not from other people, so those who are unimmunized are not protected from the disease even if most of the rest of the community is vaccinated.
The most commonly used vaccines have been around for decades, with millions of people receiving them safely every year. As with all medicines, every vaccine must go through extensive and rigorous testing to ensure it is safe before it can be introduced in a country.
An experimental vaccine is first tested in animals to evaluate its safety and potential to prevent disease. It is then tested in human clinical trials, in three phases:
Once the results of clinical trials are available, a series of steps is required, including reviews of efficacy, safety, and manufacturing for regulatory and public health policy approvals, before a vaccine may be introduced into a national immunization programme.
Following the introduction of a vaccine, close monitoring continues to detect any unexpected adverse side effects and further assess effectiveness in the routine use setting among even larger numbers of people to continue assessing how best to use the vaccine for the greatest protective impact.
All the ingredients of a vaccine play an important role in ensuring a vaccine is safe and effective. Some of these include:
Vaccine ingredients can look unfamiliar when they are listed on a label. However, many of the components used in vaccines occur naturally in the body, in the environment, and in the foods we eat. All of the ingredients in vaccines – as well as the vaccines themselves - are thoroughly tested and monitored to ensure they are safe.
Vaccination is safe and side effects from a vaccine are usually minor and temporary, such as a sore arm or mild fever. More serious side effects are possible, but extremely rare.
Any licensed vaccine is rigorously tested across multiple phases of trials before it is approved for use, and regularly reassessed once it is introduced. Scientists are also constantly monitoring information from several sources for any sign that a vaccine may cause health risks.
Remember, you are far more likely to be seriously injured by a vaccine-preventable disease than by a vaccine. For example, tetanus can cause extreme pain, muscle spasms (lockjaw) and blood clots, measles can cause encephalitis (an infection of the brain) and blindness. Many vaccine-preventable diseases can even result in death. The benefits of vaccination greatly outweigh the risks, and many more illnesses and deaths would occur without vaccines.
Like any medicine, vaccines can cause mild side effects, such as a low-grade fever, or pain or redness at the injection site. Mild reactions go away within a few days on their own.
Severe or long-lasting side effects are extremely rare. Vaccines are continually monitored for safety, to detect rare adverse events.
Source : WHO
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