Immunization is a global health and development success story, saving millions of lives every year. Vaccines reduce risks of getting a disease by working with your body’s natural defences to build protection. When you get a vaccine, your immune system responds.
We now have vaccines to prevent more than 20 life-threatening diseases, helping people of all ages live longer, healthier lives. Immunization currently prevents 2-3 million deaths every year from diseases like diphtheria, tetanus, pertussis, influenza and measles.
Immunization is a key component of primary health care and an indisputable human right. It’s also one of the best health investments money can buy. Vaccines are also critical to the prevention and control of infectious-disease outbreaks. They underpin global health security and will be a vital tool in the battle against antimicrobial resistance.
Yet despite tremendous progress, far too many people around the world – including nearly 20 million infants each year – have insufficient access to vaccines. In some countries, progress has stalled or even reversed, and there is a real risk that complacency will undermine past achievements.
Global vaccination coverage – the proportion of the world’s children who receive recommended vaccines – has remained the same over the past few years.
You can find additional information from the World Health Organisation below, in answer to common questions about vaccines and immunisations.
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.
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.
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.
Without vaccines, we are at risk of serious illness and disability from diseases like measles, meningitis, pneumonia, tetanus and polio. Many of these diseases can be life-threatening. WHO estimates that vaccines save between 2 and 3 million lives every year.
Although some diseases may have become uncommon, the germs that cause them continue to circulate in some or all parts of the world. In today’s world, infectious diseases can easily cross borders, and infect anyone who is not protected
Two key reasons to get vaccinated are to protect ourselves and to protect those around us. Because not everyone can be vaccinated – including very young babies, those who are seriously ill or have certain allergies – they depend on others being vaccinated to ensure they are also safe from vaccine-preventable diseases.
Vaccines protect against many different diseases, including:
- Cervical cancer
- Hepatitis B
- Japanese encephalitis
- Yellow fever
Some other vaccines are currently under development or being piloted, including those that protect against Ebola or malaria, but are not yet widely available globally.
Not all of these vaccinations may be needed in your country. Some may only be given prior to travel, in areas of risk, or to people in high-risk occupations. Talk to your healthcare worker to find out what vaccinations are needed for you and your family.
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:
• In phase I, the vaccine is given to a small number of volunteers to assess its safety, confirm it generates an immune response, and determine the right dosage.
• In phase II, the vaccine is usually given hundreds of volunteers, who are closely monitored for any side effects, to further assess its ability to generate an immune response. In this phase, data are also collected whenever possible on disease outcomes, but usually not in large enough numbers to have a clear picture of the effect of the vaccine on disease. Participants in this phase have the same characteristics (such as age and sex) as the people for whom the vaccine is intended. In this phase, some volunteers receive the vaccine and others do not, which allows comparisons to be made and conclusions drawn about the vaccine.
• In phase III, the vaccine is given to thousands of volunteers – some of whom receive the investigational vaccine, and some of whom do not, just like in phase II trials. Data from both groups is carefully compared to see if the vaccine is safe and effective against the disease it is designed to protect against.
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. More information about vaccine development and safety is available here.