How do vaccines work?

January 2020

Vaccines are one of the most effective public health interventions in history, saving billions of lives since the first vaccine was produced in 1798. The World Health Organization (WHO) estimates that vaccines prevented at least 10 million deaths in just five years between 2010 and 2015 alone. So how exactly do they work?

At any time, there are trillions of bacteria and viruses on or inside the human body – not all of which can cause disease. When disease causing bugs (such as, bacteria, viruses, fungi or parasites, for example) do get into the body, however, our immune system recognises them as “intruders” and works to protect us by producing antibodies.  Antibodies stick to and kill or disable the harmful bug.  This process takes time, as your body tries to produce the right antibody for the intruder, during which you may become very unwell – even die.

However, once your body has developed successful antibodies, they remain in the bloodstream. This means that if particular bug returns, your body can react immediately to fight it. Vaccines are based on this natural defense mechanism to help protect us against some of the world’s deadliest diseases.

Vaccines work by introducing small, harmless amounts or fragments of the bugs which cause disease, which are dead, weakened or inactive, into your system. This “tricks” your immune system into developing protective antibodies. Then, if the “real” version of that intruder ever gets in, your body already has the antibodies it needs to neutralise it – often before you even notice.

Vaccines are available to protect against many diseases, including:

  • Cervical cancer
  • Cholera
  • Hepatitis B
  • Influenza
  • Measles
  • Meningitis
  • Mumps
  • Pneumonia
  • Polio
  • Rabies
  • Rotavirus
  • Rubella
  • Tetanus
  • Yellow fever
Is this process safe?

Yes. Vaccines are thoroughly tested and are the safest way to develop protection against some common causes of deadly disease. As with all drugs, vaccines can cause side effects such as soreness/redness at the injection site in some people, but any vaccine that is given to a child or adult is rigorously tested and monitored for safety, to ensure that the benefits outweigh any risk.

The overwhelming evidence shows that vaccinating is safer than not vaccinating.



If you have questions or concerns about vaccines, our support team can help.
Why don’t some people get vaccinated?

Despite their safety and their success, some people don’t always get the vaccines that are available to them. Often this is due to the inconvenience of accessing the vaccine, but it can also be due to lack of awareness of the disease (because vaccines have reduced the disease to such low levels it is rarely seen), or misunderstanding the safety of vaccines. . In fact, the World Health Organization (WHO) has listed vaccine hesitancy as one of the top ten threats to global health in 2019.

Click here to find out why this is the case.

If they’re so effective, why aren’t they mandatory?

Mandatory vaccination is something that’s long been debated, and remains under debate today.

Click here to read our view

Can vaccines protect against meningitis?

There are safe and effective vaccines available that that protect against the most common causes of life-threatening bacterial meningitis and septicaemia (meningococcal, pneumococcal and Hib). These are routinely available in many different parts of the world and have saved millions of lives.

However, not all causes of meningitis and septicaemia are vaccine preventable, which is why it’s always important to remain aware of the signs and symptoms – even if you have had all your available vaccines.

Meningitis Research Foundation encourages everyone to take up the vaccines that are available to them, and continues to campaign for greater vaccine access throughout the world.

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Since the charity was founded in 1989, we have awarded 161 research grants. The total value of our investment in vital scientific research is over £19.1 million (€24.7 million).
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About the author

Holly Edwards
Senior Communications Officer

Hi, I'm Holly, and I joined MRF in 2017.

I'm always looking for stories that will help more people understand meningitis and the devastating impact it can have. Working with people who have been affected by meningitis is a great privilege, and I feel very lucky to do what I do.

Tel: 0333 405 6255