16th Jul, 2018

How Vaccines Work

As most of us are enjoying the seemingly endless days of sunshine the last thing we want to think about is another long, dark winter. But for those of you preparing for the upcoming seasonal influenza campaign you will be doing just that.

We know that efficient ‘flu clinics take a lot of preparation; in amidst ordering resources and preparing schedules you have to ensure that your knowledge is up to date and you feel competent with your injection techniques.

Naturally immunisation training has a practical focus, yet as you are administering medications it’s important you also have a general understanding of the principles surrounding vaccination (National Minimum Standards and Core Curriculum for Immunisation Training for Registered Healthcare Practitioners Revised February 2018).

The immune response 

Before we delve into what vaccines are and how they work, let's first look at our body's immune response, i.e. how it copes when faced with ‘pathogens’ such as bacteria or viruses.

When pathogens enter our body and begin multiplying and damaging other cells, infectious diseases can occur. Our bodies protect us from these diseases in various ways.  

We are born with certain innate immunity, e.g. a physical skin barrier to infection, whereas some immunity is acquired during our life.   

Acquired immunity is generally immunity to a single organism and can be passive or active.

Passive immunity

  • Protection is provided from an immune individual, e.g. to an unborn child via their mother’s placenta.
  • Usually provides short-term protection. 

Active immunity

  • Produced by your own immune system.
  • Usually long-lasting.
  • Can be acquired by exposure to a disease or by vaccination.

First exposure

When your body detects the presence of a pathogen it hasn’t seen before, it produces antibodies (specialised proteins produced by white blood cells, also referred to as ‘immunoglobulins’ and ‘gamma globulins’). These antibodies bind to the surface proteins present on the outside of the pathogen and form a vital part of your body’s immune response to fighting the infection.

It takes time for your immune system to manufacture enough of the correct antibody to fight the infection off. During this period the pathogen has time to grow, multiply and damage the body, causing you to experience symptoms of the disease.

Subsequent exposure

If your body's immune response is successful, it 'learns' how to make the right antibodies and will produce them more quickly if it detects the same pathogen again. This ongoing immunity is why, for example, most people are only ill with a disease such as chicken pox once. Even though you may re-encounter the virus, your body will fight it off before you notice any infection is present.

How vaccines work

  • Vaccination works by introducing your body to a pathogen (e.g. the ‘flu virus) so that your immune system can learn to produce the relevant antibodies and provide long-term protection.  
  • Following vaccination, if you come encounter that pathogen again your immune system should produce antibodies quickly enough to prevent any disease developing.
  • Therefore, vaccines can enhance your body's usual immune response without you being exposed to a previous infection.

[https://www.nhs.uk/conditions/vaccinations/how-vaccines-work/].

Types of vaccine

There are two types of vaccines: live and inactivated.

Live attenuated vaccines

  • Introduce a weakened form of the infectious agent to your body.
  • The agent reproduces, exposing you long enough to develop an immune response.
  • The vaccine is delivered in such a weak form it doesn’t make you ill with the disease.
  • The antibodies produced provide long-term protection. 
  • Examples include measles, mumps and rubella (‘MMR’). 

Inactivated (‘killed’) vaccines

  • Consist of intact bacteria, viruses or their extracts. 
  • Unable to reproduce so can’t cause the disease.
  • The antibodies produced may persist for months or years. Subsequent boosters may be required.
  • Examples include influenza and tetanus.   

Brief history

Though research is ongoing for new vaccines, the process of vaccination is far from new.

In fact, vaccination was discovered in the 18th Century by Edward Jenner, a British doctor. Jenner realised that people who had previously been infected with the unpleasant but generally harmless cowpox virus had immunity against the, usually fatal, disease smallpox.

Jenner tested his theory by deliberately infecting several of his child patients with cowpox then later exposing them to smallpox. Thankfully for his young patients, his hypothesis proved accurate.

The vaccine Jenner used was an early form of what today would be referred to as a 'live' vaccine.

Questions you may be asked

Due to the nature for the procedure, patients can be anxious when they attend for their immunisation appointment. If you vaccinate children, this anxiety extends to parents / grandparents etc! So, it can be helpful to prepare yourself for some of the questions you may be asked.

Are vaccines effective?

  • Yes.
  • Although different vaccines have different levels of effectiveness, all the vaccines licensed for use in the UK have been shown to provide a high level of protection against the diseases they are designed to counter.

Why should I get vaccinated / vaccinate my child?

  • Vaccination is the single most effective tool which exists in preventing outbreaks of infectious disease. Correctly used, vaccines save millions of lives around the world each and every year. (World Health Organisation)
  • On an individual level, following vaccination, you or your child won’t become ill if you ever encounter the pathogen concerned.

When a significant proportion of the general population has been vaccinated against a specific pathogen (e.g. smallpox), it becomes impossible for that pathogen to survive, since there are no people for it to infect where it can survive. This 'herd immunity' means that the whole community, including those who are unable to receive vaccinations for medical reasons, is protected. This is how the World Health Organisation was successfully able to eradicate smallpox worldwide through a concerted campaign of vaccination in the 20th Century.

Are vaccines safe?

  • Yes.
  • Any licensed vaccine has gone through rigorous stages of testing and trials before it is approved for use.
  • All medicines can have side effects, including vaccines. Most vaccine reactions are usually minor and short-lived, e.g. sore arm.
  • The risk of experiencing a severe side effect from a routine vaccination is rare and importantly, much lower than the risk of severe illness or death from the disease itself.
  • All healthcare staff delivering vaccination must undertake regular training.
  • There has never been any reputable scientific research linking vaccination to any adverse medical condition, including autism.
  • The 1998 study which raised concerns about a possible link between measles-mumps-rubella (MMR) vaccine and autism was later found to be seriously flawed and fraudulent. The paper was subsequently retracted by the journal that published it.
  • The MMR vaccine protects against Measles, Mumps, and Rubella which are dangerous - sometimes fatal - illnesses. MMR is one of the safest vaccines in the world [https://www.nhs.uk/conditions/vaccinations/mmr-side-effects/].

Spread the word!

Healthcare professionals have a major role in advising on and promoting the need for immunisation.

Herd immunity is lost, when the percentage of a population which has been vaccinated falls below a certain level.

The proportion required to be vaccinated differs across the range of pathogens, however, for measles a figure of 90-95% is often quoted. This is why it is vital that everyone who is medically able to receive vaccinations does so in accordance with the recommended schedule.

  • Further information about vaccinations, the UK immunisation schedule and relevant vaccines is found in the ‘Green Book.’


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Post last updated on 16/07/2018