Vaccines do something very clever. 🤓

They take advantage of the immune system’s ability to remember previous infections and develop what we call ‘protective immunity’ — a protection against getting the same infection again.

Essentially, vaccines aim to induce an immune response against a pathogen that is very similar or often even better than the immune response during the infection itself.

This can be a full protection, meaning in most cases you don’t get sick at all when you catch the infection. Or it can be a partial protection, meaning you don’t get as sick as someone without the vaccine.

In order to do that, there are two main options:

1. Often you receive a safe and harmless (‘attenuated’) live version of the original pathogen, which still causes a mild infection (and which in many cases you won’t even notice).

2. Other vaccines just contain bits and pieces from the pathogen, which won’t cause a live infection but the immune system will still mount a protective immune response against them. This can use mashed-up inactivated bacteria or viruses, purified components such as viral proteins, or a molecule called mRNA.

In most vaccines, the protection against infection is achieved by the production of specific antibodies against the pathogen and the generation of memory T-cells and B-cells. This memory can persist for many years, sometimes even for life! In other cases, your immune system may need a ‘booster’ as a reminder of what the pathogen looks like.

A bit like you having to revise before a school exam.

8 December 2020: 90-year old Maggie Keenan from Coventry is the first person in the world to receive the newly approved Covid-19 vaccine.