Thread by @apsmunro

I've spent the last year running #COVID19 vaccine trials, and am leading one now as part of my PhD

I've spoken to A LOT of people about these vaccines!

If you ever feel confused about the vaccines against #COVID19 , hopefully this is the thread for you

We'll keep it simple!💉

Vaccines work by using your adaptive immune system (the part which remembers bugs) which is made up of 2 major parts:

- Humoral: Cells make antibodies to tag/attack bugs
- Cellular: Cells which directly recognise and attack/kill bugs (mainly T cells)

Usually, your immune system would see a bug (often a virus or bacteria) and learns how to recognise it by remembering specific bits we call "antigens"

It makes lots of antibodies and cells against these antigens the first time it sees them, ready to fight next time they appear!

Here's why vaccines are clever

They shows your immune system these antigens before you ever see the real bug, so your body has already prepared to fight it BEFORE the bug had a chance to make you sick!

So why do we normally give 2 doses of vaccine?

Your body treats the first exposure a bit like a warning shot, then second time gets serious about it by a process called "affinity maturation"

Amazing thread here by @andrew_croxford for more details

https://twitter.com/andrew_croxford/status/1399477303357411338?s=20

Loads of vaccines for COVID-19 have either been approved for emergency use, or are likely to be in the near future

They are all ingenious ways of delivering antigens to your immune system to help it learn to fight the SARS-CoV-2 virus before it's ever met it!

Lets look at some

The new kids on the block are the mRNA vaccines

These include the Pfizer/BioNTech and Moderna vaccines which have been approved, and Curevac which is currently in phase 3

We've never had mRNA vaccines for anything before! How do they work?

Your body usually uses its own mRNA to translate the coding of your DNA into proteins in your cells

mRNA lasts a very short time then disappears - poof 🌬️

The mRNA vaccines contain mRNA coding for an antigen from the SARS-CoV-2 virus - the Spike (or S) protein

Your muscle cells use this mRNA to make the S protein yourself, which your immune system then generates antibodies and immune cells against!

Then - poof! It disappears!

The other major vaccines in use currently are Adenovirus vector vaccines

These include the Oxford/AstraZeneca vaccine, and the Janssen/Johnson & Johnson vaccine

These vaccines use another virus which has been rendered completely harmless materials for the antigen

Ox/AZ uses a chimpanzee Adenovirus
Janssen uses a human Adenovirus

Neither can replicate/grow or cause infection, they are harmless!

These viruses however carry the DNA for the S antigen from the SARS-CoV-2 virus

Your body uses this DNA to make the S protein, which your immune system then makes antibodies and cells to fight against

Another vaccine which might be approved soon is Novavax!

This vaccine uses a more traditional method of delivering the antigen - it just contains the antigen!

OK it's slightly more complicated than that...

The Novavax vaccine contains a purified S protein alongside an "adjuvant" called Matrix M

Adjuvants are just what we call materials which help stimulate a more potent immune response, as sometimes the antigen by itself with no virus makes the immune system just go, "meh..."

Another different kind of vaccine in use using more traditional technology are "whole virion" vaccines

Instead of just the S protein antigen, these deliver the whole SARS-CoV-2 virus (don't worry, they kill it first!)

These include Sinovac/Coronavac, Sinopharm, and Valneva

Valneva is a little bit different though

It also contains an adjuvant, called CpG1018

This helps it stimulate a much stronger immune response, which overcomes some of the seemingly reduced efficacy of other whole virion vaccines compared to mRNA/vector vaccines

So how effective are these vaccines?

They are unbelievably good - in fact, they have blown away all our expectations

Both in clinical trial AND real world observational data, they provide exceptional protection against severe disease (and probably from all current variants)

Initially there was some uncertainty about how much they would reduce transmission, but now there is good real world evidence that they reduce both:

- Your chances of becoming infected
- Your chances of infecting someone else if you do get infected

This is one of the main reasons why vaccines are so incredible

By getting vaccinated, not only do you protect yourself

You protect all the people around you

Everyone wins

How safe are the vaccines?

They are very, very safe indeed. There are fewer medications you could take which are safer.

They do have side effects, which are mainly feeling lousy and flu like for 24 - 48hrs, and that's pretty common.

What about more serious stuff?

We know now that the adenovirus vector vaccines are associated with an increased risk of clotting, alongside low clotting cells

These clots can be very serious, but the risk is extremely low, particularly for older people

The clots are also a lot more common if you catch COVID

Although the risk is very, very low, if your risk of actually catching COVID-19 is very low, and your risk of getting very sick if you catch it is very low (e.g. young people), some countries are recommending you have a different vaccine as first choice

The mRNA vaccines are also very safe, but do come with an slight increased risk of anaphylaxis (severe allergic reaction, which can be treated), or in young men possible increased rates of inflammation of the heart (myocarditis) - although this seems mild and temporary

That's all for now!

I hope that was useful - if you want more info about #COVID19 vaccines, or just vaccines in general I highly recommend the @OxfordVacGroup knowledge project website

vk.ovg.ox.ac.uk/vk/

#VaccinesWork 💉