So as per @sindivanzyl’s request, this is a continuation from yesterday’s thread on our immune systems.

This will focus on vaccines, and how they work. We’ll look at how Covid19 vaccines fit in as well.

/1

So we discussed yesterday how the ‘adaptive’ arm of the immune system has the ability to ‘remember’ previous pathogens . It does this via ‘memory’ B and T cells.

Vaccines exploit this.

But HOW? /2

The immune system identifies ‘antigens’ (molecules on the outside of pathogens) that it targets.

Pathogens can have multiple ‘antigens’ for the body to focus on. /3

So vaccines work by exposing the immune system to these antigens.

In turn, the body makes antibodies against the antigens to fight them.

This can be done in a number of ways. /4

The first is with ‘live vaccines’ where we expose the body to a weakened (or ‘attenuated’) form of the pathogen.

We weaken the pathogen in the lab then inject it into the host.

Examples include: Oral polio vaccine, BCG, Measles/Mumps/Rubella (MMR)/ Rotavirus/Yellow Fever etc /5

Pros: Live vaccines usually provoke an excellent, often life-long response (i.e. you don’t often need boosters).

Cons:
- Rarely, especially in those with weak immune systems, the vaccine can cause the disease its vaccinating against!
- Not for pregnant women /6

Other options are:
- kill the pathogen (inactivated polio, hepatitis A, flu shot) and inject it
- expose the host to just its toxin (tetanus, diphtheria)
- or simply expose the immune system to PART of the pathogen

The last group are called ‘fractional’ vaccines. /7

Fractional vaccines are cool because they obviously can’t cause disease (there’s no actual pathogen).

The down side is they sometimes have to be attached to things to provoke a response. And they often need boosters. /8

There are lots of fractional vaccines. - Some are bound to sugars (or ‘polysaccharides)
- some target a particular subunit of a pathogen
- some are ‘conjugated’ with a toxin to boost immune response.

Examples: PCV, Meningococcal, pertussis, Hib, Hep B /9

There are now 5 (and counting!) Covid vaccines and they make use of some of the above, while implementing new(ish) technology.

The first are the mRNA vaccines.

Scientists decided the best antigen to target was the ‘spike protein’ /10

The spike protein is how the virus gets into the cell.

So scientists came up with a way to get the cell to make this spike protein.

They inserted the instructions (or messenger RNA - mRNA) into fatty ‘bubbles’. These ‘bubbles’ allow the mRNA to ‘float’ into cells. /11

The mRNA instructions are for the spike protein ONLY, and not the rest of the virus. Imagine the recipe for the icing of a cake. But ONLY the icing.

The cell reads these instructions and makes the spike protein which then leave the cell. /12

The innate immune system sees these proteins, presents them to the adaptive system, B cells kick into gear and make antibodies...

And voila! Next time your body sees the REAL Covid19, antibodies and B cells are primed and ready. They attack the spike protein and kill Covid! /13

The other Covid vaccines are similar. The AstraZeneca, Sputnik and J&J ones contains the actual DNA which is buried into adenovirus (either chimp or weakened human- so not harmful)

This enters the cell, the DNA tells the cell to make the spike protein. Same effect. /14

There are some inactivated vaccines in the mix (Sinopharm), and a WHOLE bunch of others on the way.

We’re likely to have a big selection by the middle of next year. Some will obviously work better than others /15

So this is the basics of vaccines and the Covid vaccines! I hope this was helpful and not too confusing (if you made it this far congrats! Vaccines are simple but complicated!)

Tomorrow, I’ll talk about some side effects and who should not take these vaccines. /end