As vaccine delivery is rolled out, the major worry globally is whether this action will protect against the new variants of the virus. Yesterday media worldwide reported on a third new variant, emerging from Brazil, similar genetically to those from South Africa and the UK. The most recent data suggest that current vaccines are probably still going to work but we are right to remain cautious. The aim of this post is to explain in simple terms how these variants could reduce the success of the virus.
Let’s start with the virus
- Apologies for repeating what most of you will know, but it is the spikey bits on the surface of the virus that are most important in terms of its ability to cause infection
- These spikes have at their tip a bit of the protein that allows the virus to attach itself to human cells. I call it the ‘key bit’ in that picture (the posh word is “receptor binding domain” or RBD), ie it is like a key that needs to find the right lock
- Thus, when the virus has multiplied it can only attach to human cells, for example in the nose or throat, when it finds a lock it can fit
- The posh word for that perfect lock is called a ‘receptor”
So how do the vaccines directed against the spike protein work?
- In simple terms Covid-19 vaccines aim to stop the spike protein attaching to cells by preventing that ‘lock and key’ process
- Vaccines work by producing antibodies (as I am sure you all know by now!) that stick to the spike protein of the virus, thereby stopping it attaching to the receptors
- In the picture below, antibodies are shown as Y shaped chemicals that have locked onto the spikes, thus preventing the virus locking onto the surface of cells
How does this relate to the new variants?
- The spike protein is a very complex shape indeed (see picture below!)
- The antibodies produced by all the vaccines all recognise the main aspects of the shape of the spike protein
- The virus mutates all the time and thus the exact shape of the spike protein will vary between different mutations*
- Thus the spike protein that the vaccines are designed to produce may be different from the spike protein of a new variant of the virus that we are exposed to
- Fortunately, most mutations do not sufficiently affect the shape of the spike protein to interfere with the success of the antibodies
- The particular problem with the new variants (which was not the case with other mutations) is that these mutations do affect the shape of the key bit (RBD) of the spike protein
- Thus, the concern is that antibodies produced against the spike protein in the vaccine will not lock onto the spike proteins on the new variants of virus, so the virus will be free to lock onto the human cells and cause a clinical infection
*I did show in an earlier post how mutations can change the shape of a protein which if you are interested you could have look at:https://makingsenseofcovid19withs.com/2020/12/08/is-this-the-greatest-breakthrough-in-medical-science-for-a-generation/
What do we know so far?
- As mentioned above this is such an active, even frenzied, area of research, my comments may be out of date even as I publish this post (I will try and keep abreast!)
- Some things do seem clear:
- It seems that the antibodies produced by the vaccines may have reduced potency against the new variants, but will not be completely rendered ineffective so
- Pfizer have however carried out new laboratory tests of their vaccine with the UK variant and found that the antibodies produced were successful in neutralising this variant – that is what we needed to know
- The theoretical likelihood of new variants being a problem for the vaccines is also greater with the Brazilian and South African variants than with the UK one
- The reason is a complex one: the UK variant does not have exactly the same mutations in the key part of its spike protein and so the antibodies from the existing vaccines should still be effective (ie supporting the results of the Pfizer study above)
What about immunity to natural infection?
- I only covered this 2 days ago, before some of these new data appeared!
- My take at present is that although the same concerns apply – “if I have been infected will I also be protected against the new variant?” – my guess is that natural immunity should be more resilient than vaccines to changes in the virus because:
- Vaccines produce an immune response just to the (albeit very important) spike protein
- Whereas natural infection (as I said in this week’s post) produce an immune response to many different parts of the virus
- What is disturbing about the news yesterday of the spread of the new variant in Manaus, is that this region of Brazil had already been devastated by Covid-19 and it was hoped that the population had reached herd immunity
- I don’t think this proves that natural immunity did not work in the 60% of the population that had been infected, but rather that with the new variant herd immunity is going to be that much harder to achieve
- Take home message from all this – we ALL need to be vaccinated
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