How do viruses develop resistance against vaccination?

A recent study shows that two SARS-CoV-2 variants are resistant to new COVID-19 vaccine. But how do viruses develop this resistance?

This article discusses the way that viruses mutate to evade vaccines and the immune system.

Recent study shows SARS-CoV-2 variants are resistant to vaccination

A recent study has discovered that the U.K. and South African variants of SARS-CoV-2 (B1.351 and B1.1.7) are resistant to the recently rolled-out vaccines. This raises the hair-raising question of whether the virus will inevitably evade our efforts at vaccination by constantly mutating at a rate too fast to keep up with. 

In line with this, one of the companies developing a vaccine, Novavax, reported that while their vaccine was around 90% effective in the U.K., it was only 49.4% effective in South Africa (where the variant present is primarily B.1.351).

The fear is that, similar to the influenza vaccine, we will constantly be on the back foot trying to prevent the spread of COVID-19 as the virus mutates to evade our efforts.

How does the immune system fend of viruses?

The body is very good at recognizing foreign objects – sometimes too good. When something foreign enters the body, like a virus, it very quickly reacts and begins trying to remove it. In the case of viruses, one way it does this is by producing antibodies.

Antibodies are proteins that can recognise and “stick” to the virus. They do this by recognising a part of that virus known as an antigen – usually a small protein on the external face of the virus.

The way an antibody binds to an antigen is similar to Velcro – it’s very specific and usually only one antibody will bind to a particular antigen. 

Once the antibody binds to the foreign body it acts like a marker signalling your immune system to destroy it.

Usually, this also means that after the infection is fought off you are immune to that pathogen.

Vaccines work in a similar way, usually by provoking the production of antibodies with inert viral proteins which cannot cause an infection. Then, if the actual virus enters your body, it already has the correct antibody stored in a sort of memory which can be quickly employed to prevent infection. 

How does a virus mutate to evade vaccines and treatment?

Viruses constantly mutate. This does not always cause problems for virulence or treatment – but it can. There are many different kinds of virus, but to explain this phenomenon I will use the example of RNA viruses – such as Influenza and SARS-CoV-2.

Firstly, it is important to understand the structure of an RNA virus and how they replicate. The viruses have a genome which is the totality of their genetic code. This code is used to produce a protein “shell” which encases the genome.

A mutation is a change in the genome of a virus. Such a change may result in changing the structure of the virus itself (by changing its protein makeup). If this part of the virus is what the immune system uses to recognise or combat it (the antigen), then the virus may become more aggressive or harder to treat. This is known as antigenic drift.

If the virus mutates, however, it is similar to changing the lock in your door – the key no longer fits.

How viruses mutate is quite interesting. They actually have defective machinery – a protein called RNA polymerase which is involved in replicating the virus. This protein places each part of the genetic code in a row as a new virus is being formed, but it is prone to errors. This means that each new copy of the virus may be more or less virulent. The more virulent strains are more likely to survive and spread between people – this is how a virus evolves to avoid our immune system.

What does this mean for the future of COVID-19?

The outcome depends on how quickly the virus mutates. In the case of Influenza there is a lag time between the identification of a new strain and the production of a vaccine which means we are always behind the curve in preventing new outbreaks. 

We are already seeing that new variants of SARS-CoV-2 can effectively evade our cutting-edge vaccines. The good news is that SARS-CoV-2 appears to mutate at a much slower rate than Influenza.

As the vaccines are rolled out we are likely to see a drop in the spread of the virus – which means that we are preventing it from replicating. If the virus cannot replicate effectively, then it cannot mutate into more dangerous forms.

It may be important to identify the more virulent strains of SARS-CoV-2 and target those regions with the preventative measures we have seen be effective so far – social distancing, masks, and hopefully effective vaccines.

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