Why are viruses so difficult to prevent? - coronavirus explained.

When someone is infected with a virus there is very little that common drugs or medicines can do to attack the pathogen directly. Doctors can try treatments such as bringing down the fever, keeping the patient hydrated, and helping them breathe through ventilators but, ultimately, the human immune system is on its own.

The reason for this is that viruses mostly reside inside our cells because that’s where they replicate. Therefore, viruses are very difficult for our immune system and drugs to attack since these exist outside of cells. It’s like the viruses are trying to hide from the police (our immune system cells/drugs) which are patrolling the streets so, the logical solution is to go inside buildings (host cells) where it's less likely they will be found.

Retroviruses (like coronavirus, ebola and HIV) enter human cells, convert their RNA genome into DNA and incorporate it into the host’s DNA. Therefore, every time the host cell replicates its DNA it also replicates the DNA of the virus from which new complete viral units (virions) can be made.

Within the infected cell the viral DNA is used to create viral proteins which are used to package the virus' genome into virions by hijacking the host cell. The virus' population will grow and grow as the host cell replicates until eventually the cell bursts, releasing hundreds of virions into the host’s body which will go on to infect more cells.

Therefore, the most effective way viruses can be targeted is by preventing them from replicating; if they can’t reproduce and infect more cells eventually the virus will die out and the host will start recovering. However, to do this we will need to target our own replication machinery, meaning our cells will also not be able to multiply so will die.

Obviously, the last thing we want to do is kill our own cells because that would have drastic consequences. Therefore, we need to target a feature of the virus that is unique and that isn’t similar to the host human cell. However, finding a unique feature is extremely difficult as all are very similar to that of their hosts since the virions are technically made by and using parts of their host cell.

It’s like finding a needle in a haystack. The only way to identify this feature is to trawl through the entire virus (taking hours and hours of research and lots of money) and even then there’s only a tiny chance you’re actually going to find it.

To make matters even more difficult, viruses are incredibly diverse so even if we do eventually find a way to kill one it probably only works for that specific virus. This is because viruses are like food; there are so many types all of which are made of different ingredients and made in different ways, if we poison one ingredient most foods are unaffected.

This is also part of the reason why the human immune system struggles to fight viruses. They’re all so unique meaning the body has to start from scratch when trying to fight one because it probably hasn’t seen anything like it before so it doesn’t know how to / isn’t equipped to attack it.

This is where vaccines come in.

When given a vaccine you can be given the virus but this form of the virus is very weak so the effect that it has on your body won’t be very severe. The idea behind this is that your immune system has a chance to practise as the body will react to the virus in the same way it would if it was infected by the real thing, but since it’s weak it won’t cause illness.

Or, a vaccine could instead contain the specific antibodies that will target the particular virus. This means if you do catch it you already have the correct antibodies present to attack so the virus will be quickly defeated and you won’t experience many symptoms.

It’s like fighting a real-life war. If a conflict suddenly breaks out of nowhere no one is prepared; there are no weapons or any soldiers so chances are you probably won’t win the fight, or at very least you’ll end up severely wounded. However, if you’ve already practised fighting this particular enemy or if you already have the correct weapons and soldiers on standby you’re ready to fight and know what to expect. Now if the conflict was to break out the tables have turned and you can easily defeat the opposition without suffering from too many injuries.

So, if a vaccine is the way to stop viruses like coronavirus and thousands of top scientists have been working on vaccines for months already, why don’t we have one?

Well, apart from the huge cost, to find or create antibodies or a modified version of the virus is extremely difficult and you can never really be sure it is actually weak. For example, every person is different in that although everyone’s DNA is generally the same the molecules that affect how the DNA and genes are expressed varies (epigenetics). This means when infected by a virus that hijacks your cells, the rate that it replicates and the effect that it has on the body varies.

This helps to explain why viruses have different effects on different people, such as being deadly to one person but for another it has no effect even though it’s exactly the same virus (they’re asymptomatic). Therefore, it makes sense that a version of a virus used in a vaccine may have little effect on most people but on some it may well still have catastrophic effects.

This might be what happened in the coronavirus vaccine trials by the University of Oxford and AstraZeneca this week.

Their vaccine contains a chimpanzee cold virus which is unable to replicate so won't make the host ill and it also delivers the gene for the coronavirus spike protein. This protein helps coronavirus attach to human cells so that it can then infect them. Therefore, if our body can recognise this protein and neutralise it using antibodies the virus can't spread to more of our cells and we won't become ill.

For most of the volunteers the vaccine works; it triggers an immune response so the body generates the right antibodies ready to use if the real virus comes and the person doesn’t suffer from many side effects. However, for one volunteer the vaccine maybe didn’t quite go to plan and they became very ill - the version of the cold virus they used may not actually be weak.

This is why vaccines must go through such long vigorous trials before being made available to the public. Scientists paused the trial and investigated whether the inflammatory syndrome that the volunteer was diagnosed with was in fact caused by the vaccine or whether it was caused by something else.

The university has since said it is deemed safe to continue so trials have been resumed, suggesting the severe illness was not caused by the vaccine. We should all remain hopeful that an effective, safe vaccine can be found and that it can be given to members of the public relatively soon.

We will put an end to coronavirus.

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Avril, T., (2020). Why The Coronavirus And Most Other Viruses Have No Cure. Medicalxpress.com.

BBC News. (2020). Coronavirus: Oxford University Vaccine Trial Paused After Participant Falls Ill. BBC.

Le Page, M., (2020). Everything You Need To Know About The Oxford Coronavirus Vaccine. New Scientist.

**Image by CDC on Unsplash**