Once a virus has entered the body, antiviral drugs can keep it in check.

Antivirals are used, among other things, to slow down the spread of HIV and cure hepatitis C. Now they can also be used to alleviate the symptoms of covid, which can be the difference between life and death for people at risk.

It is the immune system's reaction to the coronavirus that makes us sick.

Antivirals prevent the virus from spreading in the body so that the immune system is not overloaded.

Therefore, antivirals must be taken at an early stage of the disease when the spread is greatest.

- After the virus has multiplied, it is the immune system that is a problem, and that is what can kill people.

At that stage, the virus no longer multiplies, but it ensures that the immune system loses control over itself, and then no antiviral drugs help, says Anders Sönnerborg, professor of virology.

Concerns about side effects

One type of antiviral drug attacks the virus' copy so that the virus mutates to death.

There is a concern that the human genetic code could be damaged.

This type of antiviral drug is therefore not recommended for pregnant women or women of childbearing potential.

Men of childbearing potential are also advised to use condoms during intercourse as there is a fear that men's sperm may be affected and get genetic damage.

 - Even if it has not been proven, there is a concern that it can not only damage the virus' RNA but also human RNA.

These are theoretical considerations, they have not been described yet and hopefully it will never be relevant, says Anders Sönnerborg.

May develop resistance

The coronavirus can also become resistant to antiviral drugs by mutating, making the drugs less effective.

The virus has already developed resistance to the first version of antivirals that prevent the virus from entering the cell.

Medicines must therefore be constantly developed.

- These are first-generation antivirals, and there will be improvements in these in terms of efficiency and minor side effects and minor problems, says Anders Sönnerborg.

Play the video to see three different ways that antivirals prevent the virus from spreading in the body.

See more in The World of Science "How to stop the next pandemic" 20/3 in SVTplay and 21/3 at 20.00 in SVT2.