This week, Pfizer announced that it has launched a scientific study to test a preventive pill against covid-19, writes Reuters.

The American pharmaceutical giant is far from alone in trying to develop drugs against the virus.

Competitors MSD and Roche Holding AG are also underway, according to the news agency.

Many of the pills that are developed and tested are antiviral drugs.

Vaccine researcher and professor Matti Sällberg explains:

- It attacks the virus directly by affecting its various proteins or enzymes - and blocks it.

It is a drug that can hopefully stop the virus from multiplying.

Therefore, it is very important to give it as early as possible during a viral infection.

Given with HIV medicine

In Pfizer's study, 2660 people over the age of 18, living in a household with a covid-infected, will take the pill along with a low dose of the HIV medicine Ritonavir.

- You can call it (Ritonavir) a booster - it prolongs the half-life of the drug and then you do not need to take the same high dose as often.

You get a slower breakdown of the drug, says Matti Sällberg.

Pfizer has also started another study among adults with covid-19 symptoms.

The pharmaceutical company's MSD's study - which is being carried out in Sweden, among other places - is testing an antiviral drug on unvaccinated people in the risk group.

Although the 3-study is expected to be completed this autumn.

- Then you have reached as many patients as you need to draw conclusions, says Magnus Gisslen, principal investigator for the study in Sweden.

Unclear about side effects

The goal is 1850 patients, according to Magnus Gisslen - who on a daily basis is a professor at Sahlgrenska Academy and chief physician at the infection clinic at Sahlgrenska University Hospital.

He follows much of the research on corona pills.

- The studies done so far are not large enough to provide reliable information about side effects - more individuals are needed in the studies.

No pill against covid-19 has yet been approved for use in Sweden, how the studies are going remains to be seen - but Matti Sällberg is hopeful.

- Hopefully Pfizer's pills will come, with a little luck it will give good results.

We can see quite simply, but there is a lot going on.

What makes a corona pill different from a vaccine?

Hear Matti Sällberg answer in the clip above.