Everything you need to know about anti-Covid pills

US pharma giants Merck and Pfizer have announced encouraging results for oral drugs in what could open up a new chapter in the fight against the pandemic.

They are pills taken orally as soon as the first symptoms of Covid-19 appear, to avoid serious forms of the illness, and therefore hospitalisation.

This form of treatment has been sought since the start of the global health crisis.

After months of research, Merck and Pfizer say they have reached that elusive goal.

Early October, Merck said it was seeking authorisation in the United States for its pill molnupiravir, and Pfizer followed suit on Friday with paxlovid.

They are both anti-virals that act by reducing the virus's ability to replicate, slowing down the disease.

Both companies say clinical trials showed a strong reduction in the risk of hospitalisation.

Those who took molnupiravir saw that risk diminish by 50 percent and those who took paxlovid by nearly 90 percent, although direct comparisons of these efficacy rates should be avoided because of the different study protocols.

Why is this a big deal?

If the efficacy of these drugs is confirmed, it will be a major step forward in the fight against Covid-19.

They would add to vaccines to bolster the world's therapeutic arsenal against the virus.

A pill can be quickly prescribed to a patient who will then take it easy at home compared to the drugs which are injected and therefore more difficult to administer.

"The success of these antivirals potentially marks a new era in our ability to prevent the severe consequences of SARS-CoV2 infection," British virologist Stephen Griffin told the Science Media Center.

How much will it cost? 

Merck's molnupiravir has already been approved in the United Kingdom where health authorities on Thursday gave their green light to its use in patients at risk of developing a serious form of the illness, such as the elderly, obese people, or those suffering from diabetes.

READ MORE: UK becomes first country to authorise anti-Covid pill

US and EU health authorities are also urgently reviewing the drug.

The European Medicines Agency promised on Thursday to "accelerate" proceedings, without giving a firm date.

Several countries have already ordered stocks of molnupiravir, such as the United States, with 1.7 million courses of the drug.

The US order gives an idea of the steep price of the drug.

READ MORE: US signs $1.2M deal to procure 1.7 million courses of Merck's Covid-19 pill

It comes to $1.2 billion, which equates to around $700 for a five-day course.

As for Pfizer, while it has not outlined a price for paxlovid, it has promised it will be "affordable" and subject to a tiered pricing approach based on the income level of countries.

Pfizer and Merck have said they are making efforts to expand global access to the drugs. Pfizer said it expects to produce more than 180,000 courses of its therapy by the end of this year, with production of at least 50 million planned for 2022. Merck has said it expects to produce 10 million courses of its drug by the end of this year, with at least 20 million set to be manufactured in 2022.

How does it work?

Both drugs are given for five days. Pfizer's regimen is three pills in the morning and three pills at night. Merck's drug is taken as four pills in the morning and four at night.

Pfizer's drug is part of a class known as protease inhibitors designed to block an enzyme that the coronavirus needs to multiply.

Pfizer said that because the drug targets a part of the virus essential to replication, the pathogen cannot become resistant to the treatment.

Pfizer's drug is given in combination with ritonavir, an older antiviral that boosts the activity of protease inhibitors but can cause gastrointestinal side effects and interfere with other medications.

Merck's pill, developed with Ridgeback Biotherapeutics, is a nucleoside analogue with a mechanism of action that aims to introduce errors into the genetic code of the virus.

Because the drug generates random mutations into the virus, it is difficult for the coronavirus to evolve and become resistant.

What does the data say?

It is difficult so far to properly evaluate Merck and Pfizer's treatments given both groups have only published statements and have not made the data of their clinical trials available.

French infectious diseases specialist Karine Lacombe warned in September that these types of announcements should be treated with "caution" until the studies can be scrutinised.

She pointed out that these treatments represent a "potentially enormous" market for pharmaceutical groups.

Nevertheless, some elements indicate that Merck and Pfizer are not making empty promises.

For one, they both stopped their clinical trials earlier than expected as the results were so strong, with the okay of independent monitoring committees.

Where fluvoxamine is concerned, the data is available but is not without criticism.

Several researchers have complained that the authors did not just limit themselves to evaluating the frequency of hospitalisations, but also assessed the frequency of prolonged emergency room stays.

This, they say, complicated the interpretation of data.