US pharmaceutical giant Pfizer on Tuesday announced a deal to make its oral antiviral Covid-19 medication available more cheaply in poorer countries, if the promising pill passes trials and regulatory approval.

Pfizer, which also produces a Covid vaccine with German lab BioNTech, said it had signed an agreement to sub-licence production of its Paxlovid pill to generic drug manufacturers, without receiving royalties.

The deal with the global Medicines Patent Pool (MPP) would therefore make the candidate drug available at a lower cost in 95 low- and middle-income countries covering around 53 percent of the world's population.

It follows a similar deal for US rival Merck & Co last month.

The drug is to be taken with the HIV medicine ritonavir.

Interim data from ongoing trials demonstrated an 89 percent reduction in the risk of Covid-19-related hospitalisation or death compared to a placebo, in non-hospitalised high-risk adults with Covid-19 within three days of symptom onset, said Pfizer.

Similar results were seen within five days of symptom onset, it added.

The Geneva-based MPP is a United Nations-backed international organisation that works to facilitate the development of medicines for low- and middle-income nations.

MPP executive director Charles Gore said: "This license is so important because if authorised or approved, this oral drug is particularly well-suited for low- and middle-income countries and could play a critical role in saving lives."

The drug "is to be taken together with ritonavir, an HIV medicine we know well, as we have had a license on it for many years, and we will be working with generic companies to ensure there is enough supply for both Covid-19 and HIV."

HIV drug mix 

Pfizer will forego royalties on sales in all countries covered by the agreement while Covid-19 remains classified as a Public Health Emergency of International Concern by the World Health Organization.

Last month, the WHO maintained the highest level of alert over the spread of the SARS-CoV-2 virus that causes Covid-19.

Paxlovid, or PF-07321332, is an investigational antiviral therapy designed to block the activity of the SARS-CoV-2-3CL protease -- an enzyme that the coronavirus needs to replicate.

Taking it together with a low dose of ritonavir helps slow the breakdown of PF-07321332. It therefore remains active in the body for a longer period at a high concentration, to help combat the virus.

If taken at the first sign of infection or exposure to Covid-19, the pill could potentially help patients avoid severe illness, which can lead to hospitalisation and death, Pfizer said.

"We believe oral antiviral treatments can play a vital role in reducing the severity of Covid-19 infections, decreasing the strain on our healthcare systems and saving lives," said Pfizer chairman and chief executive Albert Bourla.

"We must work to ensure that all people -- regardless of where they live or their circumstances -- have access to these breakthroughs."

While the search for vaccines has resulted in multiple products being approved for emergency use in the pandemic, the hunt for treatments for those who have already caught the disease has not been as fruitful.

Agreement follows Merck deal 

The MPP was founded by Unitaid, which works on innovations to prevent, diagnose and treat major diseases in poorer countries.

"During a pandemic, saving time means saving lives. This agreement could help us to reach more people more quickly as soon as the medicine is approved and, when coupled with increased access to testing, bring benefits to millions," said Unitaid executive director Philippe Duneton.

Potential sublicensees have until December 6 to register an expression of interest.

The announcement comes after the MPP last month signed a similar deal with Merck.

That voluntary licensing agreement would facilitate affordable worldwide access for its investigational oral antiviral medicine molnupiravir.

Subject to regulatory approval, the deal will help create broad access to molnupiravir in 105 low- and middle-income countries.