Pfizer Inc. said on Tuesday it has agreed to sell up to four million courses of its oral COVID-19 antiviral treatment Paxlovid to UNICEF for use in 95 low-income countries.

The deal accounts just over three per cent of Pfizer's projected production of 120 million Paxlovid courses for this year. The company said the 95 countries covered in the UNICEF deal account for around 53 per cent of the world's population.

Pfizer Chief Executive Albert Bourla said in a statement that the deal with the United Nations Children's Fund was an important part of the company's strategy to work toward equitable access to the pill for all, "regardless of where they live or their circumstances."

The drugmaker did not disclose financial terms of the deal, but said that low- and lower-middle-income countries will be offered the drug at a not-for-profit price, while upper-middle-income countries will pay more.

Pfizer expects to be able to fulfill some of Paxlovid orders for these countries in April, and said supply will continue through the year.

Paxlovid is expected to be an important tool in the fight against COVID-19 after it reduced hospitalizations in high-risk patients by around 90 per cent in a clinical trial. The results were significantly better than those for Merck & Co's rival antiviral pill molnupiravir in its clinical trial.

Paxlovid is a two-drug treatment that pairs a new compound, nirmatrelvir, with the older antiviral ritonavir. Both are pills meant to be taken for five days beginning shortly after COVID-19 symptoms occur.

Pfizer has already struck a deal with the UN-backed Medicines Patent Pool (MPP) to allow more than 30 generic drugmakers to manufacture cheaper versions of the drug to sell in the 95 countries, but none are expected to be available before early 2023.

Last month, Pfizer said it expected Paxlovid sales of at least US$22 billion in 2022. Bourla noted that actual sales could be much higher by year end, noting that the forecast was based on contracts for only a fraction of the company's total expected production of Paxlovid.

Pfizer has struck deals to sell the pills to a number of countries already, including 20 million courses to the United States this year.

Beyond the UNICEF agreement, a Pfizer spokesperson said the company is also in talks with the World Health Organization and the Access to COVID-19 Tools Accelerator (ACT-A), an effort by governments and NGOs to procure tests, treatments, and vaccines for lower-income countries.

"We will share more details on supply agreements with these entities as we are able to," Pfizer spokesman Kit Longley said. "We are in continued conversations with a number of private partners and international organizations to provide Paxlovid to lower income countries."

Merck - both on its own and through an agreement with MPP - has deals with dozens of drugmakers to make its pill. Generic versions of molnupiravir are already available in some countries.