The UN health agency Friday "strongly recommended" the use of nirmatrelvir and ritonavir, sold under the name Paxlovid, for mild and moderate Covid patients at the highest risk of hospital admission.

The oral antiretroviral drug was developed by Pfizer and is "the best therapeutic choice for high-risk patients to date," the World Health Organization (WHO) said.

The recommendation is based on new data from two randomised controlled trials involving more than 3,000 patients that found an 85 percent reduction in the risk of hospitalisation.

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However, the WHO said availability, lack of price transparency in bilateral deals made by the producer, and the need for prompt and accurate testing before administering it are turning this life-saving medicine into a major challenge for low- and middle-income countries.

One obstacle for low- and middle-income countries is that the medicine can only be administered while the disease is at its early stages, making prompt and accurate testing essential for successful outcomes.

Improving access to early testing and diagnosis in primary health care settings will be key for the global rollout of this treatment, the UN agency said.

Lack of transparency on the part of the originator is making it difficult for public health organisations to get an accurate picture of the medicine's availability, as well as which countries are involved in bilateral deals and what they are paying.

Also, a licencing agreement between Pfizer and the UN-backed Medicines Patent Pool limits the number of countries that can benefit from the generic production of the medicine.

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The UN agency strongly recommended that Pfizer make its pricing and deals more transparent.

The pharmaceutical giant was also urged to enlarge the geographical scope of the licensing agreement so that more generic manufacturers can produce the medicine and make it available faster at affordable prices.

The WHO also updated its recommendation on another antiviral medicine, remdesivir, suggesting that it can be used in mild or moderate Covid patients who are at risk of hospitalisation.