Despite efforts by drug-makers to make them more available, promising Covid-19 treatment pills are likely to take longer to reach patients in low- and middle-income countries than in rich ones due to manufacturing and pricing barriers, according to drug-access advocates and public-health experts.

The pills promise to keep infected people from developing severe disease that necessitates hospitalization. They are already in use in the United Kingdom and are nearing regulatory approval in the United States.

The drugs are expected to play a critical role in the global fight against Covid-19, and they may become even more important if vaccines prove ineffective against the new Omicron variant, as some scientists fear. According to the researchers, the pills are less likely to be affected by Omicron mutations than most leading Covid-19 vaccines.

However, drug-access advocates and public-health experts are concerned that the pills will arrive months later in poor countries, delaying treatment, similar to how the world’s vaccination campaign left many in poor countries unvaccinated after wealthy governments purchased a large portion of the initial supply.

Pfizer Inc., along with Merck & Co. and its partner Ridgeback Biotherapeutics LP, licensed treatment formulas so that generic drug-makers could produce them for poor countries. The companies claim that the agreements will provide supply to governments that cannot afford the more than $500 for a course of treatment that wealthy countries such as the United States pay.

The generic drug-makers, on the other hand, need several months to ramp up production, and the prices they set may still be prohibitively expensive for some poor countries.

Advocates and experts say that most low-income countries lack adequate testing and diagnostic tools to identify patients early enough for treatments to be effective.

“There’s a lot of logistics and training and community health literacy that has to happen for this to work well,” says Brook Baker, a law professor at Northeastern University who works with the Access to Covid-19 Tools Accelerator, a World Health Organization-backed effort to improve access to Covid-19 vaccines, treatments, and diagnostics.

According to studies, subjects must start taking the pills within five days of developing symptoms, making it critical for doctors to quickly identify patients who will benefit.

Most people in developing countries have little to no access to Covid-19 testing, and they often get it only after they are hospitalized. According to the WHO, only 0.4 percent of the three billion tests reported worldwide were performed in low-income countries. According to the organization, only one out of every seven Covid-19 infections in Africa is ever diagnosed.

Separate clinical trials found that both the Pfizer and Merck-Ridgeback drugs reduced the risk of hospitalization and death in high-risk people with mild or moderate disease.

According to physicians and health experts, as home-based treatments, the drugs could fill a significant gap, particularly for unvaccinated people or those who may not respond to shots due to compromised immune systems.

Antibody treatments that have been approved for use, on the other hand, must be administered via infusion or injection at a hospital or doctor’s office and are largely unavailable in many developing countries.

The majority of the publicly announced supply deals have been for rich countries, including the United Kingdom, which approved molnupiravir for use in November. The United States has obtained 10 million courses of Pfizer’s drug and 3.1 million courses of Merck-Ridgeback therapy. Courses are expected to become available in the U.S. shortly after clearance by the Food and Drug Administration, as early as this month.

Pfizer’s pill will not be available in low- and lower-middle-income countries until at least mid-2022, according to Charles Gore, executive director of the Medicines Patent Pool, a United Nations-backed nonprofit that is coordinating manufacturing of the two antivirals with generic companies. This is due to the fact that manufacturers must still set up or repurpose production lines, and governments must approve the pills, according to Mr. Gore.

Most upper-middle-income countries, including Brazil and Russia, where large portions of the population live in poverty, are barred from purchasing generic versions of Merck-Ridgeback or Pfizer pills under Medicines Patent Pool agreements.

The WHO’s ACT-Accelerator, which hosts the Covax program that has been supplying vaccines to developing countries, is also working to help distribute antiviral drugs to countries in need.