Omicron is already altering the way medicine combats COVID-19.

Despite the fact that it has only recently become widespread in the United States, doctors, pharmacists, and pharmaceutical companies have stated that they require different tools to combat the new variant.

It is unlikely that two widely used monoclonal antibodies will be effective against omicron. In their place, the government has accelerated the approval of two antivirals that can be taken immediately after diagnosis to prevent illnesses from worsening.

The Food and Drug Administration approved the use of Pfizer’s Paxlovid, a home-based pill regimen that prevents nearly 90% of severe COVID-19 in those at high risk. On Thursday, the FDA approved the use of molnupiravir, a second antiviral that appears to prevent the progression to severe disease about 30% of the time.

The challenge will be getting antivirals to those who require them. Paxlovid takes 6 to 8 months to manufacture, and while deliveries will begin almost immediately, only 265,000 treatment courses will be available until the end of January, according to Zients at a news conference on Wednesday.

According to Merck, which manufactures the drug with Ridgeback Biotherapeutics, ten million doses of molnupiravir are ready to be packaged and distributed, and hundreds of thousands of doses should be available within days.

COVID-19 infections have increased by 36% in the last week, and some predict a significant increase in cases over the next few weeks, possibly exceeding the surge this time last year. Although omicron may cause less severe disease than its predecessors, it is likely that many high-risk people will become infected.

According to a number of doctors, the Paxlovid approval is especially welcome because omicron has rendered their main tool for keeping people out of the hospital ineffective. “We’ve stopped scheduling monoclonal infusions in New York,” said Dr. Daniel Griffin, chief of infectious diseases for ProHealth Care, which has 300 locations in and around New York City.

Monoclonal antibodies, which are drugs derived from people whose immune systems successfully fought off COVID-19, have been extremely effective in preventing severe disease in high-risk infected people. However, neither that drug nor a similar one from Eli Lilly, which both target the spike protein on the virus’s surface, are expected to work against the heavily mutated omicron variant.

Griffin said his colleagues are scrambling to get enough sotrovimab, a third monoclonal antibody that targets a different spot on the virus and appears to still work against omicron but is in short supply.

“We have maybe 2,000 doses in all of downstate New York,” he said, adding that he may have to decide whether to give his share of those sotrovimab doses to high-risk patients who haven’t been vaccinated, or to those who have received two or three shots but may not be fully protected due to weakened immunity.

According to spokesperson Kathleen Quinn, GlaxoSmithKline, which manufactures the drug with Vir Biotechnology, is “working with urgency and exploring options to expand our supply capacity.”

In June, the companies demonstrated that sotrovimab reduced the risk of needing hospitalization for more than a day or dying from any cause within a month by 79 percent when compared to placebo.

The government has spent $1 billion on sotrovimab doses that will be provided free of charge to those in need. It is expected to cost around $2,100 per treatment course, similar to other monoclonals. Sotrovimab, like most monoclonal antibodies, is administered via a 30-minute infusion, which has been difficult to deliver during the pandemic because it necessitates dedicated facilities where highly infectious COVID-19 patients can be isolated from others.

Griffin and Gandhi are both eager to get their hands on Paxlovid. “That could be a very timely and appealing way to treat people, particularly those who are at high risk of progression,” Gandhi said.

They were less enthusiastic about molnupiravir, which is aimed at the same high-risk group, but said they would use it if no other option was available.

Molnupiravir was found to be 30% effective at preventing severe disease, after being found to be 50% effective in an earlier study.

Many people, including those over 65, those with obesity, diabetes, or lung disease, and those with compromised immune systems, are at a higher risk of severe disease if infected.