FDA authorizes Pfizer's and Merck's Covid-19 pills, Israel offers a fourth dose of Covid-19 vaccines for some citizens, and more in this week's roundup of Covid-19 news.

300+ Covid-19 treatments are in development. Which ones will really matter?

• FDA on Wednesday authorized Pfizer's Covid-19 antiviral pill, Paxlovid, for high-risk patients ages 12 and older. "This authorization provides a new tool to combat Covid-19 at a crucial time in the pandemic as new variants emerge," said Patrizia Cavazzoni, director of the FDA's drug division. Separately, Eric Topol, director of the Scripps Research Translational Institute, said, "It's the biggest thing to happen in the pandemic after vaccines." Although Paxlovid will be available at pharmacies and hospitals in the coming days, initial supply will be limited. In addition, FDA on Thursday authorized Merck's Covid-19 pill, molnupiravir, for adults at high risk of severe disease. However, the agency recommended using the Merck drug only if other authorized drugs aren't available or medically appropriate, the Wall Street Journal reports. The United States has already ordered 10 million of Pfizer's antiviral pill, and around 3 million of Merck's. (Beals, The Hill, 12/21; Hopkins/Walker, Wall Street Journal, 12/22; Hopkins/McKay, Wall Street Journal, 12/23)

• Three separate teams of scientists from South Africa, Scotland, and England released preliminary research suggesting that omicron may cause milder cases and result in fewer hospitalizations than the delta variant, the New York Times reports. The researchers said omicron may result in milder cases because of the variant's distinct biological features, but they also acknowledged that the overall lower risk of hospitalization associated with omicron—compared with delta—could be due to existing immunity in the studied populations. Specifically, when compared with delta, the risk of hospitalization among those infected with omicron was about 70% lower in the South African study, about two-thirds lower in the Scottish study, and about 20% lower in the English study. The studies controlled for various confounding factors, including age, vaccination status, and prior infection; however, the researchers noted the results are still preliminary. (Anthes/Zimmer, New York Times, 12/22; Ungar/Stobbe, Associated Press, 12/23; Kew, Bloomberg, 12/22)

• Omicron may have the shortest incubation period of any Covid-19 variant, according to a research paper published last week in Eurosurveillance. While the incubation period for the delta variant is estimated to be around four days, preliminary research suggests that the incubation period for the omicron variant is just three days. In the research paper, the authors analyzed an outbreak of roughly 80 people that originated at a restaurant in Norway. Notably, almost every person who had been infected with the omicron variant was vaccinated and had received a negative antigen test result within two days before the event. After the party, their symptoms appeared in around three days. Although the research findings are preliminary—and may not represent the general population—they seem to align with anecdotal reports from other sources, according to Becker's Hospital Review. According to Omai Garner, director of clinical microbiology at UCLA Health, "If omicron has a shorter incubation period, that's going to wreak havoc on how we test for it and deal with it." (Masson, Becker's Hospital Review, 12/21)

• The European Commission on Monday authorized Novavax's Covid-19 vaccine after a scientific committee said the shot, known as Nuvaxovid, was safe and effective—making it the fifth vaccine available in the European Union. Nuvaxovid, which is a protein-based vaccine, was found to be 90.4% effective in a Phase 3 trial involving 29,960 participants across 119 locations in the United States and Mexico. "At a time where the omicron variant is rapidly spreading, and where we need to step up vaccination and the administration of boosters, I am particularly pleased with today's authorization of the Novavax vaccine," said Ursula von der Leyen, president of the European Commission. Novavax plans to seek FDA authorization of its vaccine by the end of the year. (Zimmer, New York Times, 12/20; Roland, Wall Street Journal, 12/20; Lawler, Axios, 12/21; Adams, Becker's Hospital Review, 12/17)

• Moderna on Monday released preliminary data showing that its FDA-authorized, 50-microgram Covid-19 booster dose increases the level of antibodies that protect against the omicron variant by 37-fold compared with pre-booster levels. Research also suggested that a 100-microgram booster dose was even more effective at protecting against omicron, producing an 83-fold increase in antibody levels. "To respond to this highly transmissible variant, Moderna will continue to rapidly advance an omicron-specific booster candidate into clinical testing in case it becomes necessary in the future," said Moderna CEO Stéphane Bancel. (Mandavilli, New York Times, 12/20; Diaz, NPR, 12/20; Axios, 12/20)

• Pfizer and BioNTech on Friday announced that their Covid-19 vaccine did not yield a strong immune response among children ages two to five in ongoing clinical trials—a setback that could prevent children under five from getting the vaccine until next year. Still, the companies said they plan to apply for the use of their vaccine in children under the age of five early next year as they test the use of a third dose. "The decision to evaluate a third dose of 3 µg for children 6 months to under 5 years of age reflects the companies' commitment to carefully select the right dose to maximize the risk-benefit profile," the companies said. "If the three-dose study is successful, Pfizer and BioNTech expect to submit data to regulators to support an emergency use authorization for children 6 months to under 5 years of age in the first half of 2022." (Mandavilli/Robbins, New York Times, 12/17; Sullivan, The Hill, 12/17)

• Regeneron Pharmaceuticals last week said that its antibody therapy, which is used to prevent severe illness in unvaccinated Covid-19 patients, exhibits "diminished" potency against the omicron variant. However, AstraZeneca said its monoclonal antibody treatment, called Evusheld, "retained neutralizing activity" against omicron in a lab study conducted by independent FDA investigators. According to the company, these findings add to "the growing body of preclinical evidence demonstrating that Evusheld retains activity against all tested variants of concern to date." (Vakil, The Hill, 12/16; Bella, Washington Post, 12/16; Mueller, New York Times, 11/30; AP/Modern Healthcare, 12/19)

• Israeli Prime Minister Naftali Bennett on Tuesday announced that fourth doses of a Covid-19 vaccine will be authorized for residents over the age of 60, as well as for health care workers and individuals with compromised immune systems—making it the first known country to offer a fourth Covid-19 vaccine dose. "The citizens of Israel were the first in the world to receive the third dose of the Covid-19 vaccine and we are continuing to pioneer with the fourth dose as well," said Bennett. Notably, Pfizer executives earlier this month said the new omicron variant could increase the likelihood that individuals will need a fourth coronavirus vaccine dose sooner than expected, as the new variant may evade some existing vaccine antibodies. In Israel, a fourth dose for those who are eligible will be administered at least four months after their third doses. (Jeong et al., Washington Post, 12/9; Axios, 12/21; Lieber et al., Wall Street Journal, 12/22)