Novavax begins early-stage tests of a combined flu and Covid-19 vaccine, a study finds reducing the U.S. prison population could have prevented millions of Covid-19 cases, and more in this week's roundup of Covid-19 news.

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• According to a pre-print study from Israel, adults who received an additional dose of Pfizer-BioNTech's Covid-19 vaccine are 11 times less likely to be infected with the coronavirus 12 or more days post-"booster." In the study, researchers analyzed data from more than 1 million people ages 60 or older who received a third vaccine dose at least five months after their second dose. The researchers also found that participants were more than 10 times less likely to develop severe Covid-19 after the third dose. However, the researchers noted that the data is preliminary, has limitations, and the findings need to be confirmed with further studies. (Adams, Becker's Hospital Review, 9/2)

• COVAX, a Covid-19 vaccine equity program backed by the United Nations, on Wednesday reduced its expected end-of-the-year vaccine deliveries from 1.9 billion doses to 1.425 billion doses. According to Axios, several problems likely contributed to this reduction in doses, including production issues with the AstraZeneca and Johnson & Johnson vaccines and export restrictions in India. "COVAX is making strenuous efforts to address and mitigate these risks," the program said. Currently, COVAX has delivered 245 million vaccines doses, primarily to poorer countries, the New York Times reports. (Chen, Axios, 9/8; Mueller/Slotnik, New York Times, 9/8; Coleman, The Hill, 9/8)

• A large, randomized study from Stanford Medicine and Yale University offers "the strongest evidence yet" that surgical masks can effectively reduce the spread of Covid-19, Becker's Hospital Review reports. The eight-week study involved 342,126 participants in 600 villages across rural Bangladesh who were randomly assigned to either a control or intervention group. In the intervention group, participants received masks that they were encouraged to wear and educational materials about why masking was important. The researchers found that participants in the intervention group were around 11% less likely to get Covid-19 compared to the control group. This risk reduction was even more pronounced among older adults. Specifically, people over the age of 60 who wore masks were 35% less likely to get Covid-19 than those who did not. "We now have evidence from a randomized, controlled trial that mask promotion increases the use of face coverings and prevents the spread of Covid-19," Stephen Luby, a professor of medicine at Stanford and one of the study's authors, said. "This is the gold standard for evaluating public health interventions. Importantly, this approach was designed [to] be scalable in lower- and middle-income countries struggling to get or distribute vaccines against the virus." (Bean, Becker's Hospital Review, 9/2)

• The World Health Organization (WHO) on Wednesday reiterated a call for wealthy nations to refrain from administering booster doses until more of the worldwide population is vaccinated. Previously, WHO's Director-General Tedros Adhanom Ghebreyesus called for a moratorium on booster doses through September, but has now extended his plea through at least the end of the year, in the hopes that every country can vaccinate at least 40% of its population. "We have been calling for vaccine equity from the beginning, not after the richest countries have been taken care of," he said. "I will not stay silent when companies and countries that control the global supply of vaccines think the world's poor should be satisfied with leftovers." In addition, while Tedros acknowledged the necessity of additional doses for at-risk populations, such as the immunocompromised, he said there should not be "widespread use of boosters for healthy people who are fully vaccinated." Currently, several countries, including Israel, the United Kingdom, France, and the United States, have either begun or are planning to offer booster doses to certain populations. (Keaten, Associated Press, 9/8; Weixel, The Hill, 9/8)

• Novavax this week announced that it is beginning early-stage tests of a combined flu and Covid-19 vaccine. According to The Hill, 640 healthy adults between age 50 and 70 will participate in the trial, which will be conducted at 12 study locations in Australia. Participants will receive two doses of the combined shot, one at the beginning of the trial and the second 56 days later. "This study is the first-of-its-kind to evaluate the vaccine's potential to induce a robust immune response ... against two life-threatening diseases simultaneously," said Gregory Glenn, the company's president of research and development. He added, "The combination of these two vaccines, which have individually delivered outstanding results with favorable safety and tolerability profiles, may lead to greater efficiencies for the health care system and achieve high levels of protection against COVID-19 and influenza with a single regimen." The trial's results are expected to be released in the first half of 2022, The Hill reports. (Lonas, The Hill, 9/8; Gilgore, Washington Business Journal, 9/8 [subscription required])

• A new study published in JAMA Network Open suggests that further reduction of the U.S. prison population could have prevented millions of Covid-19 cases. According to a summary of the study, U.S. prisons "have effectively become infectious disease incubators," putting the country at greater risks for outbreaks. In the study, researchers analyzed data from January to November 2020 in 1,605 counties across the U.S. While most prisons reduced their populations at rates between 20% and 50%, the researchers found that an 80% reduction in the U.S. jail population would have reduced the country's daily growth of rate of Covid-19 cases by 2%. According to Eric Reinhart, a researcher from the Northwestern University Feinberg School of Medicine who worked on the study, "[E]ven just a 2% reduction in daily case growth rates in the U.S. from the beginning of the pandemic until now would translate to the prevention of millions of cases." (Chappell, NPR, 9/2)