Pfizer-BioNTech's omicron-specific vaccine may be delayed, a study finds mixing and matching booster shots may offer more protection against Covid-19, and more in this week's roundup of Covid-19 news.

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• Sanofi and GlaxoSmithKline (GSK) on Wednesday announced they are seeking authorization for their protein-based Covid-19 vaccine from FDA, the European Medicines Agency, and other regulators. According to the companies, their vaccine had a 100% efficacy rate against severe disease and a 75% efficacy rate against moderate-to-severe illness. Its efficacy rate against any symptomatic disease was 57.9%, a figure the companies said mirrored expected vaccine protection against the currently dominant coronavirus variants. Although vaccination rates in western countries have slowed significantly, Sanofi and GSK say its vaccines could be used in low- and middle-income countries or as boosters. In a separate trial, the Sanofi-GSK shot was shown to increase antibody levels between 18 and 30 times when given as a booster. Richard Hatchett, CEO of the Coalition for Epidemic Preparedness Innovations, said protein-based vaccines such as those from Sanofi-GSK and Novavax may "potentially become the workhorse for vaccination in the future" since they are less expensive to produce and can be stored more easily than mRNA vaccines. "These are very important vaccines," he added. (Roland, Wall Street Journal, 2/23)

• CDC on Tuesday updated its Covid-19 vaccine guidance to recommend an eight-week interval between first and second shots of the Pfizer-BioNTech and Moderna vaccines for certain groups. The updated guidance applies to some people older than 12, particularly boys and men between ages 12-39. According to the New York Times, CDC made the change after research showed that a longer interval between doses can increase vaccine effectiveness and reduce the risk of myocarditis, a serious but uncommon side effect. "While absolute risk remains small, the relative risk for myocarditis is higher for males ages 12-39 years, and this risk might be reduced by extending the interval between the first and second dose [of mRNA vaccines]," CDC said. Although public health experts say the longer interval between doses may increase a person's risk of being infected after just one shot, the change could also reassure some unvaccinated people and parents who are worried about the potential risk of myocarditis. "If the message is, 'We already have a highly effective and highly safe vaccine or vaccines, and this is an approach to make them even safer,' that might convince some folks," said Matthew Daily, a senior investigator at Kaiser Permanente in Colorado and a member of CDC's advisory committee. (Imbler, New York Times, 2/23; Choi, The Hill, 2/23)

• Individuals who received a Covid-19 booster that was a different brand than their primary vaccine doses may be better protected against the coronavirus, according to a study from Singapore published in JAMA. For the study, researchers used data from the Singapore Ministry of Health to analyze Covid-19 incidence and severity among individuals ages 60 and older eligible to receive booster shots between Sept. 15 and Oct. 31, 2021. Out of more than 703,000 eligible individuals, 576,132 received either Pfizer-BioNTech or Moderna boosters. Overall, people who mix-and-matched their boosters had a lower Covid-19 incidence rate per million person-days than those who received the same vaccine brand as a booster. People who received Pfizer-BioNTech for their primary series and booster had a Covid-19 incidence rate of 227.9 per million person-days, compared with 147.9 for those who received a Pfizer-BioNTech primary series and a Moderna booster. Similarly, people who received a Moderna primary series and booster had an infection incidence rate of 133.9 per million person-years, compared with 100.6 for those with a Moderna primary series and a Pfizer-BioNTech booster. "The study results support recommendations for vaccine boosters and suggest that heterologous boosting may provide greater protection against Covid-19," the researchers concluded. (Bean, Becker's Hospital Review, 2/15)

• The United Kingdom will begin offering a fourth dose of Covid-19 vaccines to certain vulnerable populations in the spring. According to U.K. health officials, the additional dose will be available to individuals ages 75 and older, individuals in care homes for older adults, and immunocompromised individuals ages 12 and older. "We know immunity to Covid-19 begins to wane over time," said U.K. Health Secretary Sajid Javid. "That's why we're offering a spring booster to those people at higher risk of serious Covid-19 to make sure they maintain a high level of protection. It's important that everyone gets their top-up jabs as soon as they're eligible." A broader booster shot campaign for other groups at high risk of severe outcomes could also be implemented in the fall, The Hill reports. Currently, U.S. health officials are not recommending a fourth dose, except for immunocompromised people, but the possibility of an additional dose continues to be discussed. (Sullivan, The Hill, 2/21)

• Pfizer-BioNTech have announced that their omicron-specific Covid-19 vaccine may be delayed by several weeks due to the extended time it is taking the companies to gather data. The companies began clinical trials of their omicron-specific last month, and initial study results were expected in the first half of the year. BioNTech CEO Ugur Sahin said that once the vaccine is produced, the company will assess if the omicron-specific vaccine is still necessary, since the number of Covid-19 infections from omicron around the world have dropped significantly over the past few weeks. However, he noted that "[i]f the wave ends, that does not mean it can't begin again." In addition, Sahin said BioNTech would continue to be prepared to modify its Covid-19 vaccine if needed if new coronavirus variants of concern emerge in the future. (Breslin, The Hill, 2/17)