AstraZeneca and Sinopharm clear regulatory hurdles in a week of vaccine milestones.

The world hit a few more pandemic milestones this week with the distribution of the coronavirus vaccines developed by Moderna and by Pfizer and BioNTech; the advancement of trials studying other experimental shots; and the approval or authorization of coronavirus vaccines in several countries. The welcome news comes as the number of known infections worldwide rises toward 83 million.

• Britain announced on Wednesday that it had granted emergency authorization to the Oxford-AstraZeneca vaccine. The vaccine is less expensive than others — $3 to $4 a dose — and can be stored in a normal refrigerator, unlike some of its freezer-bound counterparts, making it easier to transport and administer. The vaccine is meant to be given in two doses four weeks apart, but Britain plans to wait up to 12 weeks to give the second shot, freeing up more doses for first injections. Some early evidence suggests the delay might boost the vaccine’s ability to protect people from Covid-19, though experts have repeatedly cautioned that more data is needed.

• The state-owned Chinese company Sinopharm announced that one of its experimental vaccines, developed by the Beijing Institute of Biological Products, had an efficacy rate of 79 percent based on an interim analysis of Phase 3 trials, spurring the Chinese government to grant the shot full approval. The vaccine has also been approved in the United Arab Emirates and Bahrain. The company has yet to publish the detailed results of its late-stage clinical trials.

• Novavax, based in Maryland, announced on Monday the start of a late-stage clinical trial that will enroll about 30,000 people in the United States and Mexico. Two-thirds of the volunteers in the study will receive the company’s vaccine; the other 10,000 will get a shot of a saline solution as a placebo. Like many other vaccines, Novavax’s vaccine requires two doses. The vaccine can be kept stable in a normal refrigerator.

• The World Health Organization gave the Pfizer-BioNTech vaccine an emergency stamp of approval on Thursday, the first one granted to a Covid-19 vaccine. Placing it on the organization’s Emergency Use Listing will allow the vaccine to move more quickly through regulatory approval in countries around the world. The step will also allow the vaccine to be distributed through Unicef and the Pan-American Health Organization.