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Pfizer starts clinical trial of omicron shot. Biden considers personal sanctions against Putin. Nvidia prepares to abandon Arm purchase. Here’s what you need to know today.

Pfizer is starting a clinical trial of a Covid-19 vaccine that targets the omicron variant. The drugmaker and its German partner, BioNTech, said they were making preparations in case the protection offered by current booster shots wanes. Meanwhile, Israeli health experts have recommended offering a fourth dose of coronavirus vaccine to all adults; the European Union is shifting to a travel model based on vaccination status; China has offered to help Hong Kong with mass testing as the city attempts to stamp out the virus; and hospitalized Covid survivors had an almost five times greater risk of dying in the following 10 months than a sample taken from the general population, according to a new study.