About half of infections in an outbreak of the Delta variant of Covid-19 in Israel were in people who were fully inoculated with the Pfizer Inc. vaccine, prompting the government to reimpose an indoor mask requirement and other measures to contain the highly transmissible strain. Preliminary findings by Israeli health officials suggest about 90% of the new infections were caused by the Delta variant, according to Ran Balicer, who leads an expert advisory panel on Covid-19 for the government. Around half of those infected were fully vaccinated, he said. Israel is now reassessing its Covid-19 regulations after moving to open up its society and economy after multiple lockdowns last year. “The entrance of the delta variant has changed the transition dynamics,” said Prof. Balicer, who is also the chief innovation officer for Israel’s largest health-management organization, Clalit.