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Covid-19 vaccinations at Lichfield Cathedral covidin Staffordshire, UK

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WHEN Margaret Keenan became the first person to receive a covid-19 vaccine outside a trial last December, she was among the 7 in 10 people surveyed globally who said they would be willing to receive a dose. But the significant minority unwilling to have a vaccine led public health experts to worry about how such hesitancy might hamper efforts to achieve herd immunity.

The good news is that with more than 400 million people around the world having received at least one dose of a vaccine, …