Spring Offer: Get 1 Year, Save 58%

Hyon Xhi Tan

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Three vials with different vaccines against Covid-19 by (L-R) Moderna, Pfizer-BioNTech and AstraZeneca stand on a table. (THOMAS KIENZLE/AFP via Getty Images)

Which COVID vaccine is best? Here’s why that’s really hard to answer

Wen Shi Lee, Hyon Xhi Tan