Six months of COVID vaccines: What 1.7 billion doses have taught scientists

Over the past six months, hundreds of millions of people around the world have rushed to follow in the footsteps of a 90-year-old British woman named Margaret Keenan.

At 6:30 a.m. on 8 December 2020, Keenan became the first person to receive a COVID-19 vaccine as part of a mass vaccination effort. Her shot was the culmination of a frenzied effort to develop vaccines safely and in record time. Now, more than 1.7 billion doses later (see ‘Global doses’), researchers are sifting through the data to address lingering questions about how well the vaccines work — and how they might shape the course of the coronavirus pandemic that has already taken more than 3.5 million lives.