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Astra Shot Better at Stopping Covid Than Slowing Transmission

  • Vaccine reduced asymptomatic infections by 27%, study shows
  • Lancet report confirms vaccine’s 70% efficacy against illness
A heath worker prepares to inject the Covid-19 trial vaccine into a patient.
Photographer: Andrey Rudakov/Bloomberg

A vaccine from the University of Oxford and AstraZeneca Plc shows only a limited ability to stop transmission of the coronavirus despite preventing Covid-19 illness in a majority of those who are infected.

As promising vaccine data keeps rolling in, one of the central unanswered questions has been whether inoculations can not only stop people from getting sick but also slow the spread of the virus, a key element for reopening economies.