With a seductive number, AstraZeneca study fueled hopes that eclipsed its data

A new paper released this week suggested that a vaccine developed by AstraZeneca and Oxford University not only protected clinical trial participants from developing disease, but also may significantly reduce transmission of the virus that causes the disease.

In the recent burst of data on Covid-19 vaccines, that suggestion stood out. The question of whether Covid-19 vaccines reduce transmission has been a critical and unanswered one, creating uncertainty over whether people who have been vaccinated will still be able to be infected by and transmit onward SARS-Cov-2, the virus that causes Covid, to those who have not yet been vaccinated.