One shot of the Oxford/AstraZeneca or Pfizer/BioNTech vaccine reduces coronavirus infections by nearly two-thirds and protects older and more vulnerable people as much as younger, healthy individuals, a study has found.
The results from Oxford University and the Office for National Statistics are a welcome boost to the vaccination programme and the first to show the impact on new infections and immune responses in a large group of adults in the general population.
By driving down rates of infection the vaccines will not only prevent hospitalisations and deaths but help break chains of transmission and so reduce the risk of a damaging resurgence of disease as the UK reopens.
The researchers analysed Covid test results from more than 350,000 people in the UK between December and April. They found that 21 days after a first jab – the time it takes the immune system to mount a decent response – new Covid infections dropped by 65%.
The vaccines were more effective against symptomatic than asymptomatic infections, reducing rates by 72% and 57% respectively, compared with those seen in the unvaccinated population.
A second shot of the Pfizer vaccine boosted protection further, causing symptomatic infections to fall by 90% and asymptomatic infections by 70%. Because the Oxford vaccine was approved and rolled out later, it is too early to assess the impact of those second doses.
Scientists on the team said the findings supported the UK’s decision to prioritise giving first shots to elderly and more vulnerable people by delaying second doses. “There was no evidence that the vaccines were less effective among older adults or those with long-term health conditions,” said Dr Koen Pouwels, a researcher on the team.