Up to six different Covid-19 boosters were found to be safe, and provoked strong immune responses in people who have previously received a two-dose course of the Oxford-AstraZeneca-developed Covishield, or Pfizer-BioNTech’s BNT162b2, the first randomised phase 2 trial of boosters given after two doses of either vaccine, published in The Lancet shows.Up to six different Covid-19 boosters were found to be safe, and provoked strong immune responses in people who have previously received a two-dose course of the Oxford-AstraZeneca-developed Covishield, or Pfizer-BioNTech’s BNT162b2, the first randomised phase 2 trial of boosters given after two doses of either vaccine, published in The Lancet shows.