Pfizer Inc. and BioNTech SE’s messenger RNA vaccine lost effectiveness in the first 90 days after full vaccination, though that shot and the one made by AstraZeneca Plc still staved off a majority of Covid infections. When vaccinated people did get infected with delta, they had similar levels of virus in their bodies as those who hadn’t had their shots, backing up a recent assessment by the Centers for Disease Control and Prevention.
The results are likely to fuel calls to give booster shots to the fully vaccinated even as countries around the world still lack enough supply for first immunizations. The U.S. on Wednesday said Americans who got both doses of the Pfizer-BioNTech or Moderna Inc. mRNA vaccine will be able to get a third one after eight months. U.K. authorities are still deciding how broadly boosters should be given. In Israel, which started giving third doses of Pfizer-BioNTech this month, initial results show they have been 86% effective for people over the age of 60.
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