One reason for that may be the different types of vaccine being used. Evidence derived from the expanding global inoculation rollout indicates that the messenger RNA shots developed by Moderna Inc. or Pfizer Inc. and BioNTech SE are better at stopping people from becoming contagious, helping reduce onward transmission -- an unexpected extra benefit as the first wave of Covid vaccines were intended to stop people from becoming very sick. Other vaccines, while effective in preventing acute illness or death from Covid, appear not to have this extra perk to the same degree... The differences in effectiveness are already leading to preferred brands in countries where more than one vaccine is available. In the Philippines, immunization centers have been instructed not to announce which shots are being given after a crowd turned up at one location hoping to get access to the Pfizer shot.