As a lot of people are aware, vaccines produced by different pharmaceutical companies have different “efficacy rates”:For example, this chart from the BBC which shows different rates of how effective vaccines are. My question is, are there different measures of how effective a vaccine are?

e.g.- Are they measured according to how many people, as a percentage, receive immunity? Is it measured according to who retains immunity after trials?

A secondary question is do different pharmaceutical companies have a standard for measuring how effective their vaccines are, or do they each set their own standards? (with or without help from the WHO, etc?)


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