Because the vaccine may not stop transmission of the virus.

The efficacy of vaccines is estimated from trials, using statistical techniques.

Like any medical drug, vaccines are tested in large-scale randomised controlled trials.

Modelling shows that old and vulnerable people should be prioritised.

We can't say for sure, but everything depends on how many people agree to be vaccinated.

We are all longing to go into a lower tier, but this can come at a high price later on.

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