Giving the first dose of the Covid-19 vaccine but delaying the second dose among people younger than 65 could lead to fewer people dying from the disease, but only if certain conditions are met, a predictive modelling study showed.

As the coronavirus pandemic continues, there is debate over whether to extend the gap between doses to give as many people as possible some protection or stick to the intervals designated in clinical trials.

For example, Pfizer has said there is no...