. @CMO_England gave a simple clear public health justification for extending the gap between the two necessary vaccine doses to three months: widening the gap will allow twice as many people to be vaccinated than would otherwise be the case; and even the first dose...

gives "significantly more" than.50% protection against the virus. Ergo, there is a net benefit from giving lesser vaccine protection to more people. But Whitty does accept that by widening the gap between doses the risk of what he calls "an escape mutant" would be increased...

(that is the virus would mutate and build up resistance to the existing vaccines - which would be something of a setback). However he sees that risk as worth taking because it is "sufficiently small" compared with the benefits of vaccinating more people more rapidly. And...

his colleague @uksciencechief added that he believes the new Messenger RNA vaccine technology would allow relatively fast development of new and refined vaccines to cope with whatever mutant strains we may encounter in the months and years ahead. Here's hoping.

PS please ignore the stray full stop in the first sentence of second tweet in this thread