Advisers say early action could save later, tougher measures to stop the spread of coronavirus.
Fewer adults are practising social distancing than think it is important, figures for Great Britain show.
She is "in good spirits" after a one-night stay for preliminary medical checks, Buckingham Palace says.
Five officers have cases to answer over messages sent on WhatsApp and Signal, the police watchdog says.
No 10 calls the practice "unacceptable", but wants new guidance for employers rather than a law.