The DWP has said-
'Statutory Sick Pay (SSP) is available from the first day of absence to individuals who are unable to work because they have been advised to shield, for example where they can’t work from home...If someone is clinically extremely vulnerable (CEV), they should not work outside the home while shielding is in place. If they cannot work from home, they should speak to their employer to see if there are any alternative arrangements that can be made e.g. using the Coronavirus Job Retention Scheme'.'