The maximum squad size has been raised from 23 to 26 players, while managers will be able to make five substitutions per match instead of three.
Should England have, for example, six players isolating at one time, the depth of their squad should allow a starting XI to be named along with nine substitutes.
Teams must fulfil their tournament fixtures if they have a minimum of 13 available players.
Should more than half of a 26-man squad be in isolation, games can be postponed and rescheduled by Uefa within 48 hours, if it allows a team to reach the 13-man threshold. They can potentially be relocated.
If a team that is severely afflicted by Covid-19 has no immediate prospect of playing, they will forfeit the match and their opponents will be awarded a 3-0 win.
Any player who tests positive must immediately isolate from the rest of the squad to contain the outbreak.
Team-mates or staff deemed to have had close contact with the infected players must do the same.
Scotland, Spain and Sweden have all seen players forced to isolate ahead of the tournament.
Sweden's squad have been subjected to stricter Covid-19 measures after forward Dejan Kulusevski and midfielder Mattias Svanberg tested positive earlier this week.
A series of measures have been adopted, including daily antigen tests and an increased number of PCR tests. Indoor meetings are being held in smaller groups and in the biggest rooms available at their training camp.
Time limits have also been set on players receiving treatment with sessions to be held outdoors if possible.
On Wednesday, Spain brought in six standby players - including Leeds United striker Rodrigo - in a separate training 'bubble' as a precautionary measure after positive tests in their main squad. They also added 11 under-21s to the bubble.
If a player in the main squad is replaced, they cannot later be recalled.
Support The Yorkshire Post and become a subscriber today. Your subscription will help us to continue to bring quality news to the people of Yorkshire. In return, you'll see fewer ads on site, get free access to our app and receive exclusive members-only offers. Click HERE to subscribe.