They have been fined and banned from all rugby league related activity, including training and games, for 14 days.
Hastings, however, will not miss any games as his ban has been backdated to his breach on August 7 and the period of suspension has already elapsed.
The former Salford half-back did play twice for the Warriors during his suspension period of August 8-21 – in Super League games against Wakefield and Leeds – but his transgression had not come to light then, nor had the RFL made clear the punishments for breaches.
The governing body has stepped up monitoring since 12 members of staff, including nine players, at Hull tested positive for coronavirus a fortnight ago.
Gavet is suspended from August 14-27 for a breach on August 13 and Dean from August 17-30 for a breach on August 16.
A statement from the RFL said the 14-day ban “is consistent with the self-isolation period required following close contact with a person who had tested positive for Covid-19”.
It added: “Bans will begin from the date of the transgression, irrespective of when the sanction is imposed.”
RFL chief regulatory officer Karen Moorhouse said: “COVID protocols were established in the weeks leading up to the resumption of the Betfred Super League season earlier this month, with an emphasis on player education and collective buy-in, and with clubs encouraged to agree and enforce their own codes of conduct.
“In the main the protocols have been observed, and we are grateful to the majority of clubs and players and other individuals involved for their responsible and disciplined approach.
“However we are in a situation where breaches of the protocols by any individuals connected with the game could have serious repercussions for all – either an impact on individual and public health, or in terms of disruption to the rescheduled fixtures list.
“It is therefore important that appropriate sanctions reflecting the reasons for the regulations are imposed. The ability to enforce a 14-day stand-down reflects this.”
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