“They had little chance to escape the bug while working in hot and cramped conditions.”
This was a Vanguard-class submarine, not a Type VII U-boat. A large, modern submarine such as the Vigilant is neither cramped nor hot. Unless working in the propulsion spaces, a crew member is likely to be wearing a sweater or coat.
As for the claim of higher viral load risk, the opposite might be true. A modern submarine has a robust, high-filtration ventilation system that would rapidly dilute any airborne virus.
“It was a calculated risk.” And the risk was very low.