The 35-year-old was out of favour under former Hoops manager Mark Hughes after the arrivals of Esteban Granero and Park Ji-Sung edged him down the pecking order.
“Harry’s got everyone believing again,” Derry told QPR’s website.
“There’s a togetherness about us now. The team spirit – which comes through runs like this – is improving all the time.
“We’re all coming together at the moment. We’re showing that togetherness that is required.”
Derry has made 91 appearances for QPR after completing a free transfer to Loftus Road from Crystal Palace in 2010, scoring his first league goal for the club in a 3-2 win against Liverpool earlier this year.
And the veteran has set a target of making a century of appearances for the Hoops before his new deal expires in 2014.
“I’m determined to hit that landmark figure. That will be a fantastic achievement,” he added.
“People who have followed me throughout my career will notice that I’ve moved on every two or three years, but when you hit that 100 game mark it’s a fantastic milestone.”