The Red Army in January 1942, following it's dramatic victory at Moscow, launched an expanded counteroffensive. One major arm of this was an attack by Northwestern Front's 34th, 11th, and 24th armies again the German 16th army, defending Demiansk and Staraia Rusa. Along with 3rd Shock Army, attacking from the south, they were able to encircle the German II Corps around Demiansk. However, exhausted and understrength, they were unable to reduce the pocket, and a labs corridor was opened in late March.
The POD is that STAVKA, which was extremely frustrated with Volkhov Front's slow progress following it's victory at Tikhvin, decides to commit 2nd Shock Army against German forces around Demiansk, rather than against Lyuban, which IOTL ended in disaster. With these extra forces, the Red Army is able to destroy II Corps, with only small groups breaking out to the west or evacuated by air.
How dies this effect the camaign through the rest of 1942?