What kind of ChangeDetection Strategy are you using?

If it's OnPush, change detection only runs when inputs change or markForCheck() is manually triggered.

Use ChangeDetectorRef.markForCheck() after setting isFollowing:

constructor(private cdr: ChangeDetectorRef) {}

someEvent() {
  this.isFollowing = !this.isFollowing;
  this.cdr.markForCheck();
}