Medicare open enrollment starts today and although the swiftly growing market remains stable overall, insurers are making a flurry of changes that could leave some senior citizens hunting for new policies, paying more out of pocket or getting skimpier supplemental benefits. The shifts come as Medicare Advantage enrollment is expected to hit 35.7 million, or 51% of total Medicare enrollment. However, few enrollees shop during open enrollment, which runs until December 7. Nearly two-thirds of Medicare Advantage participants did not compare their coverage with other options for 2022, according to a recent analysis by KFF.