It's been almost a month since Sen. Mitch McConnell (R-Ky.) last shared a health update, leading to another round of speculation about when -- or if -- he will return to Congress, but experts say recovery from pneumonia in people McConnell's age can take time.

The 84-year-old politician hasn't been seen in public in nearly 3 months. According to official statements, McConnell was hospitalized after a fall in June, contracted pneumonia soon after, and following a stint at a rehab facility was discharged last month to continue physical therapy at home.

Pneumonia can range from mild cases where patients often bounce back quickly after intravenous and oral antibiotics to severe cases complicated by sepsis, said John Rowe, MD, a professor of health policy and aging at Columbia University in New York City.

Lung and immune system functions weaken with age, putting older patients like McConnell at particular risk, he told MedPage Today. "All these risks are magnified if the patient has a pre-existing condition -- in this case, the residua of childhood polio -- which may cause loss of muscle mass and strength," said Rowe.

Patients with pneumonia usually make a full recovery, but for people in their mid-80s like McConnell, "it can be very debilitating, with recovery to full strength and activity requiring as much as 6 months," he added.