Dear Doctor: Our daughter is 5 months old, and we always put her to sleep on her back. Lately, when we check on her, she’s on her stomach. Should we be keeping an eye out and positioning her on her back again when that happens?

Dear Reader: First, congratulations on your daughter hitting an important developmental milestone! Rolling over, which typically occurs anywhere from the ages of 4 to 6 months, is an important part of a baby’s development. It’s one of the first steps on the journey to your baby becoming mobile. Your daughter is gaining in both muscle strength and coordination; that gentle rocking from side to side that you have noticed has now become forceful enough that she is able to flip herself over.

It’s true that since 1994, the American Academy of Pediatrics (AAP) has recommended that parents put babies to sleep on their backs. This is to prevent sudden infant death syndrome (SIDS), the unexpected and unexplained death of an apparently healthy baby, often during sleep.

The exact cause of SIDS remains unknown. However, researchers believe that it may occur when an infant’s airway becomes blocked for some reason, and the part of their brain that would normally wake them up isn’t developed enough yet, or isn’t functioning properly. The “Back to Sleep” campaign, which began in 1994 to urge parents to place sleeping infants on their backs, has helped significantly reduce SIDS deaths in the United States.

Here’s the good news: Now that your daughter is able to turn herself over unaided, her brain has developed enough that she will shift position should she experience any problems with breathing. The National Institutes of Health recommend -- and we agree -- that you should continue to start her out on her back when she’s going down for a nap or for the night. Should she turn over during her sleep, it’s fine -- you don’t need to reposition her on her back.

There are a few other simple precautions you can take to ensure a safe and comfortable sleep environment for your infant. First, make sure she’s lying on a firm mattress with a fitted sheet. Don’t cover her with loose bedding, such as a sheet, blanket or quilt. Instead, dress her in just enough sleep clothing to keep her comfortable throughout the night. Although she may need to fall asleep with her favorite pillow or stuffed toy, once she’s nodded off, keep her bed clear of them and other soft objects.

Overheating has been suspected to play a role in SIDS, so it’s important that your baby’s bedroom remain at a comfortable temperature. If your sleeping baby’s chest feels hot to the touch, or if they’re sweating, they may be too warm. To stave off potential problems, it’s recommended that babies sleep in their parents' bedroom -- in their own crib or bassinet, not in the parental bed -- until they’re at least 6 months old.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Hello again, dear readers, and welcome to our monthly letters column. We’re happy to hear that our recent focus on your questions regarding the coronavirus vaccines has been helpful. Keep sending them in, and we’ll keep addressing them. Speaking of which:

-- A reader with a petite friend wondered whether coronavirus vaccines should be tailored to a person’s physical size. “My neighbor weighs 94 pounds and worries she might get too much vaccine with a standard vaccination,” she wrote. “Should she get a smaller dosage?” Adults of all sizes can safely receive the same vaccine dose. Although medications are calibrated to reach certain blood concentrations based on body weight, the coronavirus vaccines “speak” directly to the immune system. That means the dosage remains constant, no matter a person’s size. Your neighbor can safely receive the standard dose of any of the three coronavirus vaccines available in the United States at this time.

-- Many of you who are about to get a coronavirus vaccine wanted to know when maximum immunity kicks in. According to the Centers for Disease Control and Prevention (CDC), you’re considered to be fully vaccinated two weeks after the second shot of the two-dose Moderna or Pfizer vaccines, and two weeks after the single-shot Johnson & Johnson vaccine.

-- Another frequently asked question is whether it’s OK to get the coronavirus vaccine at the same time as other vaccines. Just as a precaution, the current recommendation is that the COVID-19 series be administered alone, with at least a two-week interval before and after any other vaccines.

-- Some of you weren’t sure whether the vaccines contained ingredients to which you have known allergies. “I am severely allergic to povidone, which is frequently seen listed as an inactive ingredient in both over-the-counter and prescription medications,” a reader wrote. “Is this a cause of concern with the COVID-19 vaccines?” Polyvinylpyrrolidone, also known as povidone, or PVP, is a water-soluble synthetic polymer that helps keep drugs in suspension. We have reviewed the COVID-19 vaccine ingredients and do not see povidone listed.

-- A reader whose son recovered from Guillain-Barre syndrome (GBS) as a child asked whether the coronavirus vaccine is safe for him an adult. Persons with a history of GBS may receive the COVID-19 vaccine unless they have been previously instructed to avoid vaccination. As this is the case with your son, who has been advised to avoid the flu vaccine, be sure to check with your health care provider for specific recommendations before moving forward with coronavirus vaccination.

We’ll close with a reassurance to those of you who ask that your names not be used in the letters column. We do not publish the names of our correspondents. However, we do love picturing where you’re writing from -- so if you’re willing, feel free to include your city or state in your emails. As always, thank you to our readers who have taken the time to send kind and encouraging words. It really does mean a lot to us.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: A friend from work needs surgery for lung cancer. He was doing breathing exercises, which he said was part of prehab -- something I’ve never heard of. I don’t want to bother him with questions, but am curious: What’s prehab, and why would it be important?

Dear Reader: Prehab is shorthand for prehabilitation, similar to rehab and rehabilitation. It’s based on the idea that patients, by building up strength and stamina before their surgery, may be able to improve their post-surgical recovery.

Prehab first became common with orthopedic surgeries such as hip, knee or shoulder replacement; rotator cuff surgery; joint fusion; and ACL surgery. These are procedures that require sustained physical therapy for the patient to recover full function. The thinking was that the enhanced fitness achieved through a program of prehab could help prepare orthopedic surgical patients for rehab, and thus ease and even speed their recovery process. The concept of prehab gradually began to be adapted to other types of surgeries and procedures, including cancer surgeries.

Some people with non-small cell lung cancer diagnosed at an early stage may be helped by surgery. It’s a complex procedure that can range from cutting out a small portion of the lung to the removal of the entire lung. Unfortunately, not all patients are suitable candidates.

Among the criteria that make a patient eligible is an assessment of the individual’s physical condition, and whether they are physically fit for surgery; this includes having certain levels of heart and lung function. In some cases, these levels can be improved with a program of physical exercise, breathing exercises and other types of therapy. Some lung cancer patients deemed unfit for surgery have, with a targeted program of prehab, been able to improve their heart and lung function enough to go ahead with their procedure.

Prehab has also been shown to improve a lung cancer patient’s recovery following surgery. In a study published in 2019, researchers followed two groups of patients undergoing surgery for non-small cell lung cancer. One group took part in a two-week prehab program. This included performing daily aerobic exercise, resistance training and breathing exercises, as well as following specific nutritional guidelines. They also received counseling and psychological support. The other group of patients had no special preparation prior to surgery. The study participants were evaluated one month after each of their surgeries. The group of patients who had participated in prehab was found to have better heart and lung function than the group that had no prehab.

So far, studies that quantify the benefits of prehab are limited. However hospitals that offer this type of approach say their patients feel supported by the programs. They report that the techniques they learn help them not only through the immediate aftermath of surgery, but into their long-term recovery.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)