Dear Doctors: I just got the new COVID-19 booster, and the nurse said hardly anyone is getting the updated shot this year. I’m not surprised because after years of headlines, COVID-19 is gone from the news. I’m also hearing it’s getting harder to track. Do you know why? Are people still getting sick?

Dear Reader: It was just after the new year in 2020 that COVID-19 first entered the general conversation. A new respiratory illness, similar in many ways to pneumonia, was causing concern. Highly contagious, and with no effective treatments or vaccine, it soon expanded into a global pandemic. In the United States, we have had more than 99 million confirmed cases of COVID-19 to date, and the disease has caused more than 1 million deaths.

Today, thanks to vaccines, growing herd immunity and the emergence of effective drugs and treatments, the COVID-19 emergency has ended. No longer a pandemic, it is now considered to be endemic. That means a disease is embedded in the population, but it occurs at predictable and manageable levels. And, interestingly, as you have heard, this transition is also making COVID-19 data more difficult to track. Thanks to accurate home tests and milder illness, not all cases get reported. Hospitalizations, which do get reported, have also dropped significantly. In an effort to predict and prepare for local surges of illness, many communities are now tracking the ebb and flow of the COVID-19 virus in wastewater.

At this time, the Centers for Disease Control and Prevention reports that viral activity in wastewater for COVID-19, which has been low nationwide, is beginning to surge. The same goes for ER visits and hospitalizations. A handful of states -- including New Mexico, Arizona, Massachusetts and Minnesota -- are now reporting high viral activity in wastewater. A new variant, known as XEC, has recently emerged as the leading cause of disease, accounting for 45% of new cases. The good news is that a nationwide surge in COVID-19 activity has not been detected. This may be due to the summer surge, which left many people with short-term immunity.

The nurse you spoke with is correct about the low rate of vaccination with the updated COVID-19 shot. Information collected by the CDC shows just 20% of adults older than 18 have received the updated COVID-19 vaccine. That number improves to 44% when narrowed down to adults 65 and older. This is unfortunate because, although not nearly as deadly as at the height of the pandemic, COVID-19 can still cause serious illness and lead to hospitalization.

People who become infected also run the risk of developing long COVID. That’s the collection of symptoms that linger for months, and sometimes years, after initial infection. Long COVID affects between 10% and 30% of people who have had COVID-19, including those with mild illness. The cause is still not understood, and there is no targeted treatment. The good news is, being vaccinated not only helps protect against infection and serious illness, it also reduces the risk of long COVID. Anyone who hasn’t gotten the updated COVID-19 vaccine should please consider doing so.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I’m a 53-year-old woman, and I’ve been athletic all my life. I’m in a soccer league and have a grinding pain in my right knee. I’ve had knee injuries in the past, and now I’m told I might need a partial knee replacement. Why would that be? What does it entail?

Dear Reader: The knee is the largest and most complex joint in the body. It consists of the lower end of the thigh bone, or femur; the upper end of the tibia, or shin bone; and the kneecap, or patella. The knee joint itself is divided into three compartments. The inside part of the knee is known as the medial compartment, the outside forms the lateral compartment and the area between the kneecap and femur is called the patellofemoral compartment.

When the tissues that form the compartments of the knee become damaged or worn out, knee replacement can become an option. This is a surgery in which portions of the knee joint are replaced with artificial components. The primary reason for this type of surgery is osteoarthritis, a condition in which continued wear and tear has eroded the cartilage that cushions the joint and reduces friction. Rheumatoid arthritis, which is an inflammatory condition, and knee injuries can also require a knee replacement.

This type of surgical repair falls into two main categories: total knee replacement and partial knee replacement. In a total knee replacement, also known as arthroplasty, the surfaces of the tibia, femur and patella are all replaced. When damage to the knee joint is limited to just one area of the knee, a partial replacement is possible. Known as a unicompartmental knee replacement, only one of the three compartments of the knee is resurfaced.

In order to know if a knee replacement would be beneficial and which form of the surgery may be required, you would consult with an orthopedic surgeon. They will take a medical history, ask about injuries and pain and evaluate the range of motion, strength and stability of your knee joint. X-rays, and possibly other forms of imaging, are used to visualize the location and extent of damage. You will also be advised of possible complications, which include blood clots, infection, nerve damage, problems with prosthetics and a reduced range of motion.

The surgery itself, which typically takes place under general anesthesia, lasts between one and two hours. The surgeon makes an incision, removes damaged bone and cartilage and replaces it with prosthetic parts. A smooth plastic spacer, which mimics the cushion of cartilage that has been removed, will also be inserted. In most cases, the person returns home the same day.

Recovery from a partial knee replacement takes several months. You will receive a customized recovery plan that includes pain management, wound care, mobility guidelines and exercises. Many patients find working with a physical therapist to be extremely helpful. Patients are often back to a normal routine within six weeks. The lifespan of a partial knee replacement is about 10 years. In some cases, a total replacement may become necessary in the future.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Hello, dear readers, and welcome to our monthly letters column. Flu season in the United States peaks during December, January and February, so please take precautions. We recently wrote about several common respiratory illnesses, including influenza, whooping cough, COVID-19 and pneumonia. We also discussed how to protect those around you when you’re ill. If you missed any of these, or would like a refresher, check out our archives. And now, your letters.

-- In a column about whooping cough, we wrote about the importance of vaccines. These are DTaP and Tdap, each of which protects against whooping cough, diphtheria and tetanus. DTaP is recommended for children and infants under age 7. Tdap, a booster, is for children 7 years and older, adolescents and adults. As a reader pointed out in his letter, it is important for an infant’s caregivers to be current on the Tdap booster. “You could have mentioned that pregnant women should be vaccinated with Tdap to help protect newborns,” he wrote. “And new dads and grandparents who are potential babysitters for a newborn should also have a Tdap booster.” We appreciate the chance to expand on vaccine recommendations. Because whooping cough is a particular danger to infants and young children, everyone who spends time with an infant should be current on whooping cough vaccines and boosters.

-- We recently wrote about the importance of good-quality sleep and shared strategies that some people find helpful. One is the use of sound machines, which can create a soothing environment and mask disruptive noise. We heard from a reader who wondered about safety. “I read that listening to the same sound for very long could be bad for your hearing,” he wrote. “Do you have some information about that?” The primary safety concern when using a sound machine is volume. The repetition of the same sound, when played at a safe volume, does not pose a danger. Although an official standard for volume has not been set, the general consensus is that for infants and children, a sound machine should never exceed 50 decibels. For adults, below 60 decibels is considered optimal. The machines should be located at least 7 feet away from the sleeper.

-- A reader concerned with the effects of an enlarged prostate wondered about a stent as a possible treatment. “As men get older and the prostate enlarges, it causes urinary flow and other problems,” he wrote. “I always wondered why it can't be dealt with by the insertion of a stent at the point of restriction.” A stent is a small tube used to hold open a narrow or unstable anatomical passageway. Although the idea of a stent to prop open the urethra makes sense, in practice, a number of complications can occur. They can be uncomfortable, contribute to incontinence, cause an obstruction and become infected. Prostatic stents are used in specialized circumstances, but at this time, they are not considered a primary treatment.

Thank you, as always, for taking the time to read and respond to these columns. We appreciate your feedback and look forward to hearing from more of you.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)