Dear Doctors: I went to our local pharmacy to get a flu shot for myself and also for my dad. It turns out that because he is 68 years old, he didn’t get the same vaccine as me. They gave him something called “fluad quadrivalent.” How is that different from the regular flu vaccine? Why did he need it?

Dear Reader: First, we want to thank you for taking an important step in safeguarding your health and that of your father. Flu season in the United States started early this year, and it is turning out to be particularly severe. It has resulted not only in widespread illness, but also in high rates of hospitalization. That makes getting vaccinated particularly important.

Due to age-related changes to the immune system, older adults are at increased risk of developing potentially life-threatening complications from a case of the flu. According to data collected by the Centers for Disease Control and Prevention in recent years, well over half of hospitalizations due to the flu, and up to 85% of flu-related deaths, have occurred in adults 65 and older. People of all ages who are living with underlying conditions such as diabetes, asthma, lung disease and heart disease are also at increased risk.

The good news is that this year’s flu vaccine is proving to be effective at reducing the severity of disease and decreasing the risk of hospitalization. By getting vaccinated, you and your dad are protecting yourselves, as well as the people around you.

To understand the difference between the shots you and your father received, we should first define a few terms. All flu vaccines contain something called an antigen. That’s a molecular structure found on the surface of viruses, including the influenza virus. When a virus infects the body, the antigens it contains act as an alarm bell. Their presence triggers the immune system to produce specialized proteins known as antibodies, which attack the invaders.

Flu vaccines work by teaching your immune system to recognize specific antigens. This primes the immune system to be ready with a strong protective response. Although your father got a different shot than the one you received, he did not get a different vaccine. Rather, he was given what is known as a high-dose flu vaccine. That’s a shot that contains the same antigens as the regular flu vaccine but is specially formulated to elicit a stronger immune response. At this time, several types of high-dose flu vaccines are approved for use in the U.S. Each one is formulated in a slightly different way, but all have the same effect -- that is, to rev up immune response.

The fluad quadrivalent shot that your father received contains something called an adjuvant. That’s an added compound that causes a markedly stronger immune response. Another high-dose flu shot, known as Fluzone High-Dose quadrivalent, achieves the same result by upping the quantity of antigens contained in the vaccine.

As with all flu shots, side effects can include soreness or swelling at the site of the injection, fever, muscle aches, headache or nausea. To locate a high-dose flu shot near you, visit vaccines.gov/find-vaccines.

(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 Doctors: Why don’t we hear more about cryoablation as a treatment for prostate cancer? It appears to be much easier than major surgery, so it seems like it would be a good option. What does the procedure entail? I am also interested in knowing about the advantages and disadvantages.

Dear Reader: Prostate cancer is the second-most-common type of cancer in men. Only skin cancers occur more often. This type of cancer arises in the prostate gland, which is about the size and shape of a walnut and is located beneath the bladder.

Because the prostate sits amid a complex network of nerves and structures that contribute to both sexual and urinary function, removing tumors in this type of cancer can be challenging. Depending on size and specific location of the cancer and whether it has spread, prostate cancer treatment can result in urinary incontinence and loss of sexual function.

Therapies may consist of one or more approaches, including surgery, radiation, chemotherapy, hormone therapy or immunotherapy. Cryoablation, also known as cryotherapy, can also be an option in certain cases. This is a procedure in which abnormal tissues are subjected to extremely cold temperatures, which destroys the cells.

Cryotherapy is performed under either regional or general anesthesia. It may be an outpatient procedure, or it can sometimes require an overnight hospital stay. Guided by ultrasound imagery, the physician inserts thin, hollow needles, known as cryoprobes, into a specific region of the prostate gland. The cryoprobes infuse freezing gas into the cells of the prostate gland, which kills them.

There are two forms of cryotherapy for prostate cancer. One type, known as whole-prostate cryotherapy, treats the entire gland. This kills both the cancer cells and the healthy tissues. Freezing the tissues of the prostate gland often damages the nearby nerves that control erections. As a result, erectile dysfunction occurs more often after whole-prostate cryotherapy than when the gland is surgically removed.

The other type of cryotherapy, known as focal cryotherapy, targets only the cancer cells. This allows less of the healthy tissue in the prostate to be destroyed. With focal cryotherapy, the risk of the loss of sexual function is minimized, but not eliminated. This approach is typically reserved for cancers that are small, well-defined and have not spread.

In both types of cryotherapy, a catheter filled with warm saltwater is used to protect the urethra. This is the tube that empties the bladder. The catheter is left in place for several weeks after the surgery, which ensures that the patient can empty his bladder as he recovers.

You are correct that cryotherapy is less invasive than surgery. It is also less painful and has a faster recovery period. However, it is not suitable for all patients. Factors such as the size, location and typing of the patient’s cancer, as well as the size of their prostate, play a role in whether cryotherapy can be an option. It is also unclear at this time if the long-term survival rates of this approach match those of either radiation or surgery.

(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 Doctors: I have read that older adults may not get enough vitamin D in winter. My father-in-law is 73 years old. He’s from Florida, but he’s spending a year with us here in Maine. He can’t be outdoors all the time like he is at home. How important is vitamin D? How do we know if he’s getting enough?

Dear Reader: Your question keys right into why vitamin D is often referred to as the “sunshine vitamin.” It’s a nutrient essential to human health and well-being and is produced by the body in response to exposure to sunlight. Vitamin D helps the body absorb calcium and maintain proper blood levels of both calcium and phosphorus. These functions are critical to the growth and maintenance of healthy teeth and bones. Newer research shows the vitamin has an anti-inflammatory effect, helps the body fight infection and can reduce cancer cell growth in some situations. Vitamin D receptors are found in tissues throughout the body and in several major organs. This suggests additional roles for the nutrient that have not yet been identified.

How much vitamin D someone needs depends on their age. Children, teens and adults up to the age of 70 are advised to get 600 international units, or IU, per day. Absorption becomes less efficient as we age, so older adults, like your father-in-law, are advised to get 800 IU per day. For infants up to 12 months old, the recommendation is 400 IU of vitamin D per day. While the nutrient is found in some foods, such as fatty fish, beef liver, egg yolks, cheeses and some mushrooms, most of us don’t eat enough of these to fulfill our daily requirement. To compensate, a range of commonly consumed prepared foods are fortified with the nutrient. These include dairy products, many breakfast cereals and some brands of prepared orange juice.

And then, of course, there’s sunshine. When the ultraviolet rays in sunlight hit the surface of the skin, they trigger a complex chemical reaction. With an assist from the kidneys, liver and other cellular structures, our bodies manufacture vitamin D. For those with light skin, 15 to 30 minutes of full sunlight on bare arms, legs or torso at least two or three times per week will do the trick. Melanin offers a protective effect, so people with darker skin need longer exposure. People with any kind of history or risk of skin cancer should rely on diet and supplements to get their daily allowance.

It’s important to note that several factors can interfere with natural vitamin D production. Clothing and sunscreen either partially or completely block UV light, which hinders or prevents vitamin D formation. In northern latitudes like your own, with shorter days, weaker sunlight and bad weather that keeps people indoors, getting enough vitamin D naturally can become a challenge. Your father-in-law can learn his vitamin D status with a simple blood test. If it’s low, his health care provider will offer guidance on supplementation. These can include fortified foods, vitamins or, in cases of serious deficit, vitamin D injections.

(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.)