DEAR DR. ROACH: I am an advocate of flu shots (and other immunizations) to protect both myself and others around me, and I have just had mine for this season. I have a friend, though, who refuses to get flu shots under the assumption that if she allows her body to confront the viruses and deal with them on its own, her immunity will be strengthened naturally. I actually have encountered this philosophy from several different people over the years, and would appreciate it if you could provide a short explanation as to why this is or is not correct. It’d clear up what seems — to me, anyway — to be a fairly common area of confusion. — KW

ANSWER: There is some truth to this theory, in that there are many conditions where if your body successfully fights off the infection, you get long-lasting immunity. However, the situation is more complex than it first appears.

The most important argument against it is that sometimes the body is unable to fight off the infection. There are some conditions where the infection is so overwhelming that people die from it. Tetanus and rabies are examples where the infection is often or usually fatal. Some infections, like polio, may cause serious complications.

There also are infections where the virus constantly changes, so the immunity you got from successfully fighting it off last time doesn’t help. Influenza is the best example of this. Approximately 2,500 Americans die of influenza yearly.

There are other conditions where even if you successfully fight off the infection, your immune system is left weakened for years, making you more susceptible to other infections. Measles is the most important example of this, and it wasn’t understood why for years. Influenza infection also leaves a person vulnerable to bacterial pneumonia.

Immunizations are a way to strengthen the body’s immune system without the full-blown infection and its risks of death, complications and a weakened immune system. Modern vaccines use either weakened live germs or highly purified components of bacteria and viruses to “prime” the immune system — in effect, allowing the body to rapidly defend itself should it ever encounter the fully infectious and virulent organism. The body doesn’t make a distinction between “natural” immunity from surviving an infection and “artificial” immunity from a vaccine.

Finally, as you suggested, by taking a vaccine instead of getting the infection, you don’t expose others. There are many people now with immune system disease, from HIV, autoimmune disease or treatment for cancer and other conditions who could become seriously ill or die from exposure to vaccine-preventable diseases.

DEAR DR. ROACH: My doctor has prescribed progesterone at 100 mg a day to help with mood swings. Is this safe to take, and if so, for how long? Does it increase my risk for cancer? I’m 77, in great shape, do lots of exercise and never had any surgeries, nor took hormone replacement. — A.B.

ANSWER: There are several forms of progesterone, and I am going to assume you are taking natural micronized progesterone, based on your dose. This dose protects against uterine cancer and does not appear to increase risk of breast cancer or heart disease. So, it seems to be safe for long-term use.

However, its benefit for mood swings isn’t completely clear, although I am seeing it used more commonly for this. Please let me know how well it works.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or request an order form of available health newsletters at 628 Virginia Dr., Orlando, FL 32803. Health newsletters may be ordered from www.rbmamall.com.

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