Dear Mayo Clinic: I just turned 65 and had my annual physical. This year, my doctor recommended that I receive a high-dose flu vaccine. Why do I need a high-dose vaccine?

Answer: Influenza is a viral infection that attacks your respiratory system, including your nose, throat and lungs. Influenza, commonly called the flu, is not the same as stomach flu, which is an intestinal infection marked by watery diarrhea, abdominal cramps, nausea or vomiting, and sometimes fever.

For most people, the flu resolves on its own. But sometimes the flu and its complications can be deadly.

People at higher risk of developing flu complications include:

• Children under 5, especially those under 6 months.
• Adults 65 and older.
• Residents of nursing homes and other long-term care facilities.
• Pregnant women and women up to two weeks postpartum.
• People with weakened immune systems.
• Native Americans.
• People who have chronic illnesses, such as asthma, heart disease, kidney disease, liver disease and diabetes.
• People with a body mass index of 40 or higher.

Although the annual flu vaccine isn't 100% effective, it is the best defense against flu. Experts recommend that those 6 months and older get vaccinated for flu. Given your age, that is the likely reason why your health care provider recommended the high-dose vaccine.

High-dose flu vaccines are like other flu vaccines in that they are made up of the flu strains most likely to cause an infection during the upcoming season and they are given by injection. But they are only approved for people 65 and older.

High-dose vaccines include four times as much flu virus antigen — the part of the vaccine that stimulates the immune system — as standard flu vaccines. This can give older people a higher immune system response against flu.

Some older adults may have weaker immune systems, which can lead to them being less protected after a regular flu vaccine. In response to a regular flu shot, older people produce 50% to 75% fewer antibodies than younger adults. These antibodies protect against vaccine antigens.

Studies have found higher antibody levels in older adults who received high-dose flu vaccines than in those who received standard-dose flu vaccines.

In addition, one study found almost 25% fewer cases of influenza in adults 65 and older who took the high-dose vaccine, compared with those who took the standard-dose vaccine.

As with any vaccination, the high-dose flu vaccine has side effects. In a large study comparing standard and high-dose flu vaccines, those who received the high-dose vaccine were more likely to develop side effects the week after getting vaccinated. Side effects included a headache, soreness at the injection site, muscle aches and fatigue. Typically, side effects ease after a few days.

Studies continue to evaluate the outcomes of high-dose flu vaccines. If research finds outcomes to be better than standard flu vaccines, high-dose flu vaccines may eventually become the vaccine of choice for most adults, not just those 65 and older. But for now, it's most important to get vaccinated for flu annually, whether it's a standard or high-dose flu vaccine.

As COVID-19 also remains a threat, consider protecting yourself further by getting vaccinated for COVID-19. Talk with your health care provider about what is right for you. Also, be mindful of the different symptoms you may develop to accurately diagnose whether you may have side effects from a vaccination, flu, COVID-19, or another virus or coronavirus.

—Compiled by Mayo Clinic staff