What can we expect from the flu season this year? Unfortunately, many experts are predicting an active, and possibly severe, flu season. This projection is based on data from Australia, where the flu season is just wrapping up. Australia was hit early and hard by flu this year: over 300,000 patients had laboratory-confirmed influenza, a record number of cases. Flu outbreaks in the Southern Hemisphere happen during our summers, and they often give us a clue as to what we should expect when the flu lands on our shores in the fall.

Who should get the flu vaccine?

Basically, everybody over the age of 6 months, except for those who have had a life-threatening reaction to a flu shot in the past, should get it. People with egg allergies will likely be able to receive a newer version of the flu vaccine, as described below.

It is especially important to get vaccinated if you are in a high-risk group for developing life-threatening complications from the flu. This includes

• people over age 65
• people who have heart failure and other cardiac conditions, or suffer from asthma, COPD, or other lung diseases
• people who have Parkinson’s disease, multiple sclerosis, strokes, or other neurological problems
• pregnant women and new mothers
• residents of nursing homes and other long-term care facilities
• people who have diabetes, weak immune systems, and chronic liver or kidney disease.

Most people who are hospitalized with influenza have one or more of these risk factors.

When to get the flu vaccine

If you haven’t gotten your flu shot yet, now is the perfect time — that is, around the end of October and the beginning of November. We now think that getting the flu shot very early in the season may be a mistake, as immunity may fade when flu season is at its peak in January and February. Waiting until later may also be a mistake, as flu sometimes peaks earlier than we expect.

What type of vaccine is right for you?

There are several options for flu vaccines. Most are quadrivalent: they protect against two strains of influenza A and two strains of influenza B. There are different processes for growing the viruses to make the flu vaccine: egg-based, cell-based, or recombinant (see below). People allergic to eggs should avoid egg-based vaccines. If you’re older or have chronic illnesses, ask your doctor which vaccine is best for you.

• Egg-based vaccines. The most widely used flu vaccines rely on weakened viruses grown in chicken eggs. This includes a flu shot with inactivated (killed) viruses, and a nasal spray (FluMist) that contains live, but weakened, influenza virus. The nasal spray is mainly used to vaccinate kids and should not be given to patients with high-risk medical conditions. There have been concerns about its effectiveness.
• Cell-based vaccine. A newer quadrivalent vaccine named Flucelvax relies on viruses grown on mammalian kidney cells.
• Recombinant vaccine. A recombinant flu vaccine, Flublok, is also available. It is grown on insect cells, and eggs are not used in its manufacture.
• Vaccines for older and chronically ill people. Many older and chronically ill people have lackluster responses to flu vaccines. Two trivalent vaccines have been engineered to produce better immunity in these patients. The high-dose vaccine (Fluzone) contains higher doses of inactivated virus. The adjuvant vaccine (FLUAD) has an added substance that perks up the immune response. While these vaccines produce better immune responses to influenza, they only cover three strains of influenza versus the four strains in the quadrivalent vaccines.
• Recent data suggest that the cell-based vaccine and the high-dose vaccine may be more effective than the others in preventing emergency room visits and hospitalizations.

Protection with the flu vaccine varies from 30% to 60%, depending on the match between the vaccine and the major circulating flu strains. Because vaccine manufacturing has a lag time of several months, there is always the possibility that the virus-vaccine match may be somewhat off by the time flu season rolls around. But even when the match is not perfect, flu vaccine still reduces the risk of severe illness and death.

What else can you do to protect against flu?

Other measures to protect yourself and others against flu include

• frequently washing your hands or using hand sanitizer
• keeping your hands away from your eyes, nose, and mouth
• staying home from work, school, or church if you have flulike symptoms
• covering your mouth and nose when sneezing and coughing; it’s good for public health (not to mention good manners!)
• if possible, avoiding contact with sick patients until five to seven days after they become ill
• getting both types of the pneumonia vaccine if you are over 65, or if you have an underlying medical condition. This is important because bacterial pneumonia is very common after influenza infection.
• eating well, staying active, and getting a good night’s sleep.

Consider using a humidifier in your home, as well. Flu virus is able to survive longer in dry conditions, which is one of the reasons why flu outbreaks occur mainly in the winter.

Listen to Harvard experts discuss the current flu season a special edition of the Living Better, Living Longer podcast.