Before Halloween arrives, health experts want you to remember a simple rhyme: “Flu Before Boo.”
The message is to get your annual flu vaccine by the end of October, giving your body time to build protection before winter. That protection takes about two weeks to develop, so getting vaccinated now helps you prepare before flu spreads more widely.
The CDC generally recommends vaccination in September or October. Halloween is a reminder, however, not a deadline: If you miss it, vaccination later in the season can still help.
Who needs a flu vaccine?
The CDC’s current guidance recommends an annual flu vaccine for nearly everyone 6 months and older, with rare exceptions.
Vaccination is particularly important for people at greater risk of serious illness, including older adults, young children, pregnant people and those with conditions such as asthma, diabetes, heart disease or weakened immune systems.
Some children need two doses at least four weeks apart. Parents should check with their child’s clinician about whether a second dose is needed.
Can the shot give you flu?
No. A flu shot cannot cause influenza. Traditional shots use killed flu viruses or selected parts of the virus that cannot cause infection.
But some people experience soreness, fatigue, headache, muscle aches or a mild fever afterward. Those temporary reactions can feel like the beginning of an illness, but they are not flu caused by the vaccine.
It is also possible to catch flu shortly before vaccination or during the two weeks before protection develops. And because protection is not perfect, some vaccinated people still get flu. Vaccination can nevertheless reduce their risk of severe illness, hospitalization and death.
Several choices, including a new shot
Most people can receive a standard flu shot appropriate for their age and health. A nasal spray, FluMist, is another option for eligible people ages 2 through 49, although it is unsuitable during pregnancy and for people with certain medical conditions.
For adults 65 and older, the CDC prefers three vaccines: Fluzone High-Dose, Fluad and Flublok. These encourage a stronger immune response, which matters because the immune system often becomes less responsive with age. Older adults also face greater risks of hospitalization and death from flu.
This season brings another option: Moderna’s mFlusiva, the first U.S. flu vaccine using messenger RNA, or mRNA, technology. The FDA approved it for adults 50 and older.
How does the new shot work?
All flu vaccines give your immune system a preview of what to recognize and fight.
A traditional shot supplies harmless flu material directly. The new mRNA shot is similar to the COVID-10 shot. Instead of harmless flu — or harmless COVID in that case — it supplies temporary instructions that tell some of your cells to make a harmless identifying piece found on the outside of the flu virus.
Your immune system learns to recognize that piece and prepares defenses for a future encounter with flu. Your cells do not make a whole flu virus, and the shot cannot give you flu.
The technology also allows faster manufacturing, potentially helping vaccine makers respond more quickly when flu strains change.
According to Moderna, a large study found about 27% fewer flu cases among recipients of the new shot compared with a standard-dose flu vaccine.
For adults 65 and older, the FDA granted accelerated approval after studies showed the vaccine produced antibodies expected to help protect against flu. Moderna must now confirm how well it prevents flu illness in that age group.
While the new shot is approved for older adults, it has not replaced the three vaccines currently preferred by the CDC for people 65 and older. Ask your pharmacist or clinician which option fits your age and health.
Why another shot every year?
Flu viruses change, and protection from vaccination fades. Each season’s vaccine is updated to target the strains expected to circulate most widely.
The match is not always exact because viruses can change after vaccine production begins. Even so, vaccination can provide protection and make illness less severe.
You do not need to understand every manufacturing method to choose a vaccine. The practical goal is to get an appropriate vaccine this fall—and give your body time to prepare before winter.