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• October: Flu activity often begins to increase.
• December through February: Activity usually peaks, though the exact peak varies each year.
• March through May: Flu can keep circulating, sometimes with a second wave of a different strain.

Chicago’s cold winters push people indoors, where respiratory viruses spread more easily in homes, schools, CTA trains and workplaces. Holiday travel and gatherings add more opportunities for spread. That is why the period right before the holidays is such an important time to be protected.

Because no one can predict exactly when a season will peak, the goal is simple: be protected before flu becomes widespread, and stay protected through the peak months.

Why September and October Are the Best Time to Get a Flu Shot

There are three reasons fall vaccination makes sense for most people.

1. Protection takes about two weeks to build

After your flu shot, your immune system needs roughly two weeks to produce enough antibodies to protect you. Getting vaccinated in September or October means you are protected by the time flu activity begins climbing.

2. Protection fades over time

Immunity from a flu vaccine is strongest in the first few months and gradually declines. This decline appears more noticeable in older adults. Getting vaccinated in July or August, for example, could mean lower protection by late winter, when flu may still be circulating heavily.

3. The vaccine is updated every year

Flu viruses change constantly, so the vaccine is reformulated each season to match the strains experts expect to circulate. Last year’s shot is not designed for this year’s viruses. That is why an annual flu vaccine is recommended for everyone 6 months and older, with rare exceptions.

Is Getting a Flu Shot in August Too Early?

For most adults, especially those 65 and older, July and August are generally considered too early, because protection may wane before the end of the season.

There are some exceptions where earlier vaccination can be reasonable:

• Children who need two doses. Children 6 months through 8 years old who are getting a flu vaccine for the first time, or who have not previously received at least two doses, need two doses at least four weeks apart. Starting earlier helps complete both doses before flu season.
• Pregnant people in the third trimester during July or August. Vaccination at that time can help protect the baby after birth, during the first months of life when infants are too young to be vaccinated.
• People who may not be able to get vaccinated later. If a later visit is unlikely, getting the shot when you can may be better than not getting it at all.

If you fall into any of these groups, talk with your provider about the best timing for you.

Best Time to Get a Flu Shot by Group

Flu Shot Timing for Older Adults

Adults 65 and older are at higher risk of serious flu complications, including pneumonia and hospitalization. Their immune response to vaccines can also be weaker and may fade sooner. For this reason:

• Aim for September or October, not earlier.
• Ask about high-dose, adjuvanted or recombinant flu vaccines, which are preferred for this age group when available.
• Combine the visit with other preventive care, such as reviewing other recommended vaccines or scheduling an annual physical exam.

Flu Shot Timing for Children

Children younger than 5, and especially those under 2, are at higher risk of flu complications. A few timing tips for parents:

• If your child is getting a flu vaccine for the first time and is under 9, plan for two doses. The second dose must come at least four weeks after the first, so start early in the season.
• Children who have had two or more flu vaccine doses in previous seasons usually need only one dose.
• School-age kids can often get a flu shot at the same visit as a sports or school physical. That saves an extra trip and keeps them protected through the school year.

Not sure how many doses your child needs? Bring their vaccine record, and our team can review it with you.

Flu Shot Timing During Pregnancy

Flu can be more severe during pregnancy because of changes in the immune system, heart and lungs. Getting a flu shot during pregnancy:

• Helps protect the pregnant person from serious illness
• Passes antibodies to the baby, helping protect them during the first months of life

A flu shot can be given during any trimester. Pregnant people should get the injectable vaccine, not the nasal spray. If you are pregnant, talk with your obstetric or primary care provider about timing that fits your pregnancy.

Flu Shot Timing If You Have a Chronic Condition

People living with conditions such as asthma, COPD, diabetes, heart disease, kidney disease or weakened immune systems face higher risks if they catch the flu. For these patients, getting vaccinated early in the fall is especially important.

If you are managing a long-term condition with your primary care provider, consider getting your flu shot at your next routine visit. Coordinating care in one place makes it easier to stay current on preventive services.

Can You Get a Flu Shot and a COVID Vaccine at the Same Time?

Yes. CDC guidance allows flu and COVID-19 vaccines to be given at the same visit, typically in different arms. Some people prefer to space them out to reduce the chance of feeling achy from both at once, but there is no requirement to wait between them. Your provider can help you decide what works best for you, and you can also ask whether other vaccines are due.

How Effective Is the Flu Shot This Year?

Flu vaccine effectiveness changes every season. It depends on how well the vaccine strains match the viruses circulating, the age and health of the person vaccinated, and other factors. In seasons with a good match, vaccination has been associated with substantially lower risk of needing medical care for flu.

Even in a season where the match is not perfect, the flu shot can still:

• Reduce the severity of illness if you do get the flu
• Lower the risk of hospitalization and serious complications
• Help protect people around you who are more vulnerable

The CDC publishes interim vaccine effectiveness estimates partway through each season. Any claim of an exact percentage before those data are available should be treated with caution.

What Happens If You Get Your Flu Shot Late?

Missing the September–October window is common. Life gets busy, and many people do not think about vaccination until they hear about flu cases at work or school. The good news is that vaccination is still recommended as long as flu viruses are circulating, which often extends into spring.

A late flu shot still gives you protection for the remainder of the season. If you are wondering whether it is worth it now, read our guide: Is it too late to get a flu shot?

What to Expect After Your Flu Shot

Most people feel fine after vaccination or have mild reactions such as a sore arm, low-grade fever, headache or tiredness for a day or two. These reactions are signs your immune system is responding. For a full breakdown, see flu shot side effects: what’s normal and how long they last.

Seek emergency care right away for signs of a severe allergic reaction, such as difficulty breathing, swelling of the face or throat, hives or a fast heartbeat.

A Simple Plan for This Flu Season

1. Mark your calendar for September or October. Pair it with another errand or appointment so it does not get pushed back.
2. Check your family’s needs. Do any children need two doses? Is anyone 65 or older who should get a preferred vaccine type?
3. Bring your insurance information. Many plans cover the flu vaccine as preventive care. Confirm your coverage with your plan or our front desk.
4. Plan a light day afterward if you tend to feel achy. Most people do not need to, but it can help if you have had reactions before.
5. If you miss the window, get vaccinated anyway. Late is better than never during an active season.

Get Your Flu Shot at Sunny Side Medical Center

Sunny Side Medical Center provides flu shots and other vaccinations for children, teens and adults at 3228 W. North Ave. in Chicago. Our clinic is convenient for families in Logan Square, Hermosa, Humboldt Park, Avondale, West Town and nearby neighborhoods.

During your visit, our team can:

• Review your vaccine history and recommend the right flu vaccine for your age and health
• Check whether your child needs one or two doses this season
• Coordinate your flu shot with a physical, chronic care visit or other preventive services

We welcome in-network and out-of-network insurance as well as self-pay patients. Coverage varies by plan, so please contact us to confirm.

Hours: Monday–Friday 9:00 AM–5:00 PM, Saturday 9:00 AM–1:00 PM.

Ready to get protected before flu season peaks? Book an appointment or call 773-292-9660.

Frequently Asked Questions About When To Get Flu Shot

When is the best time to get a flu shot?

For most people, September or October. This timing allows about two weeks for protection to build before flu activity usually rises.

Is August too early for a flu shot?

For most adults, especially those 65 and older, July and August are considered too early because protection may fade before the season ends. Some children and pregnant people in the third trimester may benefit from earlier vaccination.

How long does a flu shot last?

Protection is strongest in the first few months and gradually declines. One shot is intended to cover a single flu season, which is why it is recommended every year.

Can I get a flu shot in December or January?

Yes. Vaccination is recommended as long as flu viruses are circulating, which often continues into spring.

Do I need a flu shot every year?

Yes. Flu viruses change, the vaccine is updated each season and immunity declines over time.

Can I get my flu shot and COVID vaccine together?

Yes, they can be given at the same visit. Talk with your provider if you prefer to space them out.

How long after a flu shot am I protected?

About two weeks after vaccination.

Related guides: flu shot side effects · is it too late to get a flu shot