The annual flu vaccination is your best shot at staying healthy during respiratory illness season. Respiratory illness season typically starts in October, peaks in the winter, and there is still risk of getting sick through May. The most common respiratory illnesses include influenza, RSV (respiratory syncytial virus), COVID-19, and pneumococcal diseases like pneumonia and middle ear and sinus infections.
Last season, October 2025 through May 2026, was the most severe flu season on record in Colorado, especially for children, and that included 8 pediatric deaths from flu complications.
This year flu hit Colorado early, with positive flu tests and flu-related hospitalizations and one pediatric death already recorded. Currently, vaccination rates across the state are low and very low in our six-county health district. Immunization is important because any of these respiratory diseases can cause serious illness, even in otherwise healthy people, but even a mild case can mean missed school and lost workdays. Respiratory illnesses spread easily through tiny droplets released when people cough, sneeze, and talk, especially when people are in close and closed quarters like we often are once the weather gets cold. It is also possible to get more than one respiratory illness at the same time. Immunization is the first step in building a good defense system to protect ourselves and our families from serious illness.
Vaccines work by introducing a tiny amount of a weakened or killed virus that our body’s immune system uses as instructions to develop antibodies that will be available to fight off that specific virus at a later time when we are exposed to the full disease.
Depending on the vaccine type and individual’s age and immune status, it can take one to four weeks for the immune system to become fully armed against that virus, which is why it is important to get our vaccinations early. However, with vaccines, it is definitely true that it is “better late than never.”
Because vaccines stimulate your immune system to recognize and build protection against a specific disease, you may experience mild, temporary side effects such as a sore arm, fatigue, headache, muscle aches, or a low-grade fever. These reactions are normal and typically go away within a few days. Not everyone experiences side effects, and not having them does not mean the vaccine isn’t working. It is important to remember that the flu vaccine cannot give you a case of the flu.
There are some viruses that remain very stable, so the vaccinations we get as children last basically a lifetime – that is the case with measles, which is why it’s not necessary to get a new measles vaccination if you have had the recommended two-dose series as a child.
However, other viruses, including flu viruses, are constantly changing. The vaccines are updated each year to protect against the strains that are expected to spread during the next season. This is why it is so important to get a flu shot every year – you want to be covered for whichever strains are spreading that may be different from the previous season. It is possible to still get sick from flu even when vaccinated, but typically the symptoms will be much milder. This is for several reasons:
- Each vaccine is designed to protect against the most expected strains for the season and other strains can be circulating that will still make you sick – one of the most important benefits of vaccination is reducing the risk of serious illness and complications.
- Since immunity does take some time to develop it is possible that you could have been exposed to a flu virus before your immunity is fully developed and still get sick shortly after a vaccination, but this does not mean the vaccine gave you the flu.
- It is possible to get more than one respiratory illness at a time so you may have symptoms that are common with flu but not actually have flu.
Many of the symptoms of respiratory illness are similar to the common cold and allergies, including cough, sore throat, headaches, sneezing, runny nose, and congestion. Symptoms such as fever, body aches, difficulty breathing or wheezing, and extreme fatigue accompany flu, COVID-19, RSV, and pneumococcal infections. Children may also experience vomiting and sometimes diarrhea.
It is recommended for everyone six months and older to get a flu shot. Flu and associated respiratory illnesses are especially dangerous for babies, older adults, pregnant women, and anyone with underlying health issues, especially people with heart or lung diseases or who are immune compromised. Your healthcare provider can help you decide which additional vaccines, like COVID-19, RSV, and pneumococcal are appropriate for you and your family based on risk factors. If other vaccinations are recommended, it is also safe and convenient to get them during the same visit.
If you become sick this season, get tested right away and take antiviral medication if prescribed by your healthcare provider. Treatment works best if started within 1-2 days after symptoms begin and helps reduce symptoms, shortens the length of time you are sick, and lowers your risk of developing complications.
Other things you can do to reduce your risk of getting sick, once you are vaccinated, are general healthy habits anytime:
- Wash your hands regularly following the 5 steps: wet, lather, scrub, rinse, dry.
- Regularly clean and sanitize high-touch areas.
- Take steps for cleaner air and more fresh airflow: open windows on nice days, use HEPA air cleaners, and replace your HVAC filters as recommended.
- If you get sick, take precautions to prevent spreading to others: stay home if you can, get tested and seek treatment, wear masks and keep your distance as much as possible, especially from young children, older adults, and people with risk factors for severe illness.
If you are interested in more information about respiratory illness season, expectations for the 2026-2027 season, vaccination recommendations, or how vaccines help prevent serious illness, please visit any of the following articles:
cdc.gov/flu-vaccines-work/benefits/index.html
cdc.gov/flu/season/2026-2027.html
