Key Facts About The Seasonal Flu Vaccine: What To Know As Winter...

Fall is here, school is back in session, and pumpkin spice is inescapable. For many of us, this changing season means thoughts of cozy blankets, warming recipes, and maybe a trip to go leaf peeping. But for your friendly neighborhood Health and Medicine Editor, it can only mean one thing: flu season is round the corner, and it’s time to talk vaccines.

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Okay, so maybe I don’t get out much. But in the Northern Hemisphere, September is a good time to start thinking about scheduling your seasonal flu shot, so here’s all the info you need.

Key takeaways

The flu virus changes, and different strains circulate each year, so you should get a flu vaccine annually.
Late September/early October is the best time for most people to get their flu vaccine.
Most people will get a flu shot, but nasal spray vaccines may also be a suitable alternative for some people.
Guidance around vaccine eligibility varies, but in the US the recommendation remains that everyone over 6 months of age should get vaccinated.

Why do you need a flu vaccine every year?

The flu is not just one disease; human seasonal flu is caused by influenza A and B viruses, of which there will be several subtypes floating around every year. Add to that the flu virus’s incredible capacity to swap bits of genetic material around, and you end up with a different set of problematic viruses every year.

Lots of research is going into developing a “universal” vaccine that could hit most or even all of these different variants at once; but until we have that, scientists are left to do their best to estimate which flu strains are going to be the most widespread each year, and to develop a shot accordingly.

When is the best time to get a flu vaccine?

Believe it or not, it is possible to get your flu vaccine too early.

Flu season typically begins in October in Northern Hemisphere countries, peaking somewhere between December and February. As a blog post from The College of Physicians of Philadelphia explains, protection from the vaccine starts to wane after just over a month, but the body also needs a couple of weeks to build the best possible antibody response after getting the shot.

That means you need to try and hit the sweet spot where you’ll be protected fully as the season ramps up but will also have protection that lingers long into the New Year.

For most people, that sweet spot hits around the end of September/beginning of October. You should consult with a healthcare provider to see if that is right for you, or if there are other factors that might mean a different schedule is better.

As we know, it’s impossible to predict exactly how a particular flu season is going to pan out. If you don’t get round to making an appointment until later in October, or even after that, it still might not be too late.

What types of flu vaccines are available?

This is going to vary depending on your location and other medical factors that could be at play.

For the majority of adults, flu vaccines are given as a shot into a muscle, usually the upper arm. Last season (2024-25) in the US, all flu vaccines were trivalent, meaning they targeted three groups of influenza A and B viruses. The injectable vaccines are inactivated, and do not contain whole, live flu virus particles.

Many flu vaccines are formulated using eggs, posing a potential risk to those with severe egg allergies. However, research has found that allergic reactions to vaccines are very unlikely. If this affects you, you should speak to a healthcare provider, as alternative egg-free vaccines may be available.

Nasal spray vaccines are also available – for example, in the UK a nasal vaccine is offered to preschoolers and schoolchildren. These are live attenuated vaccines. Nasal spray vaccines are painless and may be better for people who find receiving injections difficult. They also promote an immune response in the tissues of the nose, which is right where the virus normally enters the body.

However, live vaccines are not suitable for everyone, and people with certain medical histories may have to have a flu shot instead. In addition, the Centers for Disease Control and Prevention (CDC) in the US recommends that adults aged 50 and older should have a flu shot rather than the nasal spray.

The committee that advises the CDC on vaccine policy recently issued recommendations for this year’s flu vaccines, including new guidance that only single-dose vaccines that do not contain the preservative thimerosal be used.

Thimerosal has been at the center of controversy because it contains a form of mercury, which some have claimed can build up and cause toxicity within the body. This is not true; thimerosal contains ethylmercury, which does not accumulate in a toxic way like methylmercury does. Despite scientific data demonstrating its safety, antivaccine activists have continued to call for its removal, pushing the false narrative that it is linked to autism.

Because of this controversy, thimerosal has already been removed from the majority of vaccines, though it was still present in some flu vaccine formulations.

Who should get a flu vaccine?

Again, this will vary depending on your location. In the UK, the National Health Service runs a vaccination program targeting those who are considered most vulnerable to severe complications from flu, but the vaccines are also generally available privately at pharmacies to anyone who wishes to pay for one.

In the US, the CDC continues to recommend that everyone aged 6 months or older should get a vaccine every year. Remember, flu vaccines don't just protect you: they can also save the lives of those around you.

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions. 

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.