Season’s Greetings: Welcome to Influenza Season

The air is crisp, the days are shortening, Starbucks is hocking their pumpkin spice creations, and I see people sneezing into their hands everywhere I go. Although we often think of there being only four seasons, many cultures recognise more than just those four. In Bangladesh, there are 6 in total and autumn is broken into shorotkal (early autumn) and hemontokal (late autumn). For public health practitioners, we also acknowledge a special season: Influenza Season.

Public Health measures the calendar year broken into what we call CDC or Morbidity and Mortality Weekly Report (MMWR) weeks. They run Sunday-Saturday and Week 1 begins the first Sunday of each year. Influenza Season (in the Northern Hemisphere) is generally considered to be between Week 40 (around the first week of October) through Week 20 (the end of May).

Unfortunately, just as cold, dry air makes our noses more hospitable to the virus entering our bodies and and poorer weather keeps us indoors, school also begins and large numbers of children spend whole days sneezing on each other and refusing to wash their hands. It’s an annual recipe for disaster.

Because some of terms may be unfamiliar, I have included a glossary at the end of this post.

Is it a cold or the flu?

We often call anything that gives us the sniffles (and even stomach bugs) the flu, but influenza viruses are much more serious than cold viruses and have very different symptoms. The table below from the CDC outlines the differences in symptoms between influenza and “the common cold.”

Influenza usually has a very rapid onset—you feel like you’ve been hit by a truck straight away rather than gradually feeling more and more poorly over a series of days. Fevers, fatigue (tiredness), and aches are common, but shivers are not. Headaches and chest congestion (lots of coughing and feeling like there’s gunk in your lungs) are likely to be influenza, but sneezing, stuffy noses, and sore throats are more likely to be from a cold.

Because both colds and the flu are caused by viruses, you should not take antibiotics to treat them. Antibiotics only work for bacterial infections and taking them to treat a viral infection or seasonal allergies will just cause resistance.

Although a cold may have you feeling poorly for a few days, influenza may require medication (tamiflu), hospitalisation, or could even cause death. Understanding what kind of illness you have can help you better understand how long you’re likely to feel unwell (a few days for a cold vs potentially a few weeks for the flu) and how to treat it.

Why do we worry about influenza?

Influenza is the name for several kinds of viruses which circulate all year, but are more prevalent (common) in the Northern Hemisphere from October through May. Influenza viruses come in three primary groups—A, B, and C. Influenza A affects a wide variety of animals (see the graphic below), Influenza B affects humans and seals, and Influenza C affects humans and pigs.

Of the three types of influenza, A is the one for which we often feel the most concern. Influenza A has the ability to recombine in animal hosts and spread between humans to become epidemics and pandemics. All influenza mutates rapidly because it’s “sloppy” and doesn’t properly check its genetic code when replicating—something we call “antigenic shift.” In contrast to the more gradual “antigenic drift,” which is slower and therefore easier for us to adapt to, antigenic shift happens very quickly and is much more challenging for both scientists and our immune systems to tackle.

In November 1918, soldiers and sailors lucky enough to survive WWI (“The Great War”) were heading back to their homes in Europe, North America, and Asia. Unfortunately, these people who had already suffered so much for so many years were bringing something awful home with them—a strain of influenza which is commonly called Spanish Influenza. Although Spain disputes whether this flu was actually Spanish, no one can deny that it was catastrophic for the world. By the time the pandemic ended, at least 500 million people (roughly a third of the global population) had been infected and an estimated 50 million died.

The flu had been circulating on the battlefields before the end of the war amongst the mud and blood and malnutrition, but the massive exodus of people from the battlefields is what gave the virus the leverage it needed to spread. The particular strain of influenza responsible was more deadly than usual seasonal flu and killed young adults (20-40 years) much more often than would be expected, which made it deadlier than it otherwise might have been.

Scientists are always on the watch for the next pandemic influenza strain and are mindful about the migratory patterns of birds which would carry what we call “highly pathogenic avian influenza.” While we don’t have people pouring out of battlefields across the world anymore, we do have millions of people and birds flying across the world each day and diseases know no borders.

Bird migratory flightpaths via Bird Life International

Calling for backup!

As we’ve discussed before, our immune system is much better at fighting pathogens (germs) when we’ve encountered them before and the large and rapid changes that come from antigenic shift can make influenza so novel (new) that our immune system isn’t prepared to fight them without help. That’s where your annual flu shot enters the scene.

Like the style editors at Vogue predicting next year’s fashions,* immunologists study trends in currently circulating influenza strains and then build the next year’s influenza vaccine to “match” them. They don’t always pick exactly the right strains, but the flu shot isn’t just about preventing cases of infection. The flu is a serious illness and vaccination can help reduce severity, decreasing the number of hospitalisations and deaths each year. Influenza can and does kill thousands of people each year in the US alone, so reducing severity can go a long way to saving lives. Even if the strain match isn’t perfect, it could be the extra leg up your immune system needs to effectively fight the similar strains you’ll encounter.

Keeping ourselves healthy all season

So what can we do to keep ourselves healthy? Thankfully, a lot!

1. Get your seasonal flu vaccine (if you are medically able).

As we’ve discussed here and have have before, the flu is a serious disease and vaccination is a critical component of both controlling its spread in our communities and reducing the number of severe cases. Even if you are young and health (and therefore less likely to die of garden variety seasonal influenza), many of the people around you are not. Children under 5, the elderly, and people with medical complications like asthma or other underlying respiratory diseases are less likely to survive the flu. You can help protect yourself and them by choosing to be vaccinated.

If you are a healthcare worker, your employer may require it or exclude you from work (sometimes for weeks) if you become ill to protect your patients.

2. Wash your hands.

I know this one seems a bit more basic, but it’s worth repeating. Handwashing is very, very important. The world around us is covered in things which long to make us sick and every time we touch a doorknob and then bite our nails or rub our eyes, we invite those bugs into our bodies.

3. Cough and sneeze into your elbow or a tissue.

Similarly, when we cough or sneeze into our hands and then touch things, we are spreading whatever our body was trying to expel. I carry handkerchiefs in the pockets of my dresses and will often try to catch my sneeze inside my cardigan. When my son was small, I began encouraging him to “sneeze in his wing” which was an easy way to help him remember to not broadcast his sniffles to everyone at nursery school.

4. Stay home when you’re unwell.

Although you are able to spread influenza before you are symptomatic (so, before you begin to feel ill), you should stay home when you are unwell. Staying home when you are feeling poorly will help your body recover and will reduce the chances of you making someone else ill by spreading what you have.

I recognise that, especially in the US, paid sick leave is uncommon. If you are a manager or a supervisor in a workplace which does not offer paid leave or does offer it and discourages employees from using it, please use your influence to change those workplace policies. For everyone else, call your local government officials and tell them that your city deserves paid sick leave.

Glossary of terms

Antigenic drift: Gradual changes over time to a viruses genetic code.
Antigenic shift: Rapid changes to a virus’s genetic code. An example of this is the recombination of an avian (bird) flu strain in a pig and was able to spread human-to-human. This was the source of the 2009 H1N1 (“Swine Flu”) Pandemic.
Epidemic: The spread of a disease to a large number of people in a short period of time. An example of this is the 1854 cholera epidemic.
Pandemic: The spread of a disease across the planet in a short period of time. An example of this is the 1918 Spanish Flu Pandemic we explored above.
Recombination: When strains of influenza from multiple hosts (e.g., an avian flu in a porcine host) and undergo genetic changes. See antigenic shift.

*Forever grateful to my stylish friend Milli for cluing me into such an excellent analogy.