Why do we get the flu in winter? Reasons why we are more likely to catch the flu and why flu shots are rarely effective

Why do we get the flu in winter?

Being cold doesn’t literally make you catch a cold, but it certainly seems likely how the coldest season is, as a matter of fact, the 'cold' season.
Why is there a substantial increase in common colds and flus as soon as it gets cold outside?

The flu really does thrive in winter

There’s no doubt that the flu virus somehow thrives in the cold.
As it turns out, the virus is basically designed to jump from person to person when the air is cold and dry. Studies have shown that transmission rates are highest when temperature and humidity are both low. Because cold air naturally holds less water, low humidity levels are typical for winter.
Even when we make our homes comfortably warm, the air stays just as dry unless we use a humidifier.

But why do viruses thrive in cold air?  

Cold air may help the flu virus survive longer outside of a human host, making it easier to linger after a cough or sneeze. And apparently the virus does a better job of circulating in low humidity.
An infected individual exhales virus encased in tiny water droplets, and those droplets evaporate more quickly if the air is dry. If the flu droplet shrinks fast enough, it can become so light that it circulates around in the air instead of falling to the ground.

A few solutions to avoid getting the flu are to always clean your hands if you are hanging out with people whom you don't know or know to be sick and use a humidifier at home or in the office.

Spending more time indoors

You are also more likely to get sick because you’re spending more time inside. That means you’re physically close to other people more often, breathing the same circulated air.
Offices and schools are particularly treacherous. One 2014 study found that a pathogen placed on a single doorknob could essentially infiltrate an entire office building within a matter of hours. Surfaces in the break room were particularly vulnerable to the spread of viruses.

More vulnerable to illness

In addition to making it easier for the flu virus to circulate, cold, dry air leaves your mucus membranes in rough shape. That’s why respiratory illness increase in winter: mucus is supposed to coat your respiratory system to protect it from pathogens, and wintry air dries that beneficial snot right up.

Seasonal changes also cause allergies to flare up as we’re exposed to different kinds of pollens and dander. When your nose is running and your throat is all itchy, your mucus membranes are irritated and vulnerable—which makes it easier for an opportunistic virus to make itself at home.
Persistent allergies can also lead to secondary bacterial infections in your throat or sinuses.

And finally there's also the decreased resilience of our immmune system, because of lack of 'sunshine' vitamin D.

Different types of flu viruses cause lower effectivity of flu vaccines

Unlike almost all other vaccinations, where the effectiveness rate of vaccination is almost 100% , getting a flu shot will not always protect you.
The main reason for this far lower effectivity is that there are many different influenza virus strains.

There are three types of flu viruses: A, B, and C. Type A and B cause the annual influenza epidemics that have up to 20% of the population sniffling, aching, coughing, and running high fevers. Type C also causes flu; however, type C flu symptoms are much less severe.

Type A flu or influenza A viruses are capable of infecting animals, although it is more common for people to suffer the ailments associated with this type of flu. Wild birds commonly act as the hosts for this flu virus.
Type A flu virus is constantly changing and is generally responsible for the large flu epidemics. The influenza A2 virus (and other variants of influenza) is spread by people who are already infected.

Unlike type A flu viruses, type B flu is found only in humans. Type B flu may cause a less severe reaction than type A flu virus, but occasionally, type B flu can still be extremely harmful. Influenza type B viruses are not classified by subtype and do not cause pandemics.

Influenza C viruses are also found in people. They are, however, milder than either type A or B. People generally do not become very ill from the influenza type C viruses. Type C flu viruses do not cause epidemics.

Different strains of the flu virus mutate over time and replace the older strains of the virus.
Because the mutations are somewhat predictable, and also closely monitored, scientists estimate which types and strains of the flu will be the most dominant in a given year and create a vaccine that protect against the strains that are most likely to cause the flu.
Currently flu vaccines mostly protect against 4 influenza viruses: two against Influenza A viruses and two against Influenza B virus.

What about bird flu?

The avian influenza virus causes bird flu. Birds can be infected by influenza A viruses and all of its subtypes. Birds are not capable of carrying either type B or C influenza viruses.
There are three main subtypes of avian flu, including H5, H7, and H9. The subtypes H5 and H7 are the most deadly, while the H9 subtype is less dangerous.
The H5N1 strain has received the most publicity because of its ability to pass from wild birds to poultry and then on to people. While wild birds are commonly immune to the devastating and possibly deadly effects of H5N1, the virus has killed more than half of the people infected with it. The risk of avian flu is generally low in most people because the virus does not typically infect humans. Infections have occurred as a result of contact with infected birds. Spread of this infection from human to human has been reported to be extremely rare.
Most of the illnesses associated with bird flu have been reported in Asian countries among people who have had close contact with farm birds. People are not able to catch the bird flu virus by eating cooked chicken, turkey, or duck as high temperatures kill the virus.

Why was the flu shot less effective this winter?

In normal years immunization reduces the risk of flu illness by 40 to 60% during seasons when most circulating flu viruses are well-matched to the flu vaccine. Older people with weaker immune systems often have a lower protective immune response after flu vaccination compared to younger, healthier people. Therefore, most flu shots used on older people are stronger to make up for that difference.

The flu has been particularly nasty in this winter season of 2017-2018 because apparently strains have been mutating more rapidly than before, which makes it difficult to create an effective vaccine.

The vast majority of influenza hospitalizations were for influenza A type infections, with only 15% for influenza B. And of those, once again, the vast majority was hit by the H3N2 strain.

A reason why this H3N2 strain was not contained by flu vaccine is that this particular virus does not grow very well in chicken eggs, which is where viruses are generally multiplied.
This H3N2 strain has been circulating continuously in humans since 1968 and is therefore, very well adapted to humans as a host. When replicating inside eggs, H3N2 viruses are prone to undergoing adaptive changes that make them better-suited to the egg environment, but less likely to prompt the right response in humans.

A mutation in the H3N2 strain meant most people receiving the egg-grown vaccine didn’t have immunity against H3N2 viruses that circulated last year, leaving the vaccine with only about 30 percent effectiveness in the USA and apparently only 10% effective in Australia.

Because of the difficulties to grow human-adapted influenza viruses in eggs, pharmaceutical companies have turned towards mammalian cells instead to grow viruses.
Cell-based technology may offer the potential for better protection over traditional, egg-based flu vaccines because it results in vaccine viruses that are more similar to flu viruses in circulation.
However, as this type of vaccine is still in the experimental phase, there are no data yet, to actually support this claim.

Should I bother getting the flu shot, then?

Under normal circumstances, getting vaccinated gives a 50% less chance to catch the flu and if you do catch it, the vaccine may reduce the severity of symptoms.
For those who are vulnerable due to being very old or sickly or when you need to take care of sick people, it makes sense to diminish chances to get very sick from the influenza or pass it on towareds vulnerable people. In the past, teachers would also get a shot for free, which may not even be such a bad idea, given the scarcity of replacement teachers.

What other precautions can I take?

To avoid getting the flu, you should always clean your hands if you are hanging out with people whom you don't know or know to be sick and use a humidifier at home or in the office.
Try to be mindful of what you’re touching and who else might have touched it, and practice good hand washing (or use a hand sanitizer when you don't have access to washing facilities) between touching potentially germy surfaces and touching your face or food.
In order to avoid infecting others, try to work from home when sick and use hand sanitizer after touching shared surfaces (especially in the kitchen and bathroom).

In the most northern (and southern) part of the world, the sun rays aren't strong enough in winter to have you create enough vitamin D of your own, so supplementing it in winter is an excellent idea.

What to do when I'm already hit by the flu?

When you already have been hit by the flu, the best advice is to make sure to get in enough fluids: with gingered tea and bone broth being at the top of the favorite remedies.
You can also feel better by taking a hot bath (or shower) or even just use a steam bath for your face.
When using a steam both add a drop of peppermint or eucalyptus oil to clean your airways.
When you suffer from a headache or sinus pain, put a warm compress on your forehead.
Gargle with salt water or go even further by using a so-called neti pot to clean your sinuses with saline water solution.
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