Invisible flu: the hidden danger that’s putting older adults at risk

Home stories Invisible flu: the hidden danger that’s putting older adults at risk

Invisible flu: the hidden danger that’s putting older adults at risk

People normally know when they have the flu: the unmistakable fever, aches and pains leave them drained.

Dr. Daniel EorsiFrom time to time, however, people can catch the flu without even knowing it. With ‘invisible flu’ (or ‘asymptomatic flu’ if you want the medical term), they show no signs and feel no symptoms – despite still carrying and unwittingly spreading the virus. In addition to that, people may be able to spread the flu without even coughing or sneezing according to a recent study(1).

This basically means people who seem well could spread the flu simply by breathing.

We asked Dr Eörsi Dániel to explain why some people experience no symptoms with the flu, and what that means as we get older. Find out what the GP had to say:

What is ‘invisible flu’?

Invisible flu is when someone catches the flu but shows no apparent symptoms. They may, at the very most, have a little muscle pain, which they would probably put down to training or some other activity the day before.

Someone with invisible flu would simply carry on as normal.

Why do some people have no symptoms with the flu?

Sometimes a person’s immune system can destroy the flu before they show any symptoms.

The virus still reaches the mucous membrane that lines the inside of their nose, mouth or wherever the virus enters their body, but their immune system kills most of it before it travels any further.

A small amount may reach their bloodstream. Here, their immune system is quick enough to kill it before it multiplies enough to produce symptoms.

Why is their immune system able to react so quickly?

With invisible flu, the person has encountered that specific strain of the flu before. Their immune system knows which specific tool – which antibody – can combat it.

So, when they catch the virus, their immune system quickly recognises it and produces enough copies of the antibody to destroy it before it causes any harm.

Can people with invisible flu spread the virus?

Yes. There is a short period of one to two days between when they catch the flu and when they may be able to spread it. We call this the incubation period, and it is something that everyone who catches the flu experiences.

Once the incubation period has passed, they may be contagious for around two days. During this period, they are at risk of spreading the virus. This period, however, is likely to be shorter than if they experienced symptoms with the flu.

It’s difficult to tell exactly when they acquired the virus, so it is difficult to tell when they may be contagious and able to spread it.

How many people with the flu don’t know they have it?

From my experience and from what research has found, approximately 30 to 50% of flu cases are invisible, depending on the flu strain(2).

As an older person, am I likely to have symptoms if I catch the flu?

Yes. There are two groups of people more likely to have symptoms with the flu: healthy younger adults and older adults, particularly those who have underlying illnesses.

This doesn’t mean middle-aged people don’t catch the flu, simply that incidences of symptomatic flu are not as high in this age group.

Why are younger and older adults more likely to have symptoms?

For healthy younger adults, they are less likely to have encountered a specific strain of the flu before during their shorter lifetimes. When they do catch the unfamiliar flu strain, their immune system reacts strongly to the new virus, and they experience the classic symptoms – a fever along with aches and pains.

For an older person, there are two reasons why they are more likely to experience symptoms with the flu. Firstly, their immune system doesn’t work as efficiently as when they were younger and so can’t kill the virus so quickly.

Secondly, they are more likely to have an underlying chronic disease that is stressing their immune system. When an older person with a stressed immune system catches the flu, their immune system has a strong reaction, just as if it’s an unfamiliar strain – whether it is or not.

This strong reaction can happen for any older person with any chronic disease, not just a chronic respiratory disease.

What final message would you like to share?

Anyone can catch the flu, and anyone can spread the flu – even people with no symptoms.

Everybody in the risk groups – which includes older adults and people with chronic diseases – should protect themselves. After all, it’s not always possible to tell if someone has the flu.



Leave a comment