Living here on the equator, we tend to ignore the annual arrival of the influenza season, which comes with winter in the temperate climates of the northern (December to February) and southern hemispheres (June to August).

Perhaps we think that our year-round sunny, warm weather protects us against contracting this highly contagious respiratory infection.

However, Sanofi Pasteur Global Medical Affairs head Dr Ng Su-Peing has a word of caution for us: “One of the challenges for us in Asia, in the equatorial area, is that flu is all year round.”

The medical doctor based in Singapore adds: “Unfortunately, in Singapore and Malaysia, being right on the equator, you can get flu all year round.

“When the Australians come and visit Singapore and Malaysia, they bring their southern hemisphere flu; when the English come and visit Singapore and Malaysia, they bring their northern hemisphere flu.

“And so, in fact, that makes it harder for doctors to decide when is flu season and when to give vaccinations.”

Dying from complications

The thing about influenza – or the flu, in short – is that it can be quite difficult to differentiate from the common cold.

Both infections commonly cause sneezing, stuffy or running noses, coughs and sore throats.

Other symptoms like fever, body aches and fatigue, are more common and more severe in flu patients, although they also occur in colds.

Both conditions are caused by viruses that attack our respiratory system, although the viruses that cause the cold and the flu respectively are different.

While the flu is caused by the influenza virus, the cold can be the result of infection by over 200 types of viruses, with the rhinovirus responsible for about half of all cold cases.

Usually, those who have caught either condition will recover on their own, with the main difference being that the flu usually affects patients more severely than the cold.

However, even with self-recovery, being sick means time away from work, being unable to fulfil household and family responsibilities, and of course, feeling lousy and miserable.

More troubling is that for certain groups, the flu can prove to have far more serious consequences, including death.

Says consultant respiratory and intensive care physician Dr Felipe Froes: “Community and healthcare workers don’t take flu too seriously because they think influenza is a benign disease that does not cause significant harm and does not require prevention.

“The reasons they think this way is related to two misconceptions: the first misconception, influenza does not kill – in other words, no one dies from the flu – and the second misconception is that influenza only affects the elderly and the very frail.”

It is widely recognised that the elderly, i.e. those above 65 years of age, are the most vulnerable to the dangerous complications of influenza. In this group, the flu can easily develop into pneumonia, which is a serious, and possibly fatal, disease for them.

The head of the Intensive Care Unit of Lisbon’s Hospital Pulido Valente, Portugal, notes that aside from the elderly, other groups vulnerable to influenza’s dangerous complications are young children aged less than three years old, pregnant women, and those with severe and/or chronic conditions.

And it is the complications that are the real killer.

Refering to a statement by the US Centres for Disease Control and Prevention (CDC), Dr Froes says: “We see a lot of influenza, but most people don’t die directly from influenza.

“Only one or two persons in a million with influenza die from influenza – usually viral influenza pneumonia.

“Most people die from complications, like secondary bacterial pneumonia – usually pneumococcus – and chronic diseases like heart failure, diabetes, acute exacerbations of COPD (chronic obstructive pulmonary disease).

“So people usually don’t die from influenza, they die from complications and disease exacerbations.”

He explains that the influenza virus has a direct effect on the respiratory system, destroying the system’s defence mechanisms and paving the way for conditions like bronchitis, sinus infections and pneumonia, as well as triggering asthma and COPD attacks.

The virus can also indirectly affect other organ systems through inflammation, triggering a heart attack, stroke or ischaemic heart disease, or exacerbating diabetes or renal disease.

In addition, Prof Dr Pier Luigi Lopalco notes that influenza pandemics, which affect entire countries, regions, or even the world, tend to occur once every one or two decades.

The last flu pandemic to hit us was in 2009, caused by a new strain of the H1N1 virus, also known as the swine flu virus.

The University of Pisa, Italy, professor of hygiene and preventive medicine says: “We don’t know when a pandemic will come, but we know it will come for sure.”

A wily virus

The reason why we can get the flu over and over again is because the influenza virus is incredibly diverse – different strains can easily combine to form new strains that our immune systems have to continually adapt to and fight against.

Says Sanofi Pasteur Influenza/RSV Global Medical Affairs lead Dr Rosalind Hollingsworth: “Influenza viruses are really sneaky. They are trying to find every possible way they can to evade our immune system and survive.

“And so we find that influenza viruses mutate and change very quickly.”

The two main types of influenza virus that affect humans are type A and type B.

The swine flu virus is a type A virus, which are usually identified as H(number)N(number).

Type B viruses come from two distinct lineages: Yamagata and Victoria, and are identified accordingly.

Due to constantly-evolving nature of influenza viruses, the World Health Organization (WHO) predicts the four most prevalent virus strains that are expected to dominate in the coming year.

An influenza virus seen through an electronic microscope.

This is so that the various pharmaceutical companies that make flu vaccines can customise them according to the predicted strains.

Dr Hollingsworth says: “The WHO makes recommendations based on the most commonly-circulating strains that are identified through their global surveillance programme.

“So, their recommendation in February (for the northern hemisphere, and in September for the southern hemisphere) is based on their best knowledge at that time of the most frequently-circulating influenza strains.”

There is a six-month production period between when the WHO makes their recommendations and when the vaccine is ready for the market. (See p4)

“Unfortunately, in that intervening period, the virus can mutate, so that some of the circulating viruses in the future when the winter season comes, is not a precise match for the vaccine.

“So, that mismatch can, in some years, be problematic,” says Sanofi Pasteur Global Research head Dr Nicholas Jackson.

For example, according to Dr Froes, the prevalent type B virus for the 2018 northern hemisphere winter was predicted to be from the Yamagata lineage, which was included in the trivalent vaccines for the northern hemisphere; however, the dominant type B virus has turned out to be from the Victoria lineage instead.

For 36 years, trivalent vaccines were the main form of flu vaccines, giving protection against three strains of the flu virus – two A strains and one B strain – as predicted biannually by WHO.

Then, in 2014, quadrivalent vaccines were introduced, allowing protection against two A and two B flu virus strains.

Despite the possibility of mismatches between the vaccine and the actual circulating viral strains, Dr Hollingsworth says: “But at the end of the day, the influenza vaccine is always effective, it’s just a question of how effective.”

The CDC, which does annual studies on the effectiveness of that year’s flu vaccine, found that the vaccine’s effectiveness has varied from 10% to 60% from the 2004-05 flu season to 2017-18, with an average effectiveness of 40.6% through the years.

Dr Hollingsworth notes that aside from protecting against the direct effects of the flu, the vaccine also helps to prevent the other complications of flu, especially in vulnerable groups.

She quoted a 2007 Taiwanese study that followed 102,698 people aged 65 and above, of whom 35% received flu vaccinations, for 10 months, which found that those vaccinated had a lower risk of dying from flu complications, compared to those who were not.

These were stroke (65% reduction in risk), renal disease (60%), diabetes (55%), pneumonia (53%), COPD (45%), malignancy (26%) and heart disease (22%).

Overall risk of dying was also lower at 44% among the vaccinated elderly.

In Malaysia, the flu vaccine is not compulsory, but is recommended to be taken annually, especially among those in the high-risk groups.

Dr Ng, Dr Froes, Prof Lopalco, Dr Jackson and Dr Hollingsworth were speaking to the international press during a media trip to visit Sanofi Pasteur’s flu vaccine manufacturing site in Val-de-Reuil, Normandy, France.