SEASONAL FLU | WILL COVID-19 BECOME AN ENDEMIC DISEASE?

The novel coronavirus causing COVID-19, SARS-CoV-2, was discovered in Wuhan, China. It started its course in December 2019. From the track record of coronaviruses, there is a good chance the novel coronavirus will not go away just yet and maybe a regular occurrence like the seasonal flu.

The world has witnessed several health crises as a result of zoonotic (animal-originated) viruses. This is the situation with influenza that created the swine, bird, and seasonal flu outbreaks in recent history.

Seasonal flu alone is estimated to bring about three to five million cases of severe illness, and 290,000 to 650,000 respiratory deaths annually.

Speculations behind the seasonal nature of influenza outbreaks persist. One of such is that people are mostly indoors and in close proximity during the cold season. Consequently, this promotes the transmission of infection-causing organisms from person to person.

According to WHO evidence so far, ‘the COVID-19 virus can be transmitted in all areas, including areas with hot and humid weather’. This is a striking feature. For the most part, however, SARS-CoV-2 has expressed its virulence in cooler, drier regions such as Italy, Spain, and Switzerland.

seasonal flu

What exactly does it mean for a virus to be seasonal and/or endemic?

For pathogens to become endemic, invariably means they are regularly found among particular people or in a certain area. In other words, they are continuously, constantly circulating and in terms of seasonality, will peak during particular seasons. Some parasites, such as the malaria parasite (caused by a plasmodium), circulate all year round in Africa.

Others, such as influenza, cause more infections in wintertime than late spring and summer. The same may be said for the novel coronavirus as with other respiratory viruses. Other endemic diseases include measles, chickenpox, the common cold.

Even with an effective vaccine, SARS-CoV-2 will likely mutate into several strains as seen with the flu. This means regular shots for different strains. Currently, people commonly get infected by four out of seven known human coronaviruses that are highly seasonal – 229E, NL63, OC43, and HKU1.

The other three are the Severe Acute Respiratory Syndrome Coronavirus (1), Middle East Respiratory Syndrome Coronavirus, and Severe Acute Respiratory Syndrome Coronavirus 2; SARS-CoV or SARS-CoV-1, MERS-CoV and SARS-CoV-2 respectively.

What’s the similarity between the human coronaviruses – SARS-CoV-2, SARS-CoV, and MERS-CoV?

These viruses are responsible for viral respiratory infections in humans.

Sometimes, coronaviruses that infect animals can evolve and make humans sick thus becoming a new human coronavirus. Three recent examples of this are SARS-CoV-2 (previously 2019-nCoV), SARS-CoV, and MERS-CoV.

Reproductive Number (R0)

The R0 (pronounced R-naught), is a carefully worked-out number which is a measure of how contagious and reproductive an infectious disease is. This simply represents the average number of people that will be infected by a contagious person in a particular community.

Presently, the World Health Organisation puts the R0 of SARS-CoV-2 at 2 to 2.5

The R0 of SARS-CoV is estimated between 2 and 4, which invariably means just like COVID-19, it is highly contagious.

R0 of MERS is lower than one, this means unlike others it is a mildly contagious disease.

Confirmed cases

According to the CDC timeline, as of April 2020, the global number of confirmed COVID-19 cases was more than 1,290,000 with over 76,000 deaths.

Severe acute respiratory syndrome (SARS) coronavirus was first isolated in November 2002 following an outbreak in the Guangdong province of southern China. Between its emergence in 2002 and May 2014, when the last case was reported, roughly, 8,098 people were infected and 774 of them died as a result.

The Middle East Respiratory Syndrome (MERS) or camel flu was first identified in Saudi Arabia in 2012. It has since reached an endemic stage.

Currently, there are roughly 2,521 confirmed cases of MERS with resultant death of about 866 globally.

Symptoms

Characteristically, symptoms of COVID-19 overlap with those associated with commons colds, allergies, the flu, and other diseases like malaria. These illnesses are caused by different parasites and are all endemic but their peculiarity makes it hard to tell them apart.

WHO suggests that approximately one out of every six infected people will become seriously ill, develop difficulty in breathing and may need a ventilator to survive.

Technically, symptoms of SARS are flu-like, such as fever, malaise, myalgia, headache, diarrhea, and rigor like shivering.

Like COVID-19, MERS could also hide in mild cases and show no symptoms, mild respiratory symptoms, or severe acute respiratory disease and death. Similarly, fever, cough, and shortness of breath are common symptoms. It also gets severe sometimes and will require mechanical ventilation.

Will COVID-19 be endemic like the seasonal flu?

Seasonal flu is endemic or at least people, regions have had previous exposure. Since COVID-19 is infecting people for the first time, a lot of persons do not have what it takes to fight off the infection, not even herd immunity. It is also more contagious.

The scientific community is hopeful that a vaccine will be ready in the next coming months. In comparison, cold symptoms are much milder than flu symptoms, malaria symptoms seem a bit of a combination of the later while the chief amongst them is the novel coronavirus which is capable of causing a more serious complication such as pneumonia.

This can make it tricky to diagnose coronavirus disease on the spot without a test.

But then, just like regular flu, COVID-19 infection, reinfection, testing, and diagnoses would likely become a norm. Personally, I haven’t been tested for coronavirus, nonetheless, without a serology test, there’s absolutely no way to tell if one has contracted the virus or have antibodies. Chances are, as a health worker I have been exposed.

How do environmental factors influence seasonal flu and coronaviruses?

A change in temperature affects other environmental factors such as the amount of water vapor present in the air. It’s not so much that drying out the host deactivates the virus. Rather, if a viral droplet floats around on a moist surface, its probably easier to pick up.

On the contrary, once it is dried and the droplet becomes dormant, technically, it forms a shell. This is much harder to cause the virus to hatch and infect the host.

Unarguably, UV is mutagenic, which invariably means it could damage genetic materials. So, why don’t doctors just radiate people to get rid of the virus? Sadly, individual viruses are so small, so much so that it’ll take a lethal dose of UV to inactivate all of them in a droplet.

It’s not unknown that 1 to 3 hours exposures would reduce the amount of virus tenfold (i.e. from 1,000 particles to 100); seemingly, it would merely take four times as long to reduce 1,000 viral particles to less than 1. This inactivation explains why there’s a reduced likelihood to be infected in temperate regions of the world.

Recently, a scientific paper observed 100 Chinese cities with more than 40 cases of COVID-19 and concluded that the higher the temperature and humidity, the lower the rate of transmission.

Aside from the external conditions, other reasons for a reduction in cases stem from the fact that virus transmission on a seasonal basis is centered on people’s behavior. Behavioral changes through the seasons are instinctual. During cold weather, people tend to feel cozy in crowded areas.

On the flip side, during hot periods, people would most likely feel at home in a well-ventilated environment.

So, how do all these apply to COVID-19?

Warmer temperatures could delay the peak of this pandemic into the late spring and summer. This would mean that the transmission would diminish, but its rather hard to know how far this would go with COVID-19.

However, it is worth pointing out that when its summer in the Northern Hemisphere, its winter in the Southern Hemisphere so as influenza infections are low during one’s summer, others in their winter are taking the hardest hit. For what it’s worth, we can only try to be proactive and adjust to living with this health challenge.

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