Influenza: Ancient Disease in Modern Times

July 11, 2023

Many folks will get a runny nose or mild sore throat and declare that they have “the flu”. Influenza does indeed cause the symptoms of upper airways viral infection – runny nose, sore throat, coughing. However, it also doubles down with fever, headache and fatigue. If you have ever had real influenza, you will never label a mere cold as such again! Influenza can turn quite serious, causing pneumonia and/or exacerbating pre-existing medical conditions such as asthma or heart issues.  

The disease has been with us a long time. Ancient chroniclers were sadly remiss about including robust immunology data, but the first possible epidemic was in 6000BC China, with the Greek historians describing flu-like illnesses in the 5th Century BC. Epidemics of what was probably influenza occurred across Europe in 1173AD and 1387AD. An epidemic resembling influenza killed most of the population of the Antilles in 1493.  

The first influenza pandemic was recorded in 1510, starting in East Asia and spreading to Africa and Europe. The disease occurred seasonally thereafter, with pandemics every few years. The disease began to be reliably recorded after 1700, as pandemics occurred every 20 to 50 years. The first “bird flu” to hit humans was recognized in 1878.  

The deadliest influenza pandemic was the “Spanish Flu” in 1918-1920, which started in the US and was spread by soldiers travelling to and returning from WW1. It hit in 3 waves and was estimated to have infected as many as half the population of the world. Deaths were in the tens of millions! Since then there was: “Asian Flu” in 1957, killing a million; “Hong Kong Flu”, killing 2 million; and “Swine Flu”, causing hundreds of thousands of deaths. Avian Flu H7N9 emerged in China in 2013 and variants of this have been causing trouble since. Future flu pandemics are considered inevitable.  

There is a wide range in the severity of symptoms. The delay from exposure to presentation is one to four days. People are infective from one day before symptoms till five to seven days after. Children and the immunocompromised may continue to transmit the virus for several weeks. Spread is usually via respiratory droplets, which have a range of about 2m, though it can also occur via the longer ranged aerosol method. The virus can survive for hours on non-porous surfaces. The recommended methods of infection control are respiratory etiquette, hand hygiene, and mask-wearing – although evidence for the effectiveness of the latter is not yet proven with influenza (it is proven with Covid!).  
Antiviral treatments for influenza have existed since Amantidine was approved for use in 1966. Amantidine was only effective against Influenza A, and now not even that, as resistance has developed. Oseltamivir (Tamiflu) is considered first choice therapy these days. It reduces the duration of symptoms by a day or two, and reduces serious complications by 40 to 60 per cent if taken within the first 48 hours. Baloxavir (Xofluza) seems to act faster and be generally more effective at this time, but the picture will change, as resistance is always evolving.

Influenza viruses come in four main variants – A, B, C, and D. Types C and D are more of an animal thing, though they do occasionally cause minor illnesses in humans. Influenza B is more common, but has not yet been associated with a pandemic.

Influenza A is where the action is. This virus has numerous subtypes – classified according to the viral proteins haemagglutinin (H), and Neuraminidase (N). There are 18H and 11N variants. The virologists classify by natural host species, geographical origin, year of isolation and strain number (eg: H1N1/A/Duck/Alberta/35/76).  

As you might expect, the main pillar of controlling the disease is vaccination. With all the sub-strains and the constantly mutating virus, flu vaccine development tends to be based on the educated guesswork done biannually at the WHO. Typical vaccines will be trivalent or quadrivalent, protecting against an H1N1, an H3N2, and one or two IBV strains. Vaccines can be given to anyone more than six months old.  

The efficacy of the vaccine varies a lot from study to study, and is highly dependant on the accuracy of the WHO guesswork. Typically, being vaccinated reduces your risk of catching the illness by 50 per cent, and also gives a 50 per cent reduction in serious complications. Protection arrives within two weeks of the shot, and begins to tail away after six months.  

Dr Julian Martin Chadwick - Internal Medicine Physician
Columbia Asia Hospital - Saigon