There is sometimes some confusion about whether COVID-19 is the same as 'flu. Is it just a type of 'flu? Is it a more virulent strain like the 'flu of 1918 (Spanish flu)? Can't we just treat it in the same way that we treat the 'flu?
There are similarities between COVID-19 and influenza
- They are both respiratory diseases.
- They are both contagious.
- They are both airborne (can be transmitted via tiny particles suspended in the air). Droplet (close contact infection from larger sized particles) or fomite transmission (from surfaces) is also common to both.
- They can both result in pneumonia which complicates the patient's outcome.
- Those infected can be asymptomatic (no symptoms), have mild symptoms, have moderate symptoms, or have severe symptoms. Some patients will die.
- People infected with either COVID-19 or 'flu can transmit the disease while asymptomatic, hence they may never know that they have passed on a disease to others.
- Symptoms of COVID-19 and influenza can be similar, but loss of taste or smell is far more likely to occur with COVID-19 than with 'flu.
CAN COVID-19 be diagnosed by symptoms?
Neither 'flu nor COVID-19 can be diagnosed from the symptoms experienced by the patient, although previously, unless it was clinically necessary, GPs may have diagnosed 'flu based upon sympoms. (That's less likely to happen now with the risk of COVID-19.) A diagnostic test (PCR) is the most accurate way to test for either 'flu or COVID-19, and there's even a est (multiplex assay) that can test for influenza A, influenza B or COVID-19 at one and the same time.
REDUCING RISKS is the same for both diseases
- Hand hygiene
- Cough etiquette (cough into crook of elbow, not into hands)
- Social distancing
- Air filtering/purifying/ventilation
- Mask wearing (ensure no gaps)
- Avoid touching face or adjusting mask
- Quarantine and isolation where required
VIRUS THAT CAUSE COVID-19 vs VIRUSES THAT CAUSE 'FLU
These two diseases are not caused by the same viruses. COVID-19 is not a type of 'flu.
Coronavirus
SARS-CoV-2, the virus which causes COVID-19, is a coronavirus (spherical, with a lipid (fat) layer, and their surface is studded with protein spikes) which is a positive-sense single-stranded RNA virus. It enters human cells primarily by binding to an enzyme called ACE2. Other coronaviruses include that which causes SARS, that which causes MERS, and those which are part of a range of different viruses that cause the common cold.
SARS-CoV-2 is identified as being a strain of the virus that causes SARS, based upon conserved sequences of nucleic acids. This does not mean that SARS-CoV-2 is a mutation of the SARS virus; these two made the jump from bat-reservoir to humans separately.
SARS is considered to be eradicated in terms of human-to-human transmission, primarily because containment measures were very effective. Patients with SARS were most infectious if they were severely ill, and in the second week of their infection (while their symptoms were severe). There were 774 confirmed deaths due to SARS. Now, because the last outbreak of SARS was years ago, it ceased to be a global priority. No effective antiviral treatments currently exist, and work on a vaccine stalled because of lack of funding years ago. However, that early work was pivotal in driving vaccine development for SARS-CoV-2; without that groundwork, we might still be waiting for a COVID-19 vaccine. This highlights just how important it is for funding to be readily available.
This contrasts with how easily SARS-CoV-2 is spread - in particular with the Delta variant being transmissible within as early as 1-2 days of exposure, and while the person is asymptomatic.
MERS is more deadly than SARS-CoV-2, but nowhere near as easily transmitted. Direct or indirect contact with camels is the most likely route for infection; human-to-human transmission can occur, but it requires close contact, and there's no evidence of asymptomatic transmission. There have been 885 confirmed deaths due to MERS. There's no current effective treatment, but several vaccines are in clinical trials. It is not considered a priority risk to the global population.
Influenzavirus
But when we come to influenza, it's caused by negative-sense, single-stranded, segmented RNA viruses that use glycoproteins as their break-and-entry method into cells. There are four types of influenza: influenza A virus (the most virulent - i.e., deadly - human flu virus, and the one that's responsible for human epidemics/pandemics), influenza B virus (slower to mutate and doesn't cause pandemics, but can still cause deaths globally), influenza C (usually only causes mild disease in children), and influenza D (not known to cause infections in humans).
Quadrivalent 'flu vaccines are highly effective in preventing infection by either of the known circulating influenza B virus lineages, and in fact it is possible that the hygiene/containment measures against COVID-19 have actually eliminated one of those two lineages. There still remains the B/Victoria/2/87 lineage, and the current 'flu vaccine remains effective against that.
By far the most dangerous 'flu virus for us is influenza A. The current 'flu vaccine is effective against the circulating strains (H1N1 and H3N2). The 'flu vaccine must be regularly updated with newly emerging seed strains, as influenza A mutates rapidly. If a new and deadlier strain that could be transmitted human-to-human were to emerge - say, of H5N1 - there would be a timelag before it could be identified and a vaccine developed against that specific strain. In that event, the number of deaths would be high.
"Just" the 'flu?
Let's not minimise the effect of the 'flu upon humans. We see annual deaths of seasonal 'flu, mostly among the unvaccinated and the vulnerable, in the order of ~300,000 globally. Better hygiene measures and an end to the "soldier on" attitude when one has 'flu symptoms does see this number go down dramatically, as evidenced by the 2020/2021 'flu season results.
However, when virulent and highly contagious new strains seed in the wild, there arises a pandemic risk. When we see 'flu pandemics, they are not something to be sneezed at (excuse the pun). They have been deadly and catastrophic. We haven't defeated the 'flu, and living with the 'flu means constant vigilance by the CDC to identify new strains, and using those strains as attenuated versions for use in the updated quadrivalent vaccine for the upcoming season.
Without that ongoing work, the world as it is could not continue to function.
When I hear people comparing the 'flu with COVID-19, they are talking about the 'flu as it is now - that is, under strong control, with high immunity levels in the community due to many people having regular 'flu shots, and those shots being regularly updated with the strains out in the wild. Natural immunity to 'flu lineages doesn't last a lifetime, not even for influenza B, and certainly not for influenza A.
We should not trivialise 'flu. New 'flu pandemics are epidemiologically sure to arise, and they will kill and cause chaos.
But at the moment, we're in the COVID-19 pandemic. COVID-19 has Reff of 8 (Delta variant), and that's higher than the Reff of the 'flu strains that have caused pandemics. Thank God we have developed effective vaccines and that vaccine development is continuing. Thank God we've got oral drug treatments already in line for approval. We'll only get on top of this by global vaccination and in addition by making sure that drug treatments are made available. Vaccination is even more important against COVID-19 than it is against 'flu - but we can't do without either.
Discussion welcome.
