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Mythbuster: ‘Covid-19 is just like seasonal flu’

Woman sneezing.


As the Covid-19 pandemic emerges, comparisons have been made between the new coronavirus and seasonal flu. With the help of the advice from the World Health Organisation (WHO) and other scientific resources, science journalist Helen Quinn has separated facts from fiction, in our Covid-19 v seasonal flu guide for practice nurses.

As the Covid-19 pandemic emerges, comparisons have been made between the new coronavirus and seasonal flu. With the help of the advice from the World Health Organisation (WHO) and other scientific resources, science journalist Helen Quinn has separated facts from fiction, in our Covid-19 v seasonal flu guide for practice nurses.

Novel coronavirus disease (Covid-19) is a highly infectious disease which has caused over 67 000 deaths as of 7 April, since it came to light in China late last year. Like seasonal flu, it is a respiratory disease affecting the upper airways, but what are the main similarities and differences between Covid-19 and seasonal flu?

What is Covid-19?

Covid-19 is a new, highly infectious illness that can affect the lungs and airways.  It is caused by a virus called a coronavirus. 

There are several well-known coronaviruses that we are exposed to regularly and have been circulating in the human population for centuries. These viruses cause common colds.

Covid-19 is from the same family of viruses as the common cold viruses, but this family also includes two other more deadly coronaviruses known as MERS and SARS. Covid-19 is a new member of the family and spreads more easily than MERS and SARS.

Flu is a much older virus than Covid-19. It is caused by the Influenza A or Influenza B virus, a different type of virus from a coronavirus.  

How similar are the symptoms of Covid-19 and influenza?

Both Covid-19 and influenza have very similar symptoms. A patient presenting with Covid-19 might look very similar to someone showing signs of flu.

Both illnesses cause respiratory disease, but in Covid-19 infections, the range of symptoms are more severe, with 15% of cases requiring oxygen and 5% requiring ventilation.

Covid-19 symptoms are usually seen five days after infection,  approximately twice as long as for flu. The maximum incubation period of Covid-19 defines the period required for isolation, currently thought to be 14 days.

Some of the most common symptoms of Covid-19 are fever, a new, continuous cough, and difficulty breathing. A sore throat, fatigue, aches, and pains are also commonly accepted symptoms of Covid-19. A loss of taste and smell has also been reported in some cases but is not currently recognised by Public Health England (PHE).   

Covid-19 can also cause pneumonia, kidney failure, and in the most severe cases, death.

How are the viruses transmitted?

Both viruses are transmitted in the same way, via droplets from the nose or mouth produced when a person coughs or exhales. The droplets can also land on surfaces, and people can catch Covid-19 from touching these surfaces. As a result, public health measures to prevent transmission of either disease are very similar.

PHE suggests that wearing the correct PPE and regular hand washing remain the most important preventative measures for health care workers to avoid infection and transmission of Covid-19.  

Who is most at risk from each virus?

Flu is a risk for children, pregnant women, the elderly, and those underlying health conditions or reduced immunity levels.

The Covid-19 virus is currently thought to pose the most risk for people over the age of 60 and those with underlying health conditions such as cardiovascular disease, diabetes, chronic respiratory disease, and cancer.

Current estimates of the hospitalisation rates for Covid-19 suggest 2% of those infected who are under 50 will need to be hospitalised. This rises to 44% in the over 80s and is equivalent to an average of 8% hospitalisation rate across all age ranges.

How do mortality rates compare?

Although exact mortality rates for Covid-19 will take some time to be fully recorded and understood, they appear to be higher than for seasonal flu.

The current reported mortality ratio for Covid-19, which is taken from the number of reported deaths and the number of reported infections, is between 3-4%. For hospitalised people, mortality rates average 12%, from 4% in the under 50s and to 20% of over 80s.

For those who require invasive ventilation, mortality rates average 50% across all ages.

Influenza has a mortality rate of below 0.1%. Roughly one billion people catch flu every year, and it is estimated that between 290 000 and 650 000 of those who get the illness will die.  

Which illness spreads faster?

Seasonal flu spreads faster than Covid-19 because of the shorter time between successive cases and also because patients with influenza are infectious before their symptoms appear, so they can unknowingly pass on the illness.

It is believed patients who have been infected with Covid-19 can be infectious before the onset of symptoms. Research published on 1 April by the US Department of Health and Human Services based on work from scientists in Hong Kong suggests there may be some evidence emerging that Covid-19 can be transmitted before the onset of symptoms. The World Health Organization on 2 April also stated: ‘Transmission from a pre-symptomatic case can occur before symptom onset.’

Do children transmit both viruses?

It is currently unclear as to the role children play in the transmission of Covid-19. Children are important drivers of seasonal flu transmission, as schools go back after summer flu rates increase within the community.

With Covid-19, children are generally less affected than adults, and preliminary scientific research suggests that adults may infect children.  

What about immunity?

Immunity for seasonal flu is very short-lived. Once a patient has had flu, they may have protection from that particular infection for a few months. However, there are many different strains of the virus, and it is not uncommon for a person to catch more than one strain of flu in a short space of time.

There is a lot to be learnt about the Covid-19 coronavirus. As a new virus, the body will most likely generate a strong antibody response to the illness if a patient survives the initial infection. Scientists believe that immunity will last at least three months, but probably much longer because Covid-19 is such a new virus.

What treatments are available for each disease?

There are currently no approved antiviral drugs or vaccines to treat or prevent Covid-19. Coronavirus patients with mild symptoms are advised to remain at home and take paracetamol to reduce pain or fever, as well as taking on fluids to avoid dehydration.

Flu, however, can be treated with prescription medicines, which are most effective when taken with a few days of the symptoms starting.

What about vaccines?

There is no vaccine available for Covid-19. It is expected that a newly developed vaccine will be available within 18-24 months. Human trials for a Covid-19 vaccine began just 63 days after the RNA code of the new disease was first made available, making it the fastest time for a vaccine to go from the lab into human trials.

Flu vaccines are widely available and are offered annually to at-risk groups of the population. Seasonal flu is still around in the community, and this year with the addition of Covid-19, it is even more critical that at-risk groups have the flu vaccine to prevent unnecessary hospital admissions for influenza when the NHS is already under immense strain.  

Summary: 

·       Covid-19 and flu share some similar symptoms. Flu symptoms usually present in a shorter time.

·       Covid-19 is more likely to cause severe illness or death.

·       Both viruses can be caught from others who have the illnesses. The viruses spread via droplets from the nose or mouth produced when a person coughs or exhales.  

·       Effective hand washing and suitable PPE can help reduce the spread of both viruses.

·       Flu is a much older virus, and several effective antiviral treatments and vaccines are available. There are no treatments or vaccines yet available for Covid-19. 

Sources for the article:

·       General: https://www.who.int/

·       Incubation period: https://annals.org/aim/fullarticle/2762808/incubation-period-coronavirus-disease-2019-covid-19-from-publicly-reported

·       How flu spreads: https://www.cdc.gov/flu/about/disease/spread.htm

·       Symptoms: https://www.nhs.uk/conditions/coronavirus-covid-19/symptoms-and-what-to-do/ and https://www.gosh.nhs.uk/news/coronavirus-covid-19-information-children-young-people-and-families

·       Loss of taste from the Royal College of Surgeons https://www.entuk.org/sites/default/files/files/Loss%20of%20sense%20of%20smell%20as%20marker%20of%20COVID.pdf

·       Mortality rates: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/873713/01-spi-m-o-consensus-statement-on-2019-novel-coronavirus-_covid-19_.pdf

·       Hospitalisation rates: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/873713/01-spi-m-o-consensus-statement-on-2019-novel-coronavirus-_covid-19_.pdf

·       Pre-symptomatic infection: https://www.cdc.gov/mmwr/volumes/69/wr/mm6914e1.htm#contribAff

·       Transmission and infectivity: https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-transmissibility-25-01-2020.pdf

·       Symptoms: https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-symptom-progression-11-03-2020.pdf

·       John Hopkins University Covid-19 resources: https://coronavirus.jhu.edu/map.html

·       Vaccines: https://www.sciencemag.org/news/2020/03/record-setting-speed-vaccine-makers-take-their-first-shots-new-coronavirus

·       Chats with scientists: Professor Openshaw, Professor Paul Hunter, UEA