Comparing Covid: A Copy-Paste

Professor Francois Balloux is Director of the University College London Genetics Institute and a professor of Computational Systems Biology.  He’s someone else I’ve discovered recently on Twitter who is a voice of calm and common sense.  Below is a copy-paste of his latest series of 13 tweets, comparing Covid-19 to Influenza.  It supports the relevance of my question: why has the World Health Organisation’s 2019 Non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza not been the standard reference guide for best practice in responding to this pandemic?

Many discussions about #COVID19 boil down to wether the virus is ‘just like the flu’ or ‘nothing like the flu’. As such, I felt it may be useful to provide a comparison of some of the major epidemiological features of the two viruses. 1/13

To provide a meaningful comparison I will focus on pandemic flu (influenza A). The last flu pandemics happened in 1918, 1957, 1968 and 2009. The descendants of the 1918, 1968 and 2009 influenza strains are still in circulation today. 2/13

Chart Human Pandemics

Transmissibility (R0): The basic reproduction number (R0) is a measure of the growth of an epidemic in a population with no immunity. It lies around 2.0-2.5 for #COVID19, which tends to be towards the higher end of those recorded during the last four flu pandemics. 3/13

Mode of transmission: Influenza is transmitted primarily between people through respiratory droplets, and more rarely by aerosols or self-inoculation of the nasal mucosa by contaminated hands. The same looks true for #COVID19. 4/13

Infection Fatality Rate (IFR): The most recent estimates of #SARSCoV2 IFR are ~0.6%±0.3%. This in line with the 1957 influenza pandemic (~0.67%), higher than for the 1968 and 2009 pandemics, and far below the 1918 pandemic (>2.5%). 5/13

Age risk: Influenza is particularly dangerous for young children and the elderly. The 1918 pandemic was unusual with young, healthy adults also at high risk. #COVID19 is dangerous for people >60 and children are at essentially no risk, relative to other causes of death.  6/13

Influenza deaths

Asymptomatic infections: Around ~70% of infections by #SARSCoV2 are asymptomatic. Serological surveys for influenza showed that the number of asymptomatic cases was 50-75% for the flu. The two viruses are fairly similar in that regard.  7/13

Complications: Any life-threatening infection requires time to fully recover from and can lead to long-term sequelae. This is true for influenza and #COVID19, which have both been linked to a wide spectrum of long-term adverse consequences.  8/13

Vaccines: Vaccination against influenza began in the 1930s. The efficacy of flu vaccines is generally good. Though, all influenza pandemics became endemic before a significant fraction of the population could be vaccinated. #COVID19 vaccines should be easier to develop. 9/13

Drugs: There is no effective antiviral drug for either influenza or #SARSCoV2. The ‘best’ flu drug, oseltamavir (Tamiflu) reduces symptoms by a day, comparable to remdesivir for #COVID19. Administration of corticosteroids reduces mortality in severe #COVID19 infections. 10/13

Seasonality: As is typical for respiratory virus, influenza A and #COVID19 transmit best in cold and dry air. This does not preclude transmission all year long, but we can expect #COVID19 to become highly seasonal, with a yearly peak in winter and possibly one in spring.  11/13

Pandemic Waves

Summary: #SARSCoV2 behaves in most ways like a pandemic influenza strain. The only major epidemiological difference between #COVID19 and flu pandemics is the age risk distribution, with influenza being highly dangerous to young children in addition to the elderly.  12/13

Conclusion: At this stage, #COVID19 is really ‘like pandemic flu’, but not like ‘seasonal endemic flu’. Interestingly, the 1889 Russian flu pandemic might have been caused by HCoV-OC43, which is now one of the four ‘common cold’ coronaviruses in circulation. 13/13


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