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  • Writer's pictureEva

Coronavirus vs. swine flu

Hi I saw your Facebook post and wanted to know is this covid 19 coronavirus similar to the swine flu pandemic, what’s the difference as swine flu seems to have gone? Will coronavirus do the same?

When coronavirus, scientific name SARS-CoV-2, was declared a pandemic by the WHO on 11th March, it had been about a decade since the last pandemic was declared. That pandemic was of H1N1 virus, which causes swine flu. It was estimated that 11-21% of the global population became infected with swine flu during this pandemic in 2008. There are a few immediate differences between the swine flu and coronavirus pandemics, Firstly, although highly debated, mortality rates of swine flu seemed to be similar to that of seasonal flu; whilst COVID-19 appears to be higher. Another difference is the vulnerable groups - whilst coronavirus primarily affects older people, 80% of swine flu’s infections were in people under 65. In the summer of 2010, WHO declared the swine flu pandemic to be over, it is now one of the seasonal flues that come round every year.

How do these two pandemics differ and what happened to H1N1 in 2010?

There are many reasons as to why pandemics vary in their nature, including how early we detect the outbreak, the timing of the pandemic and how quick we are to develop vaccines and diagnostic tools. Many differences become clear when looking at how the two viruses differ biologically.

H1N1 is a type of influenza A virus. Influenza A viruses cause the seasonal flu every year and one strain of the H1N1 type resulted in the deadly 1918 flu pandemic. Other influenza viruses, including ones that cause bird flu, make up the rest of this family, called orthomyxoviridae. SARS-CoV-2 is part of a completely different family of viruses, called coronaviruses. Their name - ‘corona’ - comes from their crown of spike proteins that can be seen using an electron microscope. This family includes the viruses which cause the common cold as well as those that cause SARS (epidemic in 2003) and MERS (outbreak in 2012). SARS and MERS were much more fatal than COVID-19 with respective mortality rates of 10% and 35%, but had a much lower infection rate than SARS-CoV-2.

The H1N1 strain that caused swine flu was very similar to Spanish influenza flu and the seasonal flues we experience every winter. This meant existing antivirals worked against H1N1 and, by slightly altering existing seasonal flu vaccines, a successful swine flu vaccine was made in September 2009. The vaccine could add to the existing immunity that was being built up against the virus. Interestingly, older people were not affected by swine flu as they had already built immunity against a previous seasonal flu that was similar enough to cross-protect against this H1N1 strain! This build up of herd immunity meant that now swine flu is not a pandemic but a seasonal flu.

Coronaviruses cause common colds and were not considered a danger until the SARS outbreak in 2002. For this reason much less is known about them, even how to properly classify them or how they work. This makes it harder to fight SARS-CoV-2, particularly with no existing antivirals or vaccines to work against them. It’s unclear whether the common cold has given us any immunity against SARS-CoV-2 like seasonal flu had for swine flu. Both MERS and SARS disappeared by containment, making the virus eventually die out. It’s unclear at this point whether SARS-CoV-2 will follow a similar pattern or, due to its higher infectivity and much lower mortality, behave like swine flu and become seasonal due to herd immunity.

Although there are many factors, both within and beyond our control, that influence the nature of pandemics, the biological differences between the viruses that cause swine flu and COVID-19 are likely to play a role. The more we learn about coronaviruses the better equipped we become to defend ourselves against them. From the swine flu pandemic we can see that this knowledge is not just useful for today - but could come to our rescue if another outbreak were to occur in the future.

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