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Could it be that flu infection dampens a covid infection wave. Like last year it seems when Flu peaks greater than covid infection the Covid wave increase is terminated at the decline commences. Could it be that flu takes out of the population people (whose behaviour makes then susceptible to respiratory infection ) who would have gone onto contracting covid and infecting others; from their flu sick bed they can't catch covid and infect others. Maybe its the difference in the infection to symptom timespan between flu and covid that is the factor, and why covid waves in winter/flu season are dampened more than the covid waves in summer when flu is not so prevalent. Also flu symptoms make take potential asymptomatic covid infectors out of the population which would not happen in a covid wave outside of the flu season?

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Interesting thought and I'm sure that there's very likely to be an interaction between Flu and Covid waves in the way you outline. Although proving the causal link from the available data would be difficult.

I did a quick search and found a UK report looking at 'Viral Evolution Scenarios' for Covid comment on the interaction with other viruses. The report comments that:

'Higher rates of infection from one virus could supress those from another leading to

sequential infection patterns. Suppression of a virus in one year could then lead to loss of

immunity in the population, increasing the risk of a severe wave the following year.'

The report can be found at the following link:

https://assets.publishing.service.gov.uk/media/620654b38fa8f5109bfe11a5/S1513_Viral_Evolution_Scenarios.pdf

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So - the only way to keep up immunity in the absence of widespread vaccination, is to get repeated infections?

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Great summary as usual!

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Very helpful & really easy to understand for us mathematically challenged readers - thanks.

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