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Flu and coronavirus

The COVID-19 death rate is higher in European countries with a low flu intensity since 2018, says a working paper by Chris Hope of Cambridge Judge Business School.

Photo of man with flu.

The death rate from COVID-19 (coronavirus) in Europe appears to be linked to low-intensity flu seasons in the past two years as the same people are vulnerable, says a working paper by Dr Chris Hope, Emeritus Reader in Policy Modelling at Cambridge Judge Business School.

Dr Chris Hope
Dr Chris Hope

Although the working paper is “very much a first attempt to investigate any link between the COVID-19 death rate and flu intensity,” the results do find a “significant negative correlation” between lower flu intensity and higher death rates from coronavirus – showing that more COVID-19 deaths have occurred where there have been fewer flu deaths the past two seasons.

“The paper does not seek to make judgments about whether individuals were fortunate or unfortunate with regard to flu or coronavirus, or to evaluate governments’ response to either illness,” says author Chris Hope. “It simply reports my initial statistical findings as a policy modeller regarding the apparent statistical relationship between flu-season severity and COVID-19 deaths. The correlation with flu intensity can’t explain everything, or even most of the variation in COVID-19 deaths, but it does appear to be significant, and there is a plausible causation theory. Surely that warrants further investigation.”

In the UK, for example, there are about 20,000 excess deaths from influenza in a typical year according to Public Health England, however, there were only about 1,700 excess flu deaths in 2018-2019 and there is anecdotal and statistical evidence that the 2019-2020 flu season was also very mild in the UK, the paper says.

“This implies that there were over 30,000 people alive in the UK at the start of the COVID-19 pandemic who would have been expected to die in the previous two flu seasons. These people are likely to have been predominantly elderly and in poor health,” says the working paper, entitled “COVID-19 death rate is higher in European countries with a low flu intensity since 2018”.

Flu intensity in most European countries is measured weekly during flu season by the European Influenza Surveillance Network (EISN) on an intensity between one (baseline) and five (very high); the mean value above the baseline for 32 countries measured in Europe in all 35 weeks measured over the past two flu seasons is 29.5.

Deaths from COVID-19 up to 10 June 2020 are also available for most of the same countries from the European Centre for Disease Control and Prevention (ECDC); the mean value for the 32 European countries is 20.3 deaths per 100,000 population from COVID-19.

The working paper then compares flu intensity and COVID-19 deaths for the 32 countries to establish a “trend line” showing the best estimate of the relationship between them.

Belgium, which has the highest death rate of the 32 countries from COVID-19 and also lies 36 per 100,000 above the trend line, “had the lowest flu intensity apart from Scotland,” says the working paper. Other countries with COVID-19 death rates well above the trend line include England (33 per 100,000 above the trend line), Italy (35 above), France (30 above) and Ireland (25 above). Sweden, which chose not to have a stringent coronavirus lockdown, had a COVID-19 death rate of 16 deaths per 100,000 above the trend line.

There is also a set of countries with a death rate well below the trend line, including Norway at 34 deaths per 100,000 below the trend line and Germany at 13 deaths per 100,000 below the trend line.

The working paper acknowledges that the comparison between flu and COVID-19 has some shortcomings, including that some weeks are not covered by the ECDC in measuring flu intensity and that not all countries have adopted the same procedures in measuring COVID-19 deaths.

“Despite these shortcomings, the results do suggest that the relationship between COVID-19 deaths rates and previous flu intensity would be worth further and fuller investigation,” says the working paper. “Further investigation should be able to determine whether the relationship is as significant as this first analysis suggests.”

The paper also suggests more research to look in-depth at what the five countries well above the trend line have in common, including whether they have been more thorough in reporting coronavirus deaths or showed a possible lack of attention to care homes early in the pandemic.

Chris Hope’s widely cited models on climate change have been used by the UK’s Stern Review, the US Environmental Protection Agency and other public bodies to estimate the social cost of carbon dioxide. He recently wrote a working paper on voluntary infection as a way to exit COVID-19 lockdown.