Influenza has returned to Europe at a faster-than-expected rate this winter after almost disappearing last year, raising concerns about a prolonged “twindemi” with COVID-19 amid doubts about the effectiveness of flu vaccines.
Lockdowns, mask-wearing and social distancing, which have become the norm in Europe during the COVID-19 pandemic, knocked out the flu last winter, temporarily eradicating a virus that kills around 650,000 a year globally, according to EU figures.
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But that has now changed as countries adopt less stringent measures to combat COVID-19 due to widespread vaccination.
Since mid-December, the flu virus has been circulating in Europe at a higher rate than expected, the European Center for Disease Prevention and Control (ECDC) reported this month.
In December, the number of cases of influenza in European intensive care units (ICU) steadily rose to peak at 43 in the last week of the year, according to data from the ECDC and the World Health Organization.
It is well below pre-pandemic levels – with weekly flu cases in intensive care units, e.g. topped with over 400 at the same stage in 2018.
But that is a big increase over last year, when there was only one case of flu in an intensive care unit throughout December, data show.
The return of the virus could be the start of an unusually long flu season that could last well into the summer, ECDC’s top flu expert Pasi Penttinen told Reuters.
“If we start abolishing all measures, the big concern I have for the flu is that because we have had such a long time with almost no circulation in the European population, we might want to shift away from normal seasonal patterns,” he said.
He said the abolition of restrictive measures in the spring could prolong the circulation of influenza far beyond the normal end of the European season in May.
A “twindemi” could put too much pressure on already congested healthcare systems, the ECDC said in its report.
In France, three regions – including the Paris region – are facing a flu epidemic, according to data released by the French Ministry of Health last week. Others are in a pre-epidemic phase.
This season, France has so far registered 72 serious cases of influenza with six deaths.
Further complicating matters, the dominant influenza strain circulating this year so far appears to be H3 from the A virus, which usually causes the most severe cases among the elderly.
Penttinen said it was too early to make a final assessment of flu vaccines because a larger number of sick patients were needed for real-world analyzes. But laboratory tests show that the available vaccines this year “will not be optimal” against H3.
This is largely due to the fact that there was very little or no virus in circulation when the composition of the vaccines was decided last year, making it more difficult for vaccine manufacturers to predict which strain would be dominant in the coming flu season.
Influenza vaccines are adapted every year to make them as effective as possible against ever-changing influenza viruses.
Their composition is determined six months before the start of the flu season, based on the circulation of viruses in the opposite hemisphere. It gives drug manufacturers time to develop and make shots.
Vaccines Europe said the industry had delivered a large number of flu vaccinations despite the strain on production facilities caused by the pandemic.