As flu returns and Covid-19 cases rise, Europe faces the possibility of a long-term 'twindemic'

After nearly disappearing last winter, influenza has returned to Europe at a faster-than-expected rate this winter, generating fears of a lengthy "twindemic" with COVID-19, as well as some reservations about the efficacy of flu vaccines.

During the COVID-19 pandemic, lockdowns, mask-wearing, and social distancing were the norm in Europe, knocking out flu last winter, temporarily eradicating a virus that kills over 650,000 people worldwide each year, according to EU estimates. However, as a result of widespread immunisation, countries are adopting less stringent methods to combat COVID-19.

The term "twindemic" refers to the likelihood of a severe flu season occurring concurrently with an increase in COVID-19 cases, with the result being a combination of two diseases in the same person at the same time.

The European Centre for Disease Prevention and Control (ECDC) stated this month that flu viruses have been circulating throughout Europe at a higher-than-expected rate since mid-December.

According to ECDC and WHO data, the number of flu cases in European intensive care units (ICU) progressively increased in December, peaking at 43 in the final week of the year.

That's a far cry from pre-pandemic levels, with weekly flu cases in ICUs reaching over 400 at the same point in 2018. However, data reveal that this is a significant rise over last year, when there was only one flu incidence in an ICU for the entire month of December.

According to the ECDC's leading influenza scientist, Pasi Penttinen, the virus's reappearance could signal the start of an abnormally extended flu season that could go well into the summer.

"The great concern I have for influenza if we start to lift these restrictions is that, since we've had such a long period of essentially no circulation in the European population, we might shift away from normal seasonal patterns," he said.

Dismantling restrictive measures in the spring, he added, might extend the flu season much beyond the customary end of the European season in May.

According to the ECDC, a "twindemic" might impose undue strain on already overburdened health systems.

According to data released by the French health ministry last week, three regions in France, including the Paris region, are experiencing a flu epidemic. Others are in the early stages of an epidemic.

France has had 72 significant instances of flu so far this season, with six deaths.

Strain that is dominant:

To make matters worse, the predominant flu strain circulating this year appears to be the H3 type of the A virus, which is known to produce the most severe cases among the elderly.

Penttinen said it was too early to make a final judgement on flu vaccines because real-world assessments need a bigger number of sick individuals. However, lab studies reveal that the H3 vaccines available this year "are not going to be optimal."

This is largely due to the fact that there was little or no virus circulating when the vaccines' composition was decided last year, making it difficult for vaccine producers to forecast which strain will dominate throughout the upcoming flu season.

Vaccines Europe, which represents the region's top vaccine makers, recognised that last year's low flu circulation made strain selection more challenging, but stressed that there was insufficient data to assess the efficiency of this season's injections.

Every year, flu vaccines are improved to ensure that they are as effective as possible against ever-changing flu viruses. Their make-up is determined six months before flu season begins, based on virus circulation in the opposite hemisphere. This allows drugmakers enough time to develop and manufacture the injections.

There is currently no data on flu vaccination uptake across Europe. However, national statistics for France suggest that coverage is not as extensive as officials had intended.

To encourage vaccinations, the authorities in that country extended the vaccine schedule by one month, to the end of February. According to numbers revealed last week, 12 million people, or around 45 percent of the target population, had been vaccinated.

"There is still a large room for improvement to limit the impact of the flu epidemic," the health ministry stated in a statement on Jan. 11. The goal for this year is to vaccinate 75% of those who are at risk.

Vaccines Europe stated the sector had supplied a considerable number of flu vaccines despite the pandemic's impact on production infrastructure.