Flu wave: the peak has not yet been reached, experts fear. A care infarction is imminent

The flu epidemic that has been ravaging the Netherlands for two weeks has not yet passed its peak. The number of people who report to their GP with flu-like symptoms has increased sharply since December 21, the day the RIVM announced the epidemic. Almost half of the people who report acute respiratory complaints have a flu infection, according to the weekly survey among GPs.

The flu wave puts a lot of pressure on healthcare. “It is super busy in the hospitals,” says internist-infectiologist Joost Wiersinga, head of the infectious diseases department at Amsterdam UMC. “Many people come to the emergency room with respiratory complaints, and the shortage of nurses makes it difficult to find a bed for everyone.” On top of that, healthcare staff themselves also fall out due to illness.

The rapid increase gives the impression that we are dealing with an exceptionally early and high flu peak. But that is not the case, according to Ron Fouchier, virologist at Erasmus MC in Rotterdam and affiliated with the National Influenza Center. “The epidemic is no earlier than other pre-pandemic years and the numbers are not yet unusually high. But what we will see this year is still difficult to predict.”

Teeth

This is because, on the one hand, since the pandemic, people may be less inclined to go to the doctor with respiratory complaints, because during the pandemic the advice was to stay at home, and that the survey may therefore reflect too low a number of patients. And on the other hand, hospitals have been testing much more for flu and other respiratory viruses since corona than before the pandemic, so that the number of patients may seem higher than other years, but may not be.

“I think we are not yet at the peak, and that the hospitals will have to step up a gear in the coming weeks. This is not even half of the numbers in the flu waves that we sometimes saw before the pandemic,” says Fouchier.

In addition to the flu virus (influenza), other respiratory viruses are now circulating widely, such as the respiratory syncytial virus (RS virus), the human metapneumovirus, the coronavirus SARS-CoV-2 and the rhinovirus.

The fact that all those respiratory viruses are now circulating so strongly is a result of the virus-limiting measures in the pandemic years 2020 and 2021. In the winter of ’20-’21 there was historically little flu, in that of ’21-’22 the peak came much later and remained lower than usual. As a result, far fewer people have had the flu or other respiratory viruses, and their immunity to them has decreased. Very young children have never ‘seen’ all those respiratory viruses. Fouchier: “Those viruses can now circulate in a group of immune-naive children that is three times as large. So there are many more viruses going around, and they can therefore infect adults more easily. All those viruses are now catching up.”

Bacterial pneumonia

It is precisely all those respiratory viruses at the same time that worry Wiersinga. “We already had the high pressure on healthcare every winter before corona,” he says. “But now a triple epidemic can arise: influenza, Covid-19, and the RS virus. The elderly and vulnerable can become very ill from all three. That can lead to such high numbers of admissions that we can no longer handle it.”

Read also: Covid-19 with flu turns out more serious

Wiersinga does not see any higher numbers of patients in his hospital who develop bacterial pneumonia after flu or another respiratory infection. “You see that complication in roughly 5 percent of patients, that is also the case now.”

The current flu wave is not caused by a more virulent flu virus strain. “There are no indications for that,” says Fouchier.

“The only real surprise is that one of the two B viruses that has been circulating for years (the Yamagata line) seems to have completely disappeared. It has not been reported anywhere since 2019 – it was already disappearing and the pandemic seems to have killed it. The other B virus, Victoria, will fill that gap this winter.”

Read also: Lockdowns are also smothering flu strains

reassurance

Influenza viruses are classified into type A and type B, and with a designation of the proteins on their outside H and N (hemagglutinin and neuraminidase). Variations of two A and two B strains have been circulating worldwide for decades – of the A type these are H1N1 and H3N2, of the B type the strains Victoria and Yamagata.

A reassurance: the composition of the flu jab has seldom matched the circulating flu variants as well as this season. Fouchier: “There is an almost perfect match.” The vaccine does not protect against infection, but it does protect against hospitalization and death.

In the Netherlands, people over sixty, healthcare workers and people with certain conditions are offered the flu jab every year. In 2021, 58 percent of this group got the flu shot, the figures for this winter are not yet known.

A version of this article also appeared in the January 7, 2023 newspaper