The 2020/2021 influenza season was remarkable — for its low number of infections. This is hardly surprising, given that the flu virus spreads via droplets, just like SARS-CoV-2, which we all know simply as "coronavirus" and which causes COVID-19.

And we've all learned to reduce that risk over the past year-and-a-half: We've been wearing face masks, keeping distance from people in public, washing our hands often, and sanitizing stuff. (Well, many people have, in any case.) That has helped slow the spread of COVID-19 — as well as that of the common cold.

This was all confirmed in a recent edition of the monthly influenza report by Germany's Robert Koch Institute, the country's center for disease control and prevention.

It said there had been no "measurable" wave of flu infections in Germany or in other European countries during the 2020/2021 flu season. 

The World Health Organization reported a similar trend in its recent influenza update.

With regard to its global figures, the WHO says that "despite continued or even increased testing for influenza in some countries, influenza activity remained at lower levels than expected for this time of the year."

Fewer infections reported

The same is true of other infections. The RKI reports a drop of 35% in general infectious disease cases between March and August 2020. 

The biggest reduction was among respiratory infections — that is, those that spread through the air. Measles infections, for instance, were down by 86%. Whooping cough was down by 64%.

Even gastrointestinal infections decreased: Rotavirus infections dropped by 83%, and norovirus infections by 79%.

But the reasons for the drop in infections varies from virus to virus, say the experts.

Restrictions on in-person contact and other hygiene regulations have played a part, especially for gastrointestinal infections.

There was also a drop in the number of sexually transmitted infections and those transmitted via the blood.

And HIV infections dropped by 22%, which the RKI thinks may have to do with restrictions clinics and counseling centers have faced during the pandemic.

However, it is just as conceivable to think that a large number of any type of infection has gone undetected, with people avoiding unnecessary trips to the doctor or the hospital during lockdown. 

As a result, it's possible that there is a very high number of unknown or unreported cases of illness.

RSV cases rise in children

In some parts of the world, the number of cases of respiratory syncytial virus (RSV) has increased among children.

The US Centers for Disease Control and Prevention describes RSV as a common respiratory virus that "usually causes mild, cold-like symptoms. Most people recover in a week or two; but RSV can be serious, especially for infants and older adults."

The RKI's assessment is similar. It says RSV can affect people of all ages, but that it most often impacts infants.

RSV is highly infectious. It is transmitted when an infected person sneezes or coughs — the same route SARS-CoV-2 uses.

In March, there were a number of RSV cases in Australia. In New Zealand, the number of cases has risen consistently since the end of May.

Meanwhile in Central Europe, where RSV cases tend to rise between November and April, that traditional "RSV season" was relatively quiet.

But cases are starting to present themselves now. France, Switzerland and the United Kingdom are reporting ever more RSV cases.

The Royal College of Emergency Medicine wrote in June that emergency centers in the UK were seeing a "dramatic rise in the number of young children — but it's not COVID."

RSV symptoms include runny nose, coughing, reduced appetite and fever. It can also develop into acute bronchitis or pneumonia. An RSV infection is one of the most common reasons for hospital admissions among infants and young children.

Germany's RKI estimates a worldwide RSV incidence rate of 48.5 cases per 1,000 children in the first half of 2021; 5.6 cases per 1,000 kids is considered to be severe.

From 50% to 70% of kids get at least one RSV infection in their first year after birth. By the time kids turn two, almost all of them have had a RSV infection.

'Winter in June'

Emergency admissions at UK hospitals are on the rise at the moment, with cases of RSV — which usually happen in the winter — happening now in the summer (in the northern hemisphere).

This is putting accident and emergency centers in the UK under a lot of extra pressure, reports the Royal College of Paediatrics and Child Health. It says worried parents have been bringing their kids in with just the slightest fever. One emergency doctor described the situation as "winter in June." 

Small wonder. A lot of parents may have forgotten what to do when their kids get a fever, or they may have never experienced it at all yet — especially if their babies were born during lockdown.

The Royal College of Emergency Medicine has even published guidance to help parents with small children; because in many cases, there's no need to take your kids to the emergency room.

"In most cases of mild fever, runny nose or cough, simple self-care measures such as taking paracetamol or ibuprofen can help," writes the Royal College. It adds that in cases where parents are concerned, seeking medical assistance from a pharmacist, family doctor or a medical hotline are all appropriate moves.

Disrupted balance

German virologist Sandra Ciesek had described in March how we usually live in natural "balance" with viruses — but how that had been disrupted by the pandemic. Ciesek heads the Institute of Medical Virology at Frankfurt's University Clinic.

Speaking in a podcast, Ciesek explained how kids had been cut off or sealed away from viruses and other illnesses. 

That happened when schools shut and face coverings became obligatory in public, and people limited their social contacts — they were cut off from the viruses that would normally confront them regularly. 

"It just shows how we usually coexist with viruses. And it shows how artificial conditions, like limiting personal contacts, can influence [the spread of] viruses, and that rates of infection can get artificially moved from [one season to another]," said Ciesek in March.

Immune systems catching up

Out of balance does not, however, mean out of practice. Pediatricians in Germany are reporting "a slight increase" in RSV infections, Jakob Maske, a spokesperson for the Professional Association of Pediatricians, said to the dpa news agency. "But we're relatively relaxed about it."

Maske suggests children are merely catching up with the infections that they would have had earlier had it not been for the coronavirus pandemic and the lockdowns.

"RSV causes a common cold, you wouldn't normally look for it as such. The risks are less than those associated with COVID-19 or flu," he said. 

In fact, said the pediatrician, "it's normal to see kids getting these infections. Sure, we'll see slight increases over the coming months. The main difficulty with a runny nose is telling the difference between COVID and a common cold." 

The immune system is 'not a muscle'

All this begs the question: Will kids have more severe infections after the COVID-19 pandemic if their immune systems missed out "training" during winter lockdowns?

Carsten Watzl, the secretary general of the German Society for Immunology, says we may see more infections, but not necessarily more severe ones.

Watzl says the immune system is not like a muscle that's become weak during the pandemic.

He says our immune systems have had enough to do, even during lockdown, because germs also enter our bodies other ways, such as through food.

"The rhinovirus [another common cold virus], for instance, keeps changing and always appears to the immune system as new," he says. 

Strategy versus nature

After a while, it's just your turn again. You're going to get sick.

And because of the various lockdowns, says Watzl, more people will get sick when lockdown has been lifted. We will, he says, probably see more common colds and RSV infections. But he doubts we will see more rhinovirus infections.

In a strategy paper for autumn, the RKI warned that hospitals and emergency centers should prepare early for higher numbers of general infections. It cites respiratory viruses that did not circulate as much during the 2020/2021 season. Infections will include flu and — it goes without saying — SARS-CoV-2. 

This article was translated from German.