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Commentary: COVID-19 has created an ‘immunity debt’ towards common infections in our children

As countries remove COVID-19 measures that curb the spread of the coronavirus and other viruses, it’s not surprising that Singapore is seeing more respiratory illnesses in our children, say KK Women’s and Children’s Hospital doctors Matthias Maiwald and Thoon Koh Cheng.

SINGAPORE: COVID-19 has been a big disruption to the world. Pandemic response measures not only helped keep the coronavirus at bay, but also had the effect of curbing the spread of other respiratory illnesses like the common cold and influenza.

But as restrictions are relaxed or lifted with the widespread use of vaccines and antivirals, several viruses and bacteria are now making a comeback.

It makes sense that measures targeted at preventing COVID-19 reduced the spread of infections transmitted via respiratory droplets. People stopped travelling, worked from home, wore masks and stayed in when unwell.

Combined data from KK Women’s and Children’s Hospital (KKH), Singapore General Hospital and National University Hospital showed that most non-COVID-19 respiratory viruses nearly disappeared by April and May 2020, when Singapore went into a "circuit breaker" period.

People wearing masks cross the road at South Bridge Road in Singapore on Feb 22, 2022. (Photo: CNA/Gaya Chandramohan)

With the reopening in phases in late 2020, some respiratory viruses gradually returned, though not at pre-pandemic levels, since mask-wearing in public continued.

Amid concerns about the Delta and Omicron variant waves in the second half of 2021 and early months of 2022, healthcare professionals saw non-COVID respiratory illness levels drop again after response measures were tightened and subsequently come up when eased. Similar effects were seen overseas. Also, the usual flu seasons were absent.


The return of respiratory viruses is not surprising to healthcare experts.

The first ones to return, in late 2020, were the rhinoviruses and enteroviruses which usually cause mild common colds. Then, early 2021 saw a reappearance of the respiratory syncytial virus (RSV) and some parainfluenza viruses, both of which may cause more serious illness in young children, such as bronchiolitis or croup, which has a distinctive barking cough.

What is surprising is the unusual pattern of activity of viruses that usually have a predictable seasonality.

In Australia, the United States and Europe, waves of RSV infections were recorded outside the traditional winter months. Several countries, at some point, reported that RSV waves were stretching the capacity of children’s hospitals that were already under pressure from COVID-19.

Another observation was that RSV infections occurred in older children, whereas before the pandemic, children less than one-year-old were mostly affected. In some locations, the numbers of RSV infections even surpassed those of COVID-19 paediatric infections at times.

What might explain these changes? Due to all the pandemic response measures, young children, including those born during the pandemic, have had much less exposure to common respiratory viruses than same-age children in pre-pandemic years.

This created an “immunity debt” towards previously common infections, meaning that the lack of exposure to viruses and bacteria during the pandemic left children more susceptible to various infections.


Can we expect to see other respiratory illnesses make a comeback? Probably.

Influenza viruses (there are A and B strains) nearly disappeared during the pandemic, and only a small number of influenza infections were observed again in the first half of 2022, according to data from KKH. These numbers are expected to rise in the second half of 2022; Australia is currently experiencing a substantial rise in influenza infections, and international travel is likely to bring this to Singapore soon.

Before the pandemic, KKH regularly diagnosed bacterial respiratory infections, such as Mycoplasma pneumoniae (which causes pneumonia predominantly in children) and Bordetella pertussis (the agent of classical whooping cough). These infections also disappeared during the 2020 circuit breaker and have not reappeared up until mid-2022.

Parents may also be concerned about children getting multiple infections. In June, Singapore recorded the first paediatric COVID-19 death in a one-and-a-half-year-old boy who had COVID-19, RSV and enterovirus infections.

With Singapore recording a seven-day moving average of 3,750 COVID-19 cases (as of Aug 18) and yet another Omicron subvariant, various respiratory viruses are also returning with relaxation of some of the earlier pandemic measures.


What does this all mean for us in Singapore? Respiratory viruses have been with us for a very long time and are part of what helps train our immune systems and those of our children.

It is their absence, rather than presence, that is an unusual state. Their return after the initial phases of the COVID-19 pandemic should be seen as part of the return to normality.

But we should still take precautionary measures and stay vigilant, due to the possibility of severe illnesses in some children and vulnerable adults.

This means we should take good care of ourselves and our children and seek medical care if infections look to become more serious. Signs to look out for in children are worsening or persistent fever, lethargy or drowsiness, persistent cough, breathlessness, chest pain, poor oral intake, poor urine output, or seizures.

It is also recommended that we keep our influenza vaccinations up to date. Anyone above six months of age can obtain their influenza vaccination at their local general practitioner (GP) clinic or polyclinic.

COVID-19 may have changed the way we think of and live with viruses, and we should keep up some of the habits we have picked up along the way.

Associate Professor Matthias Maiwald is the head and senior consultant in the Microbiology Service, Department of Pathology and Laboratory Medicine. Associate Professor Thoon Koh Cheng is a senior consultant in the Infectious Disease Service, Department of Paediatrics. Both are at the KK Women’s and Children’s Hospital.

Source: CNA/ch


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