Explainer: Are children in Singapore facing a 'tripledemic' threat of influenza, Covid-19 and RSV?

SINGAPORE — Health experts have warned of a possible “tripledemic” where three major respiratory viruses could collide and sicken children at the same time, namely the respiratory syncytial virus (RSV) and the ones causing influenza and Covid-19.

And with increasing travel and the relaxation of safety and hygiene measures in the community, these three highly infectious viruses are taking a toll here, even though infection numbers seem to be trending down since last month, they added.

The Ministry of Health’s weekly bulletin showed that the incidence of acute respiratory infections among people across all ages at polyclinics was high in September and October, with the highest number of infections standing at 3,514 in the second week of October.

This was triple the number of acute respiratory infections recorded in the same week last year, which was 1,168.

Dr Jyoti Somani, a senior consultant at the infectious diseases division of the National University Hospital (NUH), said that influenza is known to cause severe disease, especially in older people, but so far this year, there have been no “very severe” cases among seniors at the hospital.

However, at the other end of the age spectrum, it is a different story. There are significantly more cases of RSV, influenza, and rhinovirus or enterovirus — about 80 to 90 per cent — in children aged under 18 than in adults within NUH now.  Rhinovirus and enterovirus are viruses behind the common cold.

This high proportion of younger patients includes some with co-infections of other viruses such as metapneumovirus, another common virus that causes an upper respiratory infection.

Experts said that this could potentially be due to the “immunity debt” children have as a result of Covid-19 restrictions, making them more susceptible to previously common infections now.

TODAY looks at how this tripledemic is infecting the young ones and whether immunity debt may be a big contributor. 

HOW IS THE TRIPLEDEMIC INFECTING CHILDREN?

Experts said that the three highly contagious respiratory viruses cause similar symptoms such as fever, cough, runny nose and sore throat, and it is possible for a person to be infected with multiple viruses at the same time.

Dr Rie Aoyama, a paediatric infectious diseases associate consultant at NUH’s Khoo Teck Puat – National University Children's Medical Institute, said that RSV can also cause severe or life-threatening infection in infants under the age of one and those born prematurely, those with underlying heart or lung conditions, or those with weakened immune systems.

“These children are more likely to be hospitalised and require oxygen and mechanical support to help them breathe,” she added.

In Singapore, RSV occurs regularly throughout the year with the main peak in June or July coinciding with the southern hemisphere winter season, and a smaller peak at the end of the year coinciding with the northern hemisphere winter season, Dr Aoyama said. 

The peak activity of RSV and influenza can occur together, putting children at risk of being infected with both viruses.

"We are currently entering the northern hemisphere winter season, and with increasing travel, the increase of all three viruses is seen in many countries throughout the world,”  Dr Aoyama added, referring to Covid-19 as the third of the three.

Dr Somani noted that some paediatric patients in NUH are admitted for infections of multiple respiratory viruses, such as Covid-19 and influenza, or co-infections with other viruses such as the rhinovirus.

And this may be a concern to many parents. In June, Singapore recorded the first paediatric Covid-19 death in an 18-month-old boy who had Covid-19, RSV and enterovirus infections.

WHAT IS IMMUNITY DEBT?

Though it is a matter of concern, the return of respiratory viruses is not surprising to healthcare experts, mostly due to the “immunity debt” children have.

Many experts have hypothesised about the impact on infection rates after the Covid-19 pandemic when people wore masks and engaged in social distancing.

The theory goes that Covid-19 measures also protected people from being infected by a range of viruses. A lack of regular exposure to these other viruses have led to people's immune systems becoming less effective at fighting them.

That is why more people than usual would be catching certain diseases for the first time now since restrictions have been largely lifted. This theory, though, is still being debated.

Dr Paul Tambyah, president of the Asia Pacific Society of Clinical Microbiology and Infection, said: “The concept of ‘immunity debt’ is right now just a hypothesis.

"As we and others have shown, in Singapore, apart from the ‘circuit breaker’ (partial lockdown) period of April to May 2020, respiratory viruses never actually disappeared, with the notable exception of influenza.”

Dr Somani said that influenza was almost absent from May 2020 to December 2021, and Singapore started to see flu cases again only in February this year. Experts have linked this absence to the broken chain of transmission caused by the near-complete shutdown of global travel.

They also said that the absence of such viruses has caused young children born during the pandemic to have much less exposure to common respiratory viruses than children of the same age in previous years.

Dr Aoyama said: “Having one viral infection may lower the child’s immunity such that they are more vulnerable to another co-existing or subsequent viral infection, or occasionally, bacterial pneumonia.”

Similarly, Dr Matthias Maiwald, head consultant of microbiology service at KK Women's and Children's Hospital (KKH), said that because children had not been much exposed to RSV since 2020, this virus may now infect slightly older children than was the case before the pandemic.

“The lack of exposure to viruses and bacteria during the pandemic has left people, in particular young children, more susceptible.

“With the easing of safe management measures and resumption of travel, the return of respiratory viruses is expected — meaning that many of us will again have flu-like illnesses off and on. This is also reflected among the patients that our hospital is seeing, although it is difficult to put a percentage figure on this,” he said. 

HOW CAN WE PROTECT THE YOUNG ONES?

Experts said that it is too early to tell if Singapore has crossed the peak of this tripledemic because a lot will depend on the activity in temperate countries and the people returning to Singapore from holidays there.

Dr Tambyah said: “Those peaks can be any time from November to February, so we may have another peak in January or February, perhaps with the Chinese New Year (festivities).

"For Sars-CoV-2, we have passed the current peak and I think it will be some time before the next one, so I do not think that we will have another coincidence of peaks for the three viruses this season."

This refers to the virus behind Covid-19.

In the meantime, adults around young children should practise good hand hygiene and respiratory etiquette, the experts advised.

Dr Aoyama said that anyone who is unwell and showing symptoms should stay at home as much as possible, wear a mask and avoid social gatherings.

“With increasing travel and the removal of restrictions for large crowds and gatherings, being socially responsible is really important to protect those around us from being unwell with these common viral infections.”

She added that the flu jab is strongly recommended for children above the age of six months and is included in the national childhood immunisation schedule.

Dr Li Jiahui, head of the infectious disease service at KKH, said that parents are advised to take their child to a general practitioner, paediatrician or to a hospital emergency department if infections look to become more serious.

Signs to look out for in children are:

• Poor feeding
• Worsening or persistent fever
• Lethargy or drowsiness
• Persistent cough
• Breathlessness
• Chest pain
• Poor oral intake
• Poor urine output
• Seizures