Winter typically brings a surge in respiratory viral infections, when we see many children running around with runny noses and phlegmy coughs.

But the 2020 Australian winter was very different. Public health measures in place to control the spread of COVID-19 saw a major shift in the typical seasonal pattern of other respiratory viruses.

This has perhaps been most notable with respiratory syncytial virus (RSV), a very common cause of hospitalisation in young children over winter months in many parts of the world, including Australia.

But following an abnormal winter that saw a significant drop in rates of RSV — we found there were 98% fewer winter cases in Western Australian children — paediatric hospitals around Australia have seen unexpectedly large numbers of children presenting with RSV over summer.

So, what is RSV, and why are these changing trends important?

A winter lurgy

RSV typically circulates during winter in temperate climates, much like influenza.

It’s the major cause of lung infections in children, commonly causing bronchiolitis. Symptoms of RSV include a runny nose, cough, reduced feeding and fever. Complications include wheezing and difficulty breathing, which can develop into pneumonia.

Severe cases occasionally lead to death, predominantly in very young infants.

Almost all children have had an RSV infection by age two, but infants in their first year of life are more likely to experience severe infections requiring hospitalisation, because their airways are smaller. Babies have also not built up immunity to RSV from previous years (we call this being RSV-naïve).

RSV is spread through respiratory secretions, when an infected person sneezes or coughs. In this way it’s similar to COVID-19. But in contrast to the coronavirus, children are more vulnerable to RSV infection than adults. As a result, RSV is readily spread among children, especially at daycare, kindergarten and school.

Who’s most at risk?

Both young and old people are most at risk of severe disease.

For children, those most at risk of severe disease include babies under two months old, premature infants, those with other medical conditions, or ones infected with another virus at the same time. First Nations children are three to six times more likely to be hospitalised with bronchiolitis caused by RSV than non-First Nations children.

Otherwise healthy children under 12 months old (usually under six months old) are the ones most often admitted to hospital. Of children admitted to hospital, about a quarter (26%) will be admitted to intensive care.

How is RSV treated?

Most children will recover without needing specialist care in hospital, and children with mild infection can be treated with rest at home.

However, many children, particularly young infants, those born prematurely, and children with underlying health issues, are admitted to paediatric wards with severe RSV every year.

Treatment for RSV is focused on helping children with their breathing (for example, giving them oxygen) and feeding (for example, administering fluids through a drip).

There’s no licensed vaccine for RSV, but the World Health Organization considers this a priority, and a number of vaccines are currently in development.

A doctor holds a stethoscope to a baby's chest.
Infants under one are more vulnerable to a serious case of RSV. Shutterstock

What happened to RSV in 2020?

The stay-at-home orders across Australia from late March 2020, and the implementation of quarantine for international arrivals, coincided with the start of the usual RSV and influenza season in Australia.

With these measures in place, RSV and influenza cases dropped dramatically and remained very low throughout winter.

In Western Australia, despite a relaxation of COVID-related restrictions, including schools reopening from May 2020, there was still a dramatic reduction in RSV cases through winter. This suggests border closures were important in reducing transmission from arriving overseas travellers.

RSV cases remained low until late spring, when a large surge was observed in New South Wales and WA.

The speed and magnitude of this increase was greater than the usual winter peak of RSV.

More recently, other states including Victoria and Queensland have seen a similar unseasonal rise in RSV cases.

It’s likely reductions in COVID-19 restrictions have opened the door for increased RSV spread. Reduced immunity to RSV may also have contributed through both an increase in number of RSV-naïve children and possibly waning RSV immunity in older children related to the delayed season.

Studies seeking to understand exactly why we’ve seen a rise in RSV cases are ongoing.

Why might the Australian surge be important elsewhere?

Australia’s experience may carry important lessons for Northern Hemisphere countries, including the United States and the United Kingdom, which saw similar reductions in RSV cases during their winter.

Relaxing of COVID restrictions, which is beginning in many Northern Hemisphere countries now, may provide an opportunity for rapid spread of RSV. Our experience should serve as a warning for paediatric hospitals in the Northern Hemisphere to ensure adequate staffing and available resources to meet the possible increased need.

Three young children playing with various toys.
Children mixing less as a result of COVID-19 restrictions likely contributed to the drop in RSV cases during winter. Shutterstock

Our RSV experience may also be applicable to influenza, which still remains at very low levels globally. Reduced immunity to influenza due to the skipped 2020 season may result in a very severe season when influenza returns. Seasonal influenza vaccines could be particularly important in 2021 to protect against a possible large resurgence.

Let’s hold on to our good COVID habits

The COVID-19 pandemic has shown us the spread of respiratory viruses can be reduced by physical distancing and increased hygiene measures.

While we are (hopefully) unlikely to see prolonged stay-at-home orders again in Australia, ongoing basic measures including hand washing, cough etiquette and keeping snotty children at home can all help reduce the spread of RSV and influenza moving forward.

As we approach the 2021 Australian winter, by doing these simple things, as well as getting our flu vaccines, we can all help protect children, including those most vulnerable, from these important respiratory viruses.

Is there a vaccine?

There are no vaccines to protect against RSV in Australia.

Australia’s only currently available preventative medicine is palivizumab, which is a long-acting monoclonal antibody given monthly during the RSV season. Due to its cost, it is reserved for infants at highest risk for severe RSV infection and is usually given in hospital.

However, several new preventative agents are in the pipeline.

In May this year, the US Food and Drug Administration approved the RSV vaccine Arexvy for people aged 60 and over. It is being considered for use in Australia.

Results from clinical trials for RSV vaccines given to pregnant women to protect their baby for the first six months are promising. The maternal Pfizer vaccine has demonstrated greater than 80% effectiveness against severe lower respiratory tract illness in their infants for the 90 days after birth.

However, safety data is being closely examined, including a potential risk of premature birth.

How can I protect my children in the meantime?

Parents can minimise the risk of RSV by using many of the measures we’ve been using during the COVID pandemic. Encourage children to cover their mouths and noses when coughing or sneezing, and regularly wash their hands.

Ensuring kids stay away from school, childcare or other children when sick helps prevent the spread of many viruses, including RSV.

Viral symptoms to watch out for include difficulty feeding, cough, irritability and/or rapid breathing. If parents notice these signs or are worried about their child they should seek urgent medical assessment and not delay.

This article is republished from The Conversation under a Creative Commons license. Read the original article.