Although Respiratory Syncytial Virus (RSV) is so common that most children have been infected with the virus by age two, most of us haven’t heard of it. So what exactly is RSV? 

RSV causes infections of the lungs and respiratory tract. In healthy adults and older children, RSV symptoms are mild and are very similar to the common cold, however, in infants, the virus can cause serious illness including bronchiolitis and pneumonia. 

In New Zealand, RSV is the most common cause of hospitalisations for lower respiratory tract infections for under two-year-olds, with influenza/flu admissions being much less frequent. Like many other respiratory illnesses, Māori and Pacific children are disproportionately affected having three-to-five times as many hospitalisations as other groups. 

Immunity to RSV develops over the first couple of years of life, however, it is never fully complete, and tends to decline again with age. This means elderly people can also be seriously affected with the virus. 

Furthermore, the RSV virus has a significant health burden worldwide, with the World Health Organisation estimating that RSV accounts for more than 60% of severe respiratory infections in children and more than 80% in infants younger than one-year-old. 

Although there are vaccines in various stages of trials, there is currently no vaccine readily available for RSV. However, the COVID-19 lockdown last year had a significant impact on the number of New Zealand children hospitalised with the RSV virus. 

A 2020 study led by Dr Adrian Trenholme and Dr Webb at Kidz First Hospital in South Auckland, demonstrated the impact of COVID-19 public health interventions on the burden of RSV in New Zealand. With the closure of New Zealand’s borders and other measures such as hygiene and mask-wearing from March 2020, the hospital saw a significant reduction in hospitalisations of infants for respiratory illness. Even after easing of the national lockdown at the end of April, the reduction continued and the usual winter peak of RSV hospitalisations and Influenza infections didn’t occur in 2020. Furthermore, data from the National Virus Surveillance in New Zealand confirms the dramatic changes in influenza and RSV infections in all age groups. 

It is evident that the New Zealand COVID-19 elimination strategy helped stop the spread of seasonal RSV and influenza virus, with similar findings having been reported in Alaska, Finland, and Australia. 

The study concluded that international border controls had the biggest impact on the absence of RSV and influenza during what would usually be the peak winter season. This included the 14-day mandatory isolation of arriving passengers, which limited seasonal viruses getting into the country. Physical distancing and hygiene measures undoubtedly contributed as well. 

However, the question remains, will we see the same outcomes this winter with New Zealand’s border controls still in place? Western Australia saw a large surge in RSV cases at the end of 2020 (see Figure 1); which was not expected, and outside the usual season. This could be due to Australia having RSV circulating all year round in some areas, with an outbreak not linked to international arrivals. However, New Zealand’s rates are very seasonal, and if RSV were to appear in our community, we now have a population group with no immunity who may be very vulnerable to it. 

Figure 1: Rates of RSV detected in Australia 2020 

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