RSV outbreak spike in cases dwarfs past six years
In the past five weeks, the number of reported RSV cases has spiked, dwarfing records from the past six years.
The outbreak had so far grown to 2543 cases nationwide – 735 of these were reported in the last week. To put this into perspective, the annual average during winter pre-Covid-19 was just 1743.
When compared to historical reports, this year’s outbreak was unprecedented. Data from the past week put the respiratory syncytial virus (RSV) infection rate at 143 per 1 million people, and the peak may still be yet to come.
By collating data from Institute of Environmental Science and Research (ESR) weekly reports, Stuff was able to paint a stark picture of this outbreak.
ESR virologist Dr Sue Huang described this exponential increase as ‘‘very sharp’’.
Prior to this outbreak, the 29th week of 2015 held the record for the most cases – 51.61 per 1m (based on population estimates from Stats NZ).
While RSV is predominantly a winter virus, with very few cases, if any, reported in summer, it was kept at bay last year.
The lack of cases in 2020 – at most, there were 0.98 cases per 1m people mainly thanks to Covid-19 lockdowns and border controls – meant a significant portion of young children had no exposure to the virus, which could present like a common cold in milder cases. This resulted in a lower level of protective natural immunity across the country.
ESR public health physician Dr Sarah Jefferies explained this outbreak was more than two-fold greater than the historical average from 2014 to 2019 for this time of year. She described this activity as ‘‘unusually high’’, and thought the peak in cases was ‘‘possibly still to come’’.
While hospitalisations of children between 1 and 4 years decreased in the week ending July 11, RSV-positive hospitalisations were still much higher than the expected seasonal activity – more than 1.75 cases per 1000 per week.
Childcare facilities were also at the centre of many outbreaks, creating a breeding ground for the virus.