2019 - the Flu season that was

3 October

ESR has called an end to its annual flu surveillance with indicators for influenza and influenza like illness (ILI) having dropped below baseline figures for the last two months.

The 2019 influenza season hit a peak much earlier than recent seasons with earlier activity than usual detected in both community and hospital based surveillance systems.

Public Health Physician Sarah Jefferies says GP consultations for flu-like illness increased to seasonal levels at the end of May, peaked late in June and then declined to below the baseline level at the end of July.

Dr Jefferies says the pattern of flu in New Zealand was similar to Australia, which had an early start to the influenza season after higher than usual activity at the start of the year, and with declining numbers following a peak in July.

While the New Zealand influenza season started earlier, she says the overall community influenza activity remained within expected levels throughout the season.

“When comparing New Zealand’s current community influenza rates with the past few years, we saw similar levels to those seen in 2017, but higher than usual rates seen in both 2016 and 2018, which were particularly low years for influenza activity.”

As well as an early start to the influenza season, Dr Jefferies says ESR surveillance showed a higher than average percentage of samples testing positive for influenza viruses.

“This indicated that a greater than usual proportion of respiratory virus in the early part of the winter was due to influenza rather than other common respiratory viruses such as rhinovirus and respiratory syncytial virus.”

ESR maintains a number of surveillance systems on behalf of the Ministry of Health to provide a timely and comprehensive understanding of influenza like illness activity and severity in New Zealand.

Dr Jefferies says ESR's public health and virology experts characterise respiratory viruses, assess the effectiveness of the seasonal vaccine, and synthesise influenza surveillance data into the weekly online flu surveillance dashboard and intelligence report.

Two viruses were mostly in circulation for the 2019 season, influenza A(H3N2) and influenza B/Victoria. Influenza A(H3N2) viruses often cause more illness in elderly populations, whereas influenza B viruses often affect younger and school aged children relatively more.

Testing showed that seasonal influenza vaccine viruses were a good match overall to those influenza viruses circulating in New Zealand. However, during the season there was a change in the influenza B/Victoria virus strain circulating in New Zealand which may have impacted on the effectiveness of the vaccine against this strain.

“Tracking the flu relies on a range of data streams which help build our understanding of the national picture. There are multiple factors which influence flu transmission, such as virus mutation, and how well different groups of people are protected by measures like seasonal flu vaccination, which makes predicting the trajectory of flu activity during a season challenging”

Information from ESR’s surveillance helps the Ministry of Health, the District Health Boards, and the wider health sector prepare for seasonal flu, influenza pandemics, and the emergence of novel viruses such as SARS or MERS.

Planning is already underway for the next influenza season with information from New Zealand’s surveillance systems used to help inform decisions on which influenza vaccines will be used in 2020.

Close to 1.38 million doses of flu vaccines were used in New Zealand in the past year.

The last ESR weekly report is here. https://surv.esr.cri.nz/PDF_surveillance/Virology/FluWeekRpt/2017/MoH_Influenza_Report/MoHInfluenzaRpt201739.pdf

Interactive dashboard is here. https://www.esr.cri.nz/our-services/consultancy/flu-surveillance-and-research/

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