ESR scientists are reiterating that this year’s flu vaccine has been updated to include the H3N2 strain linked to increased flu hospitalisations and deaths in the northern winter.
But experts from the environmental health agency also add that the challenge for scientists and medical authorities is that the Influenza A (H3N2) strain is ‘notorious’ for being able to rapidly change.
New Zealand hospitals and general practices are gearing up for what is likely to be a tough winter after reports of a severe flu season in the northern hemisphere and much higher than usual hospital presentations over the New Zealand summer.
Dr Sarah Jefferies the Public Health Physician for the environmental health agency ESR, said WHO recommended a change in the Southern Hemisphere seasonal influenza vaccine for 2018 to better cover some strains of the influenza detected in the 2018-18 northern hemisphere season as well as strains detected last winter in the southern hemisphere.
The UK’s Public Health England has reported that the 2017-18 flu season put the most pressure on GPs since the 2010-11 winter and led to very high admission rates to hospital and intensive care services and a much higher mortality rate – with 364 flu-related deaths reported as at mid-April.
And while most of New Zealand had a mild flu season last winter Australia had the biggest flu season since the swine flu pandemic of 2009. Australia’s Department of Health reported that though the predominant influenza A(H3N2 infection was not more severe than usual there were higher deaths due to a high numbers of people effected as the vaccine effectiveness was low for the strain of influenza A(H3N2) that circulated in Australia last winter.
For the first time this year New Zealand’s publicly-funded flu vaccine is a quadrivalent vaccine so is covering all four major seasonal influenza viruses circulating globally and not just three. The viruses covered are influenza A(H1N1), influenza A(H3N2), influenza B/Yamagata lineage and influenza B/Victoria lineage but Jefferies said rapid mutations can always mean that some strains of the virus may not be recognised by the immune system of people who have been vaccinated or exposed to that ‘flu virus
Jefferies, said countries such as the UK reported moderate to high levels of influenza and influenza-like illness during their 2017/18 season but said it was important to note that the Southern Hemisphere vaccine had been updated to reflect this.
However, she said it was difficult to predict exactly what strains of seasonal virus would end up circulating in New Zealand’s 2018 season.
“The health impacts of flu this year will depend on how well New Zealanders use preventative measures like immunisation and good hygiene practices, how the strains which circulate compare to viruses we’ve had previously, which cause natural immunity, and to the strains in the vaccine, which also generate immunity.”
She said the best option for prevention was immunisation, and the vaccine was free for older people, pregnant women and those with certain medical conditions. The flu vaccination is also free for under-18 year olds in the quake-effected Hurunui and Kaikoura districts of north Canterbury.
Timing of vaccine
Associate Professor Nikki Turner, director of the Immunisation Advisory Centre (IMAC), recommended in an article in the New Zealand Herald in early April that people with poorer immune systems hold off until May to get their flu vaccine so their immunity didn’t wane before the full season hits
She said it takes two weeks from people getting their flu vaccine to become immune and the flu season normally starts in June or July.
“People whose systems are not so vigorous – the elderly, or people with medical conditions – it might be better for them to get it in May rather than April,” Turner said last month.
“For healthy people who have a good immune response, getting the shot any time is fine.”
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