May 9, 2021

Maori News & Indigenous Views

New study out on H1N1

5 min read

A major new scientific study, estimates that 1.26 million or 29% of New Zealanders were immune to the pandemic influenza virus by March this year. But a large proportion of the population remain vulnerable.

Since the testing was completed many New Zealanders have also been immunised against pandemic influenza, however, given that there is still a large proportion of the population at risk from infection this winter, both influenza immunisation and basic measures to stop the spread of influenza remain important.

The Ministry commissioned study, conducted by ESR, estimates that of the 1.26 million people, about 480,000 people had some immunity prior to last year’s pandemic wave, mostly in the older age groups. An additional 780,000 were estimated to have been infected during 2009. The highest rate of infection during 2009 was in school age children – where one in three children were affected. Almost half of those infected showed no obvious symptoms.

ESR’s national influenza centre head, Dr Sue Huang, said the rate of pandemic influenza A H1N1 infection during 2009 varied greatly by age – with the most surprising finding of the study being how many young people were affected.

The high rate of transmission and infection among school-aged children was about ten times higher than we initially estimated based on clinical surveillance.

“This study confirms that the Pandemic Influenza is able to spread rapidly through communities. One of the more interesting findings was that it was a sub-clinical illness (i.e. no symptoms) for almost half of those who were affected. For most people their symptoms were mild, however, for many it was a very serious illness requiring an admission to intensive care,” Dr Huang said.

Deputy Director of Public Health, Dr Darren Hunt thanked all those who had agreed to take part in the post-pandemic survey by agreeing to have a blood test.

“This information is invaluable for our understanding of the virus, and our pandemic planning.”

“As we go into winter, it is also important to remember that the virus has not gone away. While the level of influenza activity in New Zealand remains relatively low at the moment, there is still circulation of the pandemic influenza H1N1 virus and other respiratory viruses in the community.

There have been 12 confirmed cases this year to date, including one admitted to ICU.

We can all help reduce the spread of influenza and colds by washing and drying hands frequently, covering coughs and sneezes, and staying home from work or school if you are sick. Also, if you or your family are ill and you are concerned, or if your condition worsens, get health advice early by calling your GP or Healthline on 0800 611 116.”

Influenza immunisation is especially recommended for those at greatest risk of complications from pandemic influenza, including women who are pregnant or recently pregnant, very young children, severely overweight people and those with underlying medical conditions. Immunisation is free for eligible groups only until 30 June.

If you haven’t yet been immunised, it’s important to get the vaccine as early as possible, as it takes a up to a fortnight for the vaccine to offer its full level of protection. Young children also need a longer time as they require two doses a month apart to be assured of best protection.

Weekly consultation rates for influenza-like illness in New Zealand, 2008-2010

Week 21: 24 – 30 May 2010

Note: the graph excludes Counties Manukau data due to consistency issues currently being resolved.
Source: Institute of Environmental Science and Research, Influenza Weekly Update 2010/21

The international picture

As reported by WHO on 1 June 2010, the most active areas of pandemic virus transmission are in parts of the Carribean and Southeast Asia where low level circulation is occurring. There is little evidence of pandemic influenza activity inthe temperate zone of the southern hemisphere.

The WHO is continuing to actively monitor the progress of the pandemic.
For the WHO’s latest updates on the global pandemic, check their website:

The WHO Director-General has also issued a statement on 3rd June following the eighth meeting of the Emergency Committee. Following the advice of the Emergency Committee, the Director-General determined that while the period of most intense pandemic activity has passed, pandemic disease is expected to continue to occur and that a further meeting of the Emergency Committee to reassess the epidemiological situation would be convened by mid July 2010, when information from the winter influenza season in the Southern Hemisphere will be available. Committee members stressed that it remains critical for countries to continue to maintain vigilance concerning the pandemic, including all necessary public health measures for disease control as well as influenza virus and disease surveillance.


Seroprevalence of the 2009 influenza A (H1N1) pandemic in New Zealand. May 2010

The ESR study looked at blood samples taken both before and after the 2009 influenza season, to determine the proportion of people affected during the pandemic. The full study is available on the Ministry of Health website Sampling of 1696 people has allowed estimates of exposure and immunity to be calculated for the New Zealand population.

The study showed that the pandemic virus was highly infectious and reached a large proportion of the population in a short time frame. This has resulted in higher-than-expected levels of immunity in the community.

Infection rates varied with ethnicity. The highest immunity was measured in Pacific Peoples (49.5%) followed by Maori (36.3%). This may in part be due to these populations having a higher proportion of young people.

The study shows that males and females were affected in equal numbers in 2009, and that health care workers had about the same chance as anyone else of catching pandemic influenza during 2009.

The pandemic influenza strain was newly identified in 2009. However 11.2% of people were shown to have pre-existing immunity which protected them from the new pandemic strain. This pre-existing immunity was most common among retirement-age adults (22.6%). By contrast, this pre-existing immunity was much less common in children and working-age adults.

The study also confirmed that influenza was mild for most people who contracted the virus, however we know that for some people pandemic influenza caused a serious illness. Over 1,000 people needed to be hospitalised last year and so far 35 deaths have been attributed to pandemic influenza.

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