Health – Flu season and the influenza vaccine – expert Q and A

Following reports from the Northern Hemisphere that the latest season’s vaccine was not as effective as expected, the Science Media Cengtre has prepared a Q&A with influenza and immunisation experts ahead of the vaccine being made available in New Zealand.

Associate Professor Nikki Turner, director, Immunisation Advisory Centre; Department of General Practice and Primary Care, University of Auckland, comments:
There have been reports from the Northern Hemisphere that this season’s influenza vaccine hasn’t been very effective. What affects the vaccine’s effectiveness in individuals and across seasons?

“There was a flu strain of Type A flu (AH3N2) that we did see in the New Zealand season last year, though we fortunately still had quite a mild flu season. However, its effect was more prominent in Australia which had a very bad season and the same strain has been seen widely this Northern Hemisphere winter, creating a very heavy flu season.

The vaccine did not have a good match to that strain and it looks like vaccine effectiveness in the Northern Hemisphere has either been mediocre or not effective at all for certain groups with this strain.

“The vaccines arriving in New Zealand for our winter season have a new updated AH3N2 strain in them, which is a better match and we hope that will give better effectiveness. The government-subsidised vaccines for this season also are quadrivalent (two A strains and two B strains), which should give better protection than the traditional trivalent that have only one B strain in them.

“There is a further problem with flu vaccines – because there are lots of different strains of flu, an individual’s history of flu and of vaccination can affect their response to the current vaccine, either to boost immunity or in some examples to blunt the immune response. At times, therefore, a vaccine may not be effective to a strain or it may not be as effective as expected. The likely explanation for why at times we see blunting is the phenomenon called ‘original antigenic sin’ (prior exposure to a very similar antigen can lead to a sub-optimal immune response).”

Is it still a useful tool to help protect vulnerable people even when effectiveness is low? What are researchers investigating to improve the vaccine’s effectiveness?

“There are a range of other options to improve protection for people at high risk of flu. Firstly, there are new vaccines not yet available in New Zealand that are likely to be more effective in the elderly including those with a higher dose in them and those with an adjuvant, which is added to boost the immune response. We hope to see these available in the next year or two.

“For infants, we know that if a pregnant woman is vaccinated she passes antibody protection across the placenta and this offers very good protection to the infant for the first few months of life, hence vaccination in pregnancy is an important strategy. For elderly and those in poor health we can reduce spread of the disease to them by vaccinating frontline healthcare professionals, close family members and carers – called ring protection.

“Other countries are trialling ‘herd immunity’ approaches – they are vaccinating all children, particularly school children, to reduce the spread of flu across the whole community. Children are very effective spreaders of viruses so even with relatively low rates of vaccination this appears to be quite an effective strategy.

“Herd immunity does not require everyone to be vaccinated, the vaccinated will protect those around them who are unvaccinated. The UK, in particular, is trialling this strategy at the moment with a different sort of vaccine, a live attenuated vaccine delivered by a squirt up the nose.

Even with relatively low rates of immunisation coverage, it appears to be effectively reducing the spread of flu in the community. The advantage of this vaccine is that it does not require needles! This type of vaccine is not yet available in New Zealand, or anywhere in the Southern Hemisphere.

Dr Sarah Jefferies, Public Health Physician, Health Intelligence Group, ESR, comments:
What is the health burden of seasonal influenza in New Zealand?

“One of the challenges with influenza is that there is evidence that influenza infection does not always cause symptoms – so people may spread the virus without realising they are unwell. Research shows about one in four people may be infected with influenza during a moderate flu season, and the majority of those people may not know they have flu. This is one reason why immunisation is a key line of defence.

“The health burden of seasonal influenza in New Zealand varies from year to year, depending on: the types of flu viruses circulating and how well our populations are protected by the annual seasonal influenza vaccine as well as from immunity due to exposure to similar viruses in past seasons.

“For example, 2017 was a relatively low activity season for flu in New Zealand, with a peak of about 50 GP visits for influenza-like illness for every 100,000 people per week. This compares to the 2013 and 2015 seasons which were moderate seasons, with about 80 influenza-like illness cases per 100,000 people per week. In contrast, during the 2009 influenza pandemic, there was a peak of more than 250 cases per 100,000 people per week.

“People who become symptomatic with an influenza-like illness experience symptoms including high fever, cough, sore throat, muscle aches – it usually feels worse than and lasts longer than a cold.

How many people opt for immunisation?

“Over 1.2 million seasonal flu vaccinations were taken up by New Zealanders in 2017.”

How is it decided which influenza strains will be included in the seasonal vaccine? What strains are being included this year and why?

“Each year around September a panel of international experts at the World Health Organization (WHO) make recommendations for the components of the next year’s Southern Hemisphere seasonal influenza vaccine. They do this by reviewing the viruses which have been circulating in populations internationally and assessing how well different vaccine components perform against these viruses. The WHO also makes vaccine recommendations for the next Northern Hemisphere influenza season around February each year.

“Currently, there are four seasonal influenza viruses circulating globally – influenza A(H1N1), influenza A(H3N2), influenza B/Yamagata lineage and influenza B/Victoria lineage. The 2018 Southern Hemisphere seasonal influenza vaccine, therefore, aims to cover these four viruses by including the following inactivated virus strains:
• A(H1N1) – an A/Michigan/45/2015 (H1N1)pdm09 – like virus
• A(H3N2) – an A/Singapore/INFIMH-16-0019/2016 (H3N2) – like virus
• B/Yamagata lineage – a B/Phuket/3073/2013 – like virus
• B/Victoria lineage – a B/Brisbane/60/2008 – like virus.

“This year in New Zealand, the publically-funded influenza vaccine includes all four strains (i.e. it is a quadrivalent vaccine). There is also a non-publically funded vaccine which includes only the first three strains listed above (i.e. a trivalent vaccine) and this trivalent vaccine, therefore, offers a lower range of protection.”