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Flu season and the influenza vaccine

Flu season and the influenza vaccine
- Expert Q&A
28 February 2018

Following reports from the Northern Hemisphere that the latest season's vaccine was not as effective as expected, the SMC prepared a Q&A with influenza and immunisation experts ahead of the vaccine being made available here.

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.

"Vaccine effectiveness is difficult to accurately predict season-to-season and person-to-person. We know overall that when the vaccine types more closely match the circulating strains the vaccine is likely to be more effective. Each year, for the northern and southern hemisphere, there are meetings to decide what is the best prediction for circulating strains and therefore what is the best choice for the seasonal vaccine.

"However, other factors also make a difference to effectiveness. Older people, infants, and people with a range of underlying chronic conditions do not create such a vigorous immune response, whereas children and healthy adults create a more vigorous response. However, those who are most at risk of severe flu and its complications are those who are less likely to mount a strong immune response, so we cannot guarantee that even when they are vaccinated they are well protected.

"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.

"I have been misunderstood recently, particularly in the anti-immunisation social media, as implying this is mandatory vaccination, but it is not. 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.

"Finally, alongside vaccination, remember basic public health principles – don’t spread your bugs. Stay home when you are sick, keep social distance from others and cover your mouth when you cough. This will reduce the spread of flu significantly, however, it will not entirely eliminate it as we know people can carry flu virus and not actually be sick, so vaccination remains important alongside this.

"The holy grail of flu vaccines is to create a vaccine that will cover all strains and so won’t need to be changed every season – the world is working hard on this one but we are still quite a few years away. So in the meantime, we are stuck with imperfect vaccines that are still important to use against such a nasty and common virus.

The other future hope is NO NEEDLES – new delivery mechanisms, and in particular MAPS (microarray patches) that you stick on the skin and use microneedles to enter across the skin barrier. That will help our needle phobia no end."
________________________________________
Dr Sarah Jefferies, Public Health Physician, Health Intelligence Group, ESR, comments:


What is the health burden of seasonal influenza in New Zealand? How many people get ill every year and how many die?

"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."

Seasonal activity

"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.

"About half of people with influenza-like illness may have influenza infection confirmed through testing during a normal flu season."

Illness severity

"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.

"However, certain groups of people are at more risk of severe complications of flu, such as pneumonia, which is why the seasonal influenza vaccine is free for pregnant women, older people and those with certain medical conditions. The flu can also make normally healthy and young people very sick, sometimes causing hospitalisation and possibly death, so it is important to avoid the spread of the flu by good hygiene measures (as described on the Ministry of Health website, like covering coughs and sneezes, and washing and drying hands thoroughly) and to access preventative measures like the seasonal influenza vaccination.

"It is difficult to determine the exact numbers of deaths each season which are due to flu. This is because influenza virus infection may be one of many factors contributing to a person’s death. The SHIVERS project monitors Severe Acute Respiratory Illness (SARI) Intensive Care Unit (ICU) admissions and associated deaths in Auckland hospitals as an indication of influenza season severity.

"The numbers hospitalised each year varies, but as an example, 2017 was a moderate year for indicators of flu severity: with a peak of about 250 influenza-related hospitalisations per week in July; and about two influenza-related ICU admissions per 100,000 people in Auckland and Counties Manukau DHBs reported through the SHIVERS project. The highest rates of hospitalisation were recorded in older people and babies less than 1 year old."

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."

There have been reports from the Northern Hemisphere's flu season that the vaccine has been less effective than anticipated. Is this the case, if so, why might that be? Does it have any implications for New Zealand's upcoming season?

"The Northern Hemisphere has been reporting moderate to high levels of influenza and influenza-like illness activity during their 2017/18 season. The effectiveness of their Northern Hemisphere seasonal influenza vaccine is yet to be finally determined in most countries. However, there are a few reasons why there may be a higher burden of flu than in recent years and a poorer vaccine match there:
• Virus mutation: The influenza virus can rapidly change as it spreads through the population – this means some strains of virus may not be recognised by the body’s immune system in people who are vaccinated or have been previously exposed to the virus. Influenza A(H3N2) is notorious for being able to rapidly change genetically, and this is the type of seasonal virus currently being commonly detected in parts of the Northern Hemisphere. However, it is important to note that the current Northern Hemisphere seasonal vaccine contains some different components to what is included in our Southern Hemisphere 2018 vaccine. The WHO recommended a change in our Southern Hemisphere seasonal influenza vaccine for 2018 which better covers some strains of influenza detected in the 2017 Southern Hemisphere season and the Northern Hemisphere 2017/18 season so far.

• Susceptibility in vulnerable groups: A higher proportion of older people tend to be more adversely affected by influenza A(H3N2) – this group tend to have a poorer immune response to vaccination.
"It is difficult to predict exactly what strains of seasonal virus will end up circulating in our 2018 season. The health impact will depend on:
1. How well New Zealanders use preventative measures like immunisation and good hygiene practices (see the Ministry of Health website for best recommendations);
2. 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).
"A good source of further information about immunisation is the Freephone number in New Zealand (0800 IMMUNE) and the Ministry of Health website."

ends

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