25 September 2017, updated 1 November 2017
Influenza has been documented since January (inter-seasonal period), with the season beginning in May and a rapid rise in cases in early June 2017. A severe influenza season is continuing in Australia as of September, but with decreasing flu activity reported nationally towards the end of August and early September. The peak was in August (week 32).
The best way to evaluate the severity of an influenza season is to look at the dominant strain of flu (as some are more severe than others, as explained later), how early the season starts, the numbers of cases and deaths - and then compare these with previous years.
How are we tracking compared to last year?
More cases of flu: Influenza notifications observed in August 2017 were approximately 2.5 times higher than same period last year. Nationally, influenza surveillance reports indicated a total of 137,566 notifications as of 1st September (compared to 53,159 notifications received for the same period in 2016); with NSW (69,999) and QLD (35,360) reporting higher number of notifications to the National Notifiable Diseases Surveillance System (NNDSS) followed by SA and VIC. The highest age-specific notification rate was seen in older adults aged ≥80 years, followed by a secondary peak in children aged 5 -9 years old in the season to date. Flu activity varied across jurisdictions, and increased seasonal activity was notified in the country from June to August. The peak of the epidemic occurred around mid-August (weeks 32-33), which is a common timing for the peak of flu season.
Early season: The Australian influenza season in 2017 began earlier than 2016, with higher notifications compared to the average observed since early June. In the month of May (beginning of the season) and August (peak), the ratio of number of notifications were 2.1 and 1.5 times higher respectively, compared to past 5-year average in the same months.
The worst kind of flu, H3N2: Of seasonal influenza, influenza A results in the most complications and fatalities, and of A strains, H3N2 is the most severe. A notable exception is the H1N1pdm09, of which a distinct lineage in South Asia has been causing severe disease and an apparent case fatality rate of 6% or higher. H3N2 has been the dominant strain in 2017, and is associated with the most severe seasonal epidemics, often with paediatric deaths. Of circulating flu viruses 69% were influenza A virus (majority A/H3N2), followed by influenza B (31%). Influenza A has comprised 63-83% of all cases, varying by State, and influenza B up to 30%. H3N2 is the strain that can result in previously healthy children and adults dying of influenza. Deaths have been reported in a child and healthy adults in 2017, and severe infection in a pregnant woman along with a large number of deaths of elderly people. Past severe H3N2 epidemics, which featured deaths in healthy children, include the 2003, 2007 and 2012 seasons.
Nursing home outbreaks: The 2017 epidemic has featured severe outbreaks in aged care facilities, in several states. Surveillance reports indicated that influenza outbreaks in institutions in NSW were 4.2 times higher than the past 5-year average. Severe outbreaks have occurred in residential aged care facilities. This has prompted calls for mandatory influenza vaccination for workers in aged care.
Workers in healthcare, aged care and childcare can be a source of transmission of infectious diseases to vulnerable people in their care and to other staff. Immunisation is recommended for these occupational groups to prevent transmission of vaccine preventable diseases. The annual influenza immunisation rate in Australian HCWs varies widely, and ranges 22-70%, but mostly is low. There are few data on vaccination rates in aged care workers, but rates are lower. Mandating vaccination of ACF workers would be an international precedent. The NSW Ministry of Health introduced mandated health worker vaccination in 2007, with revision of the policy in 2011, but influenza vaccination was not included in this legislation, and remained recommended but not compulsory.
A mandated policy in aged care should be considered along with the healthcare and childcare settings, and should be informed by research and surveillance data from these settings. Such a policy should also be systematically evaluated after implementation for effectiveness.
So how bad is 2017? Unpacking the data: We can judge severity by the dominant strain, the pattern of deaths and hospitalisations, as well as intensive care (ICU) admissions. H3N2 is the dominant strain, so that's bad news. The picture is otherwise mixed, with some indicators of severity.
While total notified cases are higher, intensive care admissions and estimated population mortality (pneumonia and influenza) rates are lower than 2016. Since April 2017, there were higher numbers of hospital admissions (2,020) but lower ICU admissions (166, 8.2%) compared to last year. A total of 72 influenza-associated deaths were reported to the notifiable diseases system (NNDSS) for the year till September 1, including 1 child death, and this compares to 33 deaths in 2016 for the same period. From NSW, the estimated rate of deaths from influenza and pneumonia is 1.9/100,000 NSW population, which is lower than the peak in 2016.
The total number of cases may be higher because of new testing practices across jurisdictions, and introduction of rapid testing in NSW hospitals. Rapid influenza diagnostic testing is useful in decision making for treatment purposes, but has limitations with test sensitivity compared to other standard methods of testing such as using RT-PCR, serology or culture. Historically, more testing for influenza is conducted in Queensland, and there are differences in testing policies in paediatric hospitals between states, which could also bias surveillance data. There has been a backlog of specimen processing from Victoria, so the final epidemic pattern may vary. The epidemic pattern needs to be analysed, accounting for these variations in testing practices in the country.
There are some discrepancies such as higher notified deaths in the NNDSS data compared to 2016, but a lower estimated rate of death from influenza and pneumonia, as well as lower admission rates to ICU. The relative morbidity and mortality impact needs to be determined.
There have been a number of serious and fatal outbreaks in aged care facilities (ACF) in 2017. A total of 461 outbreaks occurred in institutions as of 10 September in NSW alone, the majority due to influenza A. Among those affected in aged-care facilities, 533 people (9.6%) required hospitalisation among the residents reported with ILI during the year to date, and 215 deaths occurred in people with significant other comorbidities. To date, 94 deaths were reported in aged-care facilities in Victoria, and also a number of influenza-related deaths were reported in aged-care facility outbreaks in Tasmania. These fatality numbers are higher than the total deaths reported to the NNDSS, which illustrates that different systems give you different information, and it is important to look at all sources of data for an overall picture.
So, in summary, this shows a mixed picture – the most severe seasonal strain, severe nursing home outbreaks, deaths in healthy younger people, but lower rates of intensive care admission and morbidity compared to 2016.
Other vulnerable populations
In addition to the elderly, we know that certain risk groups such as people with chronic diseases, Aboriginal and Torres Strait Islanders, pregnant women and those with low immunity are at greater risk of flu and serious complications. It is important to evaluate the impact of the 2017 epidemic in these groups and ensure optimal vaccination rates are achieved. Vaccination rates for Aboriginal and Torres Strait Islander people are not as high as they could be, and vaccination may also be delayed due to lack of access to immunisation services and other barriers.
Is the vaccine working? The 2017 Australian Influenza Vaccine contained:
• A/Michigan/45/2015, (H1N1) pdm09-like virus;
• A/Hong Kong/4801/2014, (H3N2)-like virus;
• B/Brisbane/60/2008-like virus, Victoria lineage;
• B/Phuket/3073/2013-like virus, Yamagata lineage.
Influenza vaccine is generally effective. Whether the vaccine works well in a particular season is determined by the match of the vaccine strains to the circulating seasonal strains, and on the immunogenicity of the vaccine, which varies by age group and medical risk factors. Cold chain failures may also result in loss of vaccine effectiveness.
Vaccine match: Media reports suggest poor vaccine match. However, the influenza B match is good, given less genetic diversity in B strains compared to influenza A. The match of the A strains is moderate to low, but field effectiveness particularly against H3N2, needs to be determined. So far, moderate match with circulating strains and vaccine viruses have been reported for the season in 2017 in the country. However, a number of reports in the media suggest “rapid mutation”, infection in vaccinated elderly, and poor match. There was evidence of some drift from the A H3N2 Hong Kong strain in the vaccine in the UK in their last season. A study published on October 26th 2017 showed that the overall vaccine effectiveness, as measured in Victoria, was 33%, and only 10% for H3N2, confirming the earlier observation of poor vaccine effectiveness. It is important to understand the difference between vaccine match and other factors that can affect vaccine effectiveness, such immunosenescence in the elderly. Even an incompletely matched vaccine can protect the vulnerable during a nursing home outbreak, so vaccination is always worthwhile.
Vaccine effectiveness: Media reports suggest poor vaccine match and cite cases of influenza in vaccinated elderly people. It should be noted, however, that explosive outbreaks of influenza in highly vaccinated aged care facility populations have been well documented in the past, and may reflect intensity of transmission within the closed setting of ACF, as well as lower immunity and immunosenescence in the frail elderly. After the age of 50, the immune system declines in a predictable fashion, making all vaccines less effective with increasing age. This could explain the observation that some elderly people who were vaccinated still contracted influenza. However, even if you get flu after vaccination, the vaccine will protect against severe illness and death. Field vaccine effectiveness for the season in 2017 from one study suggests 33% effectiveness overall, lower for H3N2 (10%) - see above. Further field-testing of vaccine effectiveness is required, using methods such as the screening method, test-negative case design or within an outbreak setting. We have shown previously how to calculate effectiveness of the vaccine during an nursing home outbreak. Once this is calculated, it is a matter of working out how much of infections occurring in vaccinated elderly is explained by immunosenescence and intensified transmission within aged care facilities, as opposed to true vaccine mismatch. However, even a vaccine of low effectiveness can have public health impact because the disease burden is high.
Antiviral supply and resistance: During severe flu seasons, demand for antivirals increases, and a shortage of drugs due to increased demand was reported in the season. Circulating strains were largely sensitive to NAIs.
Facts about flu
What are the symptoms? Common clinical symptoms for both influenza A and B may present with sudeen onset of fever, cough, sore throat, myalgia/myositis, fatigue, and gastrointestinal (GI) presentations such as vomiting and diarrhoea. Fever is more common in children than adults. Although clinical presentations are indistinguishable between influenza A and B infections, some studies report of differences by age groups. Influenza A tends to cause more severe illness, although influenza B can be severe in children. In adults, influenza B infections more frequently present with vomiting, diarrhoea, abdominal pain, headache, general weakness and rhinorrhoea compared to influenza A. It was found that cases with influenza B infection presented more with upper respiratory tract infections, myosotis and gastroenteritis compared to influenza A in children. Without a test, however, you cannot prove influenza infection, as there are over 90 other cold and cough viruses which circulate in winter. However, when an epidemic of flu is occurring, a flu-like illness is more likely to be flu.
How does it spread? Influenza infection can be transmitted through droplets, aerosol and direct contact with infected person. Whilst droplet is the main mode of spread, numerous studies have documented airborne transmission. In one US study, viable influenza virus was detected in the air of the emergency department 3 hours after the infected patient had left.
Who is affected? Influenza infects all ages, with peaks at the extremes of age – the very old and the very young. In 2017 the peak has been in older adults >80 years and over and children 5-9 years. Males and females are equally affected. Up to a quarter of people can get infected in a severe epidemic.
What are the complications? Influenza can result in primary viral pneumonia, which occurs early in the course of illness, or secondary bacterial pneumonia, with onset later (1-2 weeks after initial symptoms). Bacterial pneumonia is the most common influenza-associated complication, especially in children and the elderly. Bacterial infection can be complicated by antibiotic resistance and there is are vaccines available for the most common bacterial complication, pneumococcal infection. Unfortunately, despite being provided free to people over 65 years and other risk groups, rates of vaccination against pneumonia are low. Other complications can be worsening of asthma and respiratory diseases and exacerbation of underlying comorbidities in persons who are at-risk of the infection. Heart failure, precipitation of heart attacks and sinusitis may also occur. Occasionally encephalitis and complications of other organ systems may occur.
Influenza vaccine: Primary prevention is with vaccination with influenza vaccine annually. The mutation of the virus year to year requires annual vaccination. The vaccine is safe and effective, but effectiveness can very depending on how well the vaccine is matched to circulating strains. People aged 65 years and over, and those with medical or other risk factors are recommended and funded for free vaccine in Australia. The quadrivalent vaccine, introduced in 2016, allows protection against four strains, which gives better effectiveness against flu. Research is underway for a universal flu vaccine which will remove the need for an annual jab.
Other prevention & control measures: Neuraminidase inhibitors (NAIs) can be used as prophylaxis or treatment, and when used as prophylaxis can curtail outbreaks. Cough etiquette, hand hygiene and infection control measures are also vital to prevent further spread of infection. Personal protective equipment such as masks are recommended for healthcare workers. Guidelines recommend “droplet precautions” for seasonal influenza, however, airborne transmission is well documented for influenza.
NAIs are recommended for prophylaxis and treatment of influenza infection, and are most effective if they are taken within 48 hours after the onset of illness. Antivirals can reduce severe complications of influenza infection and can also shorten the duration of illness. They are also proven to mitigate severe, hospitalised cases of influenza, and should be given even after the 48 hours window (up to 72 hours) for patients in intensive care.
Recently ECDC expert opinion also confirmed the use of NAIs in prevention and treatment of severe influenza during seasonal flu outbreaks, pandemic and zoonotic outbreaks with susceptible influenza viruses, and reported that stockpiling of NAIs should be considered in preparedness plan during the flu outbreaks. The circulating strains of influenza in 2017 were largely sensitive to NAIs.
Antibiotics are available to treat bacterial secondary infections complicating influenza, and it is important to test for bacterial secondary infection in hospitalised patients, even if the testing for flu is positive. Pneumococcal vaccine is also important as a preventive measure against pneumonia.
Novel vaccination approaches for the elderly: Immunosenescence is a predictable decline in immunity, which begins around the age of 50 and continues in an exponential fashion with age. This results in lower immunogenicity of all vaccines in older people. Strategies such as novel adjuvants, intradermal vaccination and high dose vaccines could improve immunogenicity in the frail elderly. A study from the United States has shown the effectiveness of high-dose influenza vaccine in adults aged 65 years and over, with approximately 36% reduction of influenza-related mortality in the study during the season where A/H3N2 was in circulation. In aged care, there has been discussion of high dose influenza vaccine as a solution to overcoming immunosenescence. However, until such alternatives are available, vaccinating with the available seasonal vaccine is important, as protection has been demonstrated in aged care even with an incomplete vaccine match.
We have seen a severe influenza season in 2017, with H3N2 being the major strain. As influenza infection is unpredictable in nature, tools to assist with planning health care services would inform surge capacity planning. Real-time data are also needed to understand the impact on vulnerable populations, especially Aboriginal and Torres Strait Islander people. Very low vaccine effectiveness was observed against H3N2. Solutions to improve vaccination effectiveness in frail elderly people, such as high dose vaccines, novel adjuvants or intradermal vaccination, need to be pursued. We also need to ensure high rates of occupational vaccination in people who care for vulnerable people in institutions such as hospitals, child care and aged care. Antivirals can be used as prophylaxis to control serious epidemics in aged care, but better surveillance in aged care and the ability to detect outbreaks rapidly will help. Finally, given that bacterial infection is a common cause of death and serious illness following influenza, low rates of pneumococcal vaccination in the elderly must be a focus for improvement.
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