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June 2019 | Published by RCPA

Issue #092

Influenza 2019 – Professor David Smith

Influenza 2019 – Professor David Smith

With many reporting that this year is a “killer” flu season, we spoke to Clinical Professor David Smith, Clinical Microbiologist/Virologist in the Division of Microbiology, and Director of the National Influenza Centre at PathWest QEII Medical Centre, to discuss if and why the 2019 flu season has been particularly bad, and what we can do to prevent the spread of infection.

“Influenza is notoriously difficult to predict. The 2019 season has started badly with a high number of cases and many people seeking medical treatment, going to hospital or dying. We saw that the season started earlier than usual with a high circulation of two viruses which are causing problems; an influenza A/H3N2 strain and an influenza B strain. However, we won’t really know how bad the season will be until later when we know how big the peak of the season is and how long it lasts.

“On average between 10-30% of the population will get infected and around 2,500 people will die due to influenza infection each year, most of whom will be aged 65 or over. It is important that people get vaccinated each year before the influenza season starts.  We can’t be sure whether a season is going to be mild, moderate or severe, so if people wait until we know how bad it is going to be, then their vaccination will be too late to give them protection throughout the season.  So just go and get vaccinated every year!”

Influenza virus is a respiratory virus, meaning it mainly causes infections involving the lungs, airways, nose and throat. Infections are usually mild, however high fevers, aches and pains, cough, and a sore throat are common, and people are often off work or school for a few days. Sometimes, and especially in pregnant women, young children, older people and people with chronic illness, the virus causes pneumonia. Rarely, it can also spread to involve the heart, brain or muscles. Influenza infection also increases the likelihood of bacterial infections, ranging from middle ear and sinus infections, right through to fatal bacterial pneumonia.

There are two main types of influenza viruses that cause infections each year; influenza A and influenza B, both of which are found worldwide. Influenza A is the most serious of these and is found in both humans and animals, though the human and animal subtypes are different. It is also the type that causes pandemics when a completely new subtype spreads from animals to humans and adapts to become a human strain. The influenza A/H1N1, influenza A/H3N2 and influenza B viruses that are currently circulating in humans continually change their surface proteins, so they are not affected by the protection we have built up from previous infections or vaccinations. This is why we can get multiple infections in our lifetime, why the vaccine has to be changed each year, and why we have to get the vaccine every year.

“There has been a lot of discussion about why it is likely that this year will be a severe season, and whether or not this is linked to last year’s mild winter season, or the increase in influenza cases across the summer. The thinking behind this is that because there was so little influenza last year, very few people got a boost to their immunity from being exposed to influenza. This idea, however, needs some research to prove that is the case, which would be valuable in getting a better understanding of the virus and its prevention.

“The single best preventive measure against influenza is to get vaccinated 1-2 months before the beginning of the season. Everyone will benefit from vaccination, but it is particularly important in those who are at high risk of severe influenza. These include pregnant women, anyone aged 65 years or over (even if they are healthy), aboriginal and Torres Strait Islander populations aged 15 years or over, children under 5 years-old,  and people with any chronic illnesses including heart disease, respiratory disease, diabetes, neurological diseases or any other illness requiring regular doctor visits or admission to hospital; the very obese; and people with a poor immune system due to a disease or treatments that depresses the immune response.

“Vaccination of pregnant women is particularly important not just to protect the mother and baby while it is still in the uterus, but also to protect the baby in the first few months of life. They rely on antibodies that have crossed the placenta from the mother to protect them. Of course, good personal hygiene practices are always recommended to help reduce your risk of getting or spreading influenza and other respiratory viruses.

“Influenza imposes a huge health, social and economic burden on communities each year, and those who choose not to be vaccinated magnify that burden. There is the obvious personal health risk of being unvaccinated, especially those who are vulnerable to severe influenza, but also the lost work time and income, caring for sick children, and also exposing others to influenza. Vaccination reduces the number of people attending medical practices and Emergency Departments, and preserves that capacity for those that need it. The vaccination is safe and there are very few scientifically valid reasons for people not to get vaccinated.”

If a doctor is confident that influenza is present, then testing may not be necessary. Otherwise, influenza is usually diagnosed by taking swabs from inside the nose on both sides, and from the back of the throat. For young children and people who are in hospital, other samples may also be collected.

“Most testing is now done through methods which detect the genetic material of the virus and show which influenza type is present. Those results usually take a few days to come back, so your doctor will decide on the best treatment before those results are available. Antiviral drugs are now available, the commonest of which is a tablet called oseltamivir which can reduce the illness and lower the risk of complications like middle ear infections and pneumonia. However, this needs to be started as soon as possible, and no later than 48 hours after symptoms begin.”

If testing is done, we use the information about the specific influenza virus to assist treatment decisions and to determine the risk of spreading the infection. This information will also be used to assess how effective the vaccination program has been. A selection of these viruses is also sent to the World Health Organization laboratories where they are analysed, and the information is used to select strains for future vaccines.

 

 

 


 

 

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