The H3N2 virus

Australian flu, first case in Italy: symptoms and duration. Expected increase in encephalitis

He was admitted to infectivology at the San Martino General Hospital in Genoa. This is a 76-year-old gentleman with a challenging clinical picture and important symptoms

by Redaction Rome

4 November 2024

7' min read

Key points

influenza virus A-H3N2
Three symptoms to recognise the virus
How to distinguish Covid and influence
The first case of H3N2
Lopalco: virus always bad, the more we study it the more dangerous we see it
Ciccozzi: real problem will be increased cases with Jubilee
Simit: "expected increase in encephalitis with Australian flu"
The beginning of the flu season
Symptoms

7' min read

The flu season in Italy is shaping up to be a heavy one, with the first cases of the 'Australian' variant already reported in some regions such as Lombardy, Piedmont and Lazio. It is caused by the H3N2 subtype of the influenza A strain, a more virulent and aggressive variant than the H1N1 that dominated the flu season last year. Symptoms are more severe in both the respiratory and pulmonary tracts, with the possibility of also affecting the brain. Rare cases, but already encountered, as reported by infectivologist Matteo Bassetti regarding a 76-year-old patient admitted to the San Martino General Hospital in Genoa with important symptoms also at a neurological level.

The influenza virus A-H3N2

Talking about the flu season ahead of us is virologist Fabrizio Pregliasco: 'We expect a fairly brisk flu season precisely because of the presence, already identified, of this variant of the influenza A-H3N2 virus, which is immunoevasive, new, and has a high capacity for spreading. The unfortunate thing is, as we have already seen in some cases, that this variant is heavier in its effects on health than other influenza viruses and can also have neurological involvement. It is very rare, but this possibility in fragile and at-risk persons is there. So a more intense manifestation, with heavier cardiac and respiratory effects,' Pregliasco explains. Difficult, at the moment, to predict which variant will prevail this year, whether H1N1 or H3N2. Certainly the peak will be reached with the arrival of the more intense and prolonged cold, 'and it is never wrong to say that it will be around the holidays, which, with kisses and hugs, will also play into the hands of the viruses,' the expert emphasises.

Three symptoms to recognise the virus

'The real flu,' Pregliasco explains, 'can be recognised by three things: an abrupt rise in body temperature, with fever over 38°, the presence of muscle and joint pain, and respiratory symptoms, i.e. a stuffy or runny nose'. Unlike influenza, 'Covid, on the other hand, can do anything, going from very heavy to nothing: that is its strength. Right now we have a cycle for Covid that is independent of the season, with waves every four to six months like those caused by a 'pond stone'. There was an upswing in July and there is an upswing now, with a new XBB variant somehow coming back in, mixing things up'.

How to distinguish Covid and influenza

In order to distinguish between the two diseases, the expert's indication is the Covid test for the elderly and frail, because this category, if affected by Covid, can benefit from an antiviral drug on the judgement of the treating doctor'. For all the others, whether Covid or influenza, on the other hand, the advice is 'responsible self-medication with anti-inflammatories and if things do not improve after two or three days, contact the doctor, without taking antibiotics from the start'. The call for vaccination remains firm: 'The flu vaccine - which also covers the H3N2 variant - is an opportunity for everyone, because even in a young person catching the flu creates 5-6 days of blockage. For those who are more fragile or for the elderly,' concludes the virologist, 'pairing it with the anti-Covid vaccine is recommended, because this covers a virus that, although less 'bad', still causes 100 deaths a week'.

The first case of H3N2

The first ever case of influenza virus H3N2 was certified in Genoa with an admission to infectivology at the Policlinico San Martino. "It is a 76-year-old gentleman with a challenging clinical picture and important symptoms". Reporting this in a post on X was Matteo Bassetti, director of Infectious Diseases at the Policlinico San Martino hospital in Genoa. "In particular, the neurological picture predominates, demonstrating the tropism of H3N2 for many organs including the lungs and the brain. If the morning is any indication...it will not be a good flu season'. H3N2 is the Australian variant of seasonal influenza, but it increases the risk of complications. These include pneumonia, which especially in Australia and the southern hemisphere is causing millions of infections and thousands of hospital admissions. The first case of influenza in Italy was recorded on 11 October in Novara, but when it arrives it means that the virus is already circulating in the population. As for the strains, if last year the Ah1n1 subtype derived from swine flu was dominant, according to Iss forecasts, this year a circulation of type A viruses is expected, with a predominance of A- H3N2, i.e. the so-called Australian.

Lopalco: virus always bad, the more we study it the more dangerous we see it

"The influenza virus has always been 'bad'. The novelty is that the more we study it, the more we discover its dangerousness'. This is how epidemiologist Pier Luigi Lopalco, intervenes on the alarm of these days on the particular aggressiveness that the flu is likely to have this year. 'The virus,' explains Lopalco, 'is always the same, only that every now and then some of its misdeeds become evident, such as that it can also cause neurological damage. In reality, there is no mutation of the virus this year that has made it, as it were, more dangerous for the central nervous system. Like other respiratory viruses it can give this kind of serious complication, the more we study it the more we learn to fear it'. At the research level, in fact, 'there is some attention. And as we study the effects of these viruses in more detail, we find that, to some extent, these characteristics have always been observed, but now they are being checked more carefully'. The vaccination campaign against influenza 'has started on time, therefore in a more timely manner than last year, this bodes well,' continues Lopalco, professor of Hygiene at the University of Salento. This year, moreover, 'the fact that there has been a ministerial awareness campaign, which is very important in these cases, is a noteworthy positive element. So we hope that this increased focus on the vaccination campaign will bring results'.

Ciccozzi: real problem will be increased cases with Jubilee

"Finally the H3N2 Australian flu has arrived, which so many were hoping for saying 'it will be terrible', but for now we have a few cases in Lombardy, Piedmont and Lazio. A case with neurological problems has been isolated in Genoa, but it is a case that does not make statistics. To say from this that the flu will make billions of infections this year, and that it will hit the brain, seems to me only to be in a hurry to put fear into people. Just as you cannot predict the peak today and say it will be early: nobody has Harry Potter's wand. Let's worry about the Jubilee, because it could increase respiratory disease contagions. So, my advice is masks on the means of transport since millions and millions of pilgrims will be arriving in Rome and Lazio, as early as 8 December'. Thus to Adnkronos Salute, epidemiologist Massimo Ciccozzi. 'We must say instead,' he emphasises, 'that a mix of viruses is circulating. In addition to H3N2, there are Sars-CoV-2 and the respiratory syncytial virus. Good communication does not terrorise, but explains who and why they must vaccinate: today those over 65, those who are immunocompromised and those with major chronic diseases must immunise themselves,' he concludes.

Simit: 'expected increase in encephalitis with Australian influenza'

"We have already seen in the other hemisphere, where winter arrives earlier than ours, that the Australian flu is a very serious disease with many cases, more than 15 million, and with many hospitalisations, so on this data we must obviously fear that there will be a particularly serious form of influenza in Italy too. We must expect a higher number of encephalitis than we have recorded in previous years'. So said Massimo Andreoni, scientific director of Simit, the Italian Society of Infectious and Tropical Diseases, on the sidelines of the meeting organised by Pfizer for the presentation of the 'Abituati a proteggerti' (Get used to protecting yourself) campaign, to raise awareness of the importance of vaccination against respiratory infections, particularly among the over 60s and people with chronic diseases. "Let us remember, however, that in Italy on average between 5,000 and 15,000 people die every year from influenza, so obviously when we are talking about a particularly severe form such as the Australian flu, we must expect a lethality that is particularly important, and therefore vaccination becomes fundamental. Vaccine protection remains a valuable ally. 'The flu vaccine is formulated each year according to what has circulated and what we expect to circulate in Italy. It is good to remember that all influenza viruses can reach the central nervous system and can therefore give even very serious and very relevant encephalitis. The more severe the flu form, the more we will observe a higher number of cases with central nervous system involvement,' he concludes.

The beginning of the flu season

They call it the 'Australian variant', calling it a 'child' of the one that hit Australia hard in the season that just ended there. And predicting that it could leave behind some 15 million new infections. Last year 14.6 million Italians were affected by flu-like syndromes, with a peak recorded in the last two weeks of 2023. The first Italian case of influenza of the 2024-2025 season was detected through molecular biology methods on 9 October in Novara, at the University Hospital. The patient admitted, a 42-year-old adult, was in fair and stable condition. 'Following molecular typing,' explained the Novara hospital's health staff, 'the case was found to be caused by an influenza virus of the H1N1pdm type.

The symptoms

How to recognise the 2024-2025 flu season? Regardless of the viral strain, the symptoms are similar. Virologist Fabrizio Pregliasco lists them: 'The main signs to look out for include fever over 38 degrees, at least one respiratory symptom such as cough and runny nose, and at least one general symptom such as reddened eyes, and muscle and joint pain'. What to do? 'The appearance of these manifestations, especially in combination, should prompt one to consult one's doctor,' the virologist emphasises. 'Certainly, for everyone, including the elderly, the use of an anti-inflammatory with responsible self-medication is recommended, i.e. without excesses. For the elderly and frail patients, a swab is suggested immediately to rule out the presence of Covid, the treatment of which would require the use of the antiviral Paxlovid. The latter is indicated for the treatment of patients aged 18 years and older, with confirmed SARS-CoV-2 infection, who do not require oxygen therapy and are at high risk of progression to severe Covid. For example, patients with oncological diseases, cardiocerebrovascular diseases, uncompensated diabetes mellitus, chronic bronchopneumopathy and severe obesity'.