What is Influenza A and how dangerous is it?

Jakarta (ANTARA) - Influenza A is currently drawing attention following reports of increased influenza virus findings in several regions of Indonesia. The issue has also caught the attention of the Indonesian Pediatric Society (IDAI), which is urging the mapping of regions and influenza spread patterns, especially since some cases have been found in the paediatric group.

Latest data from the Ministry of Health up to 19 September 2026 shows that the proportion of positive influenza in week 36 surveillance reached 46 per cent, up from 35 per cent the previous week. Out of 185 specimens examined, there were 86 positive influenza cases, consisting of 76 influenza A(H1N1)pdm09, eight A(H3N2), and two influenza B Victoria. Approximately 42 per cent of detected influenza cases originated from the 0-4 age group.

Nevertheless, the Ministry of Health stated that the overall level of influenza activity remains in the low category and the situation is still under control. Therefore, while news regarding influenza A warrants attention, it does not mean that every finding of influenza A indicates an emergency or an outbreak.

So, what exactly is influenza A and how dangerous is the disease?

What is influenza A?

Influenza A is a type of influenza virus that can cause infections in the human respiratory tract. The World Health Organisation (WHO) explains that seasonal influenza in humans is most frequently caused by influenza type A and B viruses. Influenza A is further divided into several subtypes based on two proteins on the virus surface: haemagglutinin (H) and neuraminidase (N).

Some circulating subtypes of influenza A in humans include A(H1N1)pdm09 and A(H3N2). A(H1N1)pdm09 was the virus responsible for the 2009 influenza pandemic. Since the end of that pandemic, this virus has become one of the seasonal influenza viruses that continue to circulate. Therefore, when the name H1N1 reappears in current influenza reports, it does not mean the 2009 pandemic is recurring; H1N1pdm09 is now part of the seasonal influenza viruses circulating in humans.

How is influenza A transmitted?

Influenza A can spread relatively easily from one person to another. Transmission primarily occurs through respiratory particles when an infected person coughs, sneezes, or speaks. The risk of transmission can also increase when a person is in crowded places and has close contact with someone who is ill. This is why influenza can spread quite quickly in environments such as schools, workplaces, homes, healthcare facilities, or other enclosed spaces.

In Indonesia, influenza can circulate year-round. The Ministry of Health notes that influenza activity can be influenced by weather factors and has the potential to increase during the rainy season.

Symptoms of influenza A are fundamentally not very different from other types of influenza. The WHO states that influenza symptoms usually appear suddenly. Common complaints include fever, cough, sore throat, runny nose, headache, muscle and joint pain, and significant fatigue. A cough may also last longer than other symptoms, even up to two weeks or more. For some people, symptoms may feel like a common cold and improve on their own within about a week. However, there are also conditions where influenza develops into a more serious illness.

Is influenza A dangerous?

The answer is, it can be. Most people affected by influenza can recover without requiring special treatment. However, influenza can also cause complications, especially in high-risk groups. The WHO identifies children under five, the elderly, pregnant women, and people with certain chronic diseases as groups at higher risk of severe influenza.

Chronic diseases that can increase the risk of complications include heart, lung, kidney, and liver diseases, metabolic disorders, and several conditions affecting the immune system. Influenza complications can manifest as pneumonia or lung infections. In severe cases, infection can lead to sepsis and organ failure. Influenza can also exacerbate pre-existing conditions, such as asthma or lung and heart diseases. Therefore, the assumption that influenza is merely a “common flu” is not always accurate; the risk of illness depends heavily on the condition of the infected individual.

The name influenza A(H3N2) subclade K was also widely discussed in Indonesia throughout 2026. The Ministry of Health previously issued a special circular regarding the management of influenza A(H3N2) subclade K. The document noted that subclade K was first detected in Indonesia in September 2025, and by 10 January 2026, 74 cases had been found across 13 provinces. The Ministry of Health also noted that the majority of cases showed mild to moderate symptoms.

In the latest surveillance report up to 19 September 2026, the Ministry of Health still recorded the presence of H3N2 subclade K in 13 provinces. However, surveillance data also showed that there were no positive influenza cases requiring ICU admission in the sentinel hospitals examined during week 36. This means that the term ‘subclade K’ does not automatically imply that an individual will suffer from severe illness; severity remains influenced by individual condition, age, co-morbidities, and various other factors.

When to see a doctor?

Flu can usually improve with rest and adequate fluid intake. However, the public should be more vigilant if symptoms worsen or do not improve. Difficulty breathing, shortness of breath, chest pain or pressure, confusion, severe dizziness, extreme weakness, dehydration, or a condition that initially improved but then worsened are signs that require medical attention. The Ministry of Health also advises the public to immediately access healthcare facilities if symptoms worsen or do not improve after more than a certain period.