The HCM City Centre for Disease Control (HCDC) reported 34,664 acute respiratory infection cases in week 40 of 2026, marking a sharp increase in respiratory illnesses across the city.
Hospital surveillance identified 151 samples testing positive for influenza viruses, with the A/H1N1 2009 strain accounting for nearly 77 per cent.
Acute respiratory infection cases in HCM City rose by more than 64 per cent in week 40 compared with the previous four-week average.
Hospitals have reported a growing number of patients seeking treatment for respiratory illnesses in recent weeks.
At Tam Anh General Hospital's District 8 facility, around six to seven in every 10 patients presenting with respiratory symptoms were diagnosed with influenza A.
Severe cases were reported mainly among older patients, particularly those with underlying medical conditions.
Dr Ngo Tran Quang Minh, medical director and head of general internal medicine at Tam Anh General Hospital, said older people were more vulnerable to serious complications because of age-related declines in immunity.
Patients with heart disease, asthma, diabetes, COPD or kidney disease face a higher risk of severe pneumonia, respiratory failure and other complications, even after mild initial symptoms.
Influenza can also worsen underlying conditions, increasing the risk of heart attacks, strokes, uncontrolled blood sugar and organ failure.
Dr Le Thi Ngoc, a paediatrician at Tam Anh General Hospital in HCM City, said influenza A commonly circulates as H1N1 and H3N2 strains, which can change over time and cause repeated infections.
Cases typically increase in September and October as children return to school, where close contact and shared objects can facilitate transmission.
Symptoms in children include fever, coughing, a runny nose, sore throat, fatigue and sometimes vomiting. Most recover within five to 10 days, although some develop bronchitis or pneumonia.
In rare but serious cases, influenza can cause neurological complications, including encephalitis and acute necrotising encephalopathy. Seizures, confusion or altered consciousness require urgent medical assessment.
Health authorities urge vaccination and preventive measures
HCDC said it was strengthening respiratory disease surveillance across 29 healthcare facilities, including hospitals and regional medical centres, while closely monitoring community infection clusters.
Continuous testing and identification of circulating viruses will help authorities assess transmission risks and introduce appropriate interventions.
Health authorities advise people with fever or respiratory symptoms to wear masks in public places.
Doctors warned against self-medicating with antibiotics or antiviral drugs without medical advice, as inappropriate treatment could delay diagnosis or cause adverse effects.
Antiviral treatment is generally most effective when started early, particularly for patients at higher risk of complications.
Older people experiencing breathing difficulties, chest pain, confusion, bluish skin or worsening underlying conditions should seek emergency medical care.
Health experts also emphasised the importance of annual influenza vaccination, particularly for older adults and people with chronic illnesses.
Accoridng to Dr Bach Thi Chinh, medical director of the VNVC vaccination system, seasonal influenza vaccines available in Vietnam protect against commonly circulating strains, including A/H1N1, A/H3N2 and influenza B, depending on vaccine formulation.
She advised vulnerable groups to get vaccinated early, noting that protective immunity generally develops about two weeks after vaccination.
Annual vaccination remains important because influenza viruses evolve and immunity declines over time.
Health experts recommend annual influenza vaccination, particularly for older adults and people with underlying conditions.
HCDC also urged residents to wash their hands regularly with soap, cover their mouths and noses when coughing or sneezing, and wear masks when experiencing respiratory symptoms.
People with fever, coughing, sore throats or runny noses should limit close contact with others and seek medical advice when necessary.