Hong Kong flu: what kind of virus is it and what are its symptoms

In mid-July 1968, about half a million people in Hong Kong fell ill within two to three weeks. The virus culture was sent to the London Virus Centre, where it was confirmed that the pathogen did not resemble any previously known one. Thus began the third influenza pandemic of the 20th century — the very one now called the Hong Kong flu.

What the Hong Kong flu is and where the name comes from

The Hong Kong flu, or A2-Hong Kong, is caused by the H3N2 strain of influenza A virus, which mutated from H2N2; the name stuck because of the place of the first outbreak. That pandemic is classified as moderate in severity. By the end of August the disease had spread to Singapore, Malaysia, Taiwan and the Philippines; in September it reached India, Japan, northern Australia and the western United States, and it appeared in Europe at the same time; by the beginning of 1969 it had covered Africa and South America.

The death toll is an estimate: there are no reliable global statistics, and experts speak of one to four million deaths from 1968 to 1970, and of 33,800 in the United States. The Spanish flu of 1918–1919 claimed significantly more lives. People over 65 were most often affected; four months after the epidemic began, a vaccine against H3N2 was developed.

How the Hong Kong virus differs from seasonal flu

Today the "Hong Kong virus" in the news is an old acquaintance: varieties of H3N2 remain in circulation as a seasonal flu strain and do not lead to global catastrophic consequences. The reason is the immunity developed by most of the world's population: after that, outbreaks ceased to be pandemic in nature. Seasonal flu is a respiratory infection that millions of people contract every year; the course may be mild, but severe and fatal outcomes are possible.

The distinguishing feature of the Hong Kong variant is its rapidity: symptoms appear 1–2 days after infection, and the severe condition lasts about 4–5 days.

Symptoms of the Hong Kong flu

For this variety, a rapid onset is described: a temperature above 39 °C, dry cough, nasal congestion, headache, aching all over the body, vomiting, diarrhea. Seasonal flu also comes on suddenly, and its signs include:

• a sharp rise in temperature, chills;
• aching in the body and muscle pain;
• dry cough, sore throat, runny nose or nasal congestion;
• headache, fatigue and exhaustion, difficulty sleeping, loss of appetite;
• in children — ear pain, red eyes, enlarged glands, noticeable lethargy.

A cold develops over one or two days and mainly affects the nose and throat, whereas flu knocks a person off their feet within a few hours and is felt throughout the body.

How the virus is transmitted and who is at risk

Flu is highly contagious: the virus spreads in droplets when coughing, sneezing and talking and enters the mouth or nose of people nearby; less often people become infected by touching a surface with the virus and then their face. The pathogen survives on hands and surfaces for up to 24 hours, and a person is most contagious in the first five days after infection.

A severe course is more likely in people aged 65 and older, in pregnant women, in children under 5, in people with chronic diseases — asthma, diabetes, heart, lung, liver, kidney, brain or nervous system diseases — and in patients with weakened immunity. The Hong Kong pandemic also struck primarily the elderly.

How flu is diagnosed

The doctor asks about symptoms and medical history and assesses breathing and general condition. For confirmation, a swab is taken from inside the nose or from the back of the throat and tested for influenza virus: rapid tests give an answer in 15–20 minutes but are less accurate, while others take an hour or several hours.

Complications and when a doctor is needed

The Hong Kong flu can result in pneumonia, myocarditis, encephalitis and meningitis, and exacerbation of heart disease, asthma and diabetes mellitus; excess mortality after the pandemic was observed for about another ten years. Seasonal flu has a similar list: bronchitis, ear and sinus infections, pneumonia, inflammation of the heart, brain or muscle tissue, exacerbations of asthma and other chronic diseases.

You should consult a doctor without delay if a person feels severely unwell, has developed shortness of breath, or symptoms do not improve after 7 days; the same applies to pregnant women, women who have recently given birth, people aged 65 and older, patients with chronic diseases and weakened immunity, as well as alarming symptoms in a child.

A high temperature in itself with flu is not a reason to call an ambulance; 103 or 112 — if sudden chest pain occurs, severe shortness of breath develops in which the person gasps and cannot utter a word, or a cough with blood begins.

This material is for reference: it describes what is known about the virus and its symptoms, but does not replace consultation with a doctor who sees a specific person.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer