H3N2 Influenza surge in Thailand
Thailand is currently experiencing a surge in influenza with more than 160,000 cases and 100 deaths reported between mid-October and mid-November 2025. The H3N2 strain of influenza A accounts for more than 70% of cases. It is also the dominant strain (> 95%) of influenza in a large outbreak in China.
This strain is included in the annual flu vaccine.
Influenza vaccine and travel.
People often confuse a common cold with flu. “Colds” are due to several viruses which have a similar clinical picture. Colds are common, hence the name “common cold”. They are generally annoying rather than disabling. Fortunately, influenza isn’t common, but it can be very unpleasant. A bout of influenza can last for several days. The symptoms can include fever, chills, dry cough, headaches, and severe fatigue. It is also highly contagious.
If you are a member of travelling group, you might be the index case for the group and the start of a holiday from hell. It might also be a particularly important holiday, a honeymoon or a 30th wedding anniversary. It might also be an important business trip. It is always important to consider the flu vaccine if there is something you would prefer not to miss!
The flu vaccine is the first vaccine you should consider in the context of travel. Influenza is the commonest health issue which can be prevented by vaccination.
Flu vaccination should never be considered in an age-based context when travelling. It is true that a person aged 20-40 years is less likely to experience serious illness, hospitalisation, or death but they also have something to miss!
Flu vaccination rates in Asia vs Australia
It is also important to know that fewer people are vaccinated for influenza in Asia. This means it can circulate more widely. The picture is different in Australia. Prior to the pandemic, up to 10 million were vaccinated annually with the highest rates being in those over 65 years (60%). A higher number of people being vaccinated means less transmission. Unfortunately, fewer people have been vaccinated in the last couple of years.
How effective are flu vaccines?
The effectiveness varies from year to year. It really depends on how close in structure is the vaccine to the circulating strains. Sometimes it is very close and at other times not so good. It is generally accepted that the effectiveness ranges from 40%-60%. The vaccines work better against the B strains of the virus and the H1N1 of the A strain but not so well for the H3N2 strain. It then depends on the predominant strain for the season to determine whether the vaccine was effective for the season.
A study of the 2019-2020 season (pre-pandemic) in the USA showed that vaccination prevented 7 million influenza-related illness, 3 million clinic visits, 100,000 hospitalisations and 7,000 deaths.
