Dr Leong Ho Nam, an infectious diseases expert at Mount Elizabeth Novena Hospital said that this is caused by a mutated H3N2 strain of the influenza virus that few in Singapore have immunity against. Singapore's flu season is parallel to that of countries in the Southern hemisphere, such as Australia, thus some Singaporeans may have picked up the virus while travelling in Australia during the school holidays in June, he added.
The strain has affected the whole world, spreading through travellers. As the strain is recently mutated, a lot of people are naive to it.
The Health Ministry also confirmed there is "evidence of increased influenza activity in recent weeks from the rise in the proportion of cases where influenza viruses have been isolated". The rise has been consistent with what is typically seen during the flu season, which lasts between November and February and May and August each year.
Low H3N2 vaccination rate causes poor herd immunity
In 2014, a genetic mutation to the H3N2 virus strain made it the most prevalent strain for 2015 in Singapore. This year, H3N2 has emerged once again as the dominant strain among those who tested positive for the flu in June. MOH said that of specimens that tested positive for influenza that month, more than 80% came back positive for the influenza A (H3N2) strain.
Dr Leong said despite the local population being exposed to the virus, it takes "a few years" for it to make its rounds, and for people to build up their herd immunity against it.
A vaccine for the strain has been available since October 2015, according to Dr Leong. However, less than 5 to 10% of the population are vaccinated against it.
"For good protection, you need at the barest minimum 60 to 80% of the population coverage and we are clearly not reaching that. So in terms of herd immunity protection, it is very poor. One can pick it up, and in turn, spread it to colleagues and the risk of transmission of the influenza virus is very fast and very easy," he said.
Acute upper respiratory infection cases reach a six-month high
Acute upper respiratory infection is usually characterised by symptoms such as a cold, cough and sore throat. According to a weekly infectious diseases bulletin published by the Ministry of Health (MOH), the number of people visiting polyclinics for acute upper respiratory infections hit a 6-month high of 3,427 cases for the week ending 23 July.
However, MOH said that influenza only accounts for less than 5% of the total number of ARI cases. "Acute respiratory infections (ARI) are very common and are caused by a large number of different viruses, including influenza," the statement said.
Dr Tan Tze Lee, a GP at Edinburgh Clinic, said symptoms in patients seem to be more "uncomfortable". "We're seeing more cases of high fevers in patients - of 39 and 40 degrees Celsius. The typical runny nose, cough and sore throat are also more uncomfortable. And they're taking longer to clear," he said.
Authorities urge vaccinations to boost herd immunity
The number of flu infections is expected to remain high throughout the rest of the year, mainly because of the lack of immunity against the virus in individuals and the population. The flu season in the Northern hemisphere is also expected to start and may infect Singaporean travellers intending to travel to those parts of the world.
MOH said most people with the flu recover with rest and "symptomatic treatment" - treatment of the symptoms - but urged young children, pregnant women, the elderly and those with chronic diseases to get vaccinated as soon as possible. MIMS
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