For the week ending 3rd January 2015, influenza activity in the US remained above epidemic levels, defined by the pneumonia and influenza mortality surveillance that was above the epidemic threshold of 6.9% for that week. The laboratory confirmed influenza hospitalisation rates have also gone up in all age groups, alarmingly so for those who are more than 65 years of age – as shown in chart below which was downloaded from the CDC Fluview site.

Laboratory-confirmed influenza hospitalisations in the US by age group (source: CDC Fluview)

While it remains unclear whether this flu season will be better or worse than previous years – that will most likely only be certain by April – there are several indicators that are worrying. As mentioned previously, this season’s dominant influenza strain is not largely not covered by the current influenza vaccine. The dominant influenza strain is also a H3 influenza A virus, which in the past had always resulted in worse flu seasons. Compared to previous years (which can be done from the very useful Fluview website), rates of hospitalisations due to influenza are already significantly higher than previous years.

Comparison of influenza hospitalisation rates among those age 50 and above for the current and past 5 influenza seasons (source: CDC Fluview)

The US CDC Director Dr. Thomas Frieden has publicly urged doctors in the US to prescribe antivirals for patients suspected of having influenza, notwithstanding the controversy over the effectiveness of the neuraminidase inhibitors such as tamiflu. I believe this recommendation has arisen partly because the CDC experts believe that these drugs are somewhat effective (i.e. better than nothing), and there is little else that can be done to mitigate the impact of influenza this time round.

What is the situation in Singapore? This can be found in the Weekly Infectious Diseases Bulletin published by the Ministry of Health – the Week 53 issue can be downloaded here. Although the majority of influenza viruses typed in December 2014 was also Influenza A H3N2 (85.7% – it’s not clear from the report how this percentage was derived, but the number of samples tested was small) – mirroring the situation in the US – the number of polyclinic attendances for acute respiratory illnesses did not increase (screenshot below). Hopefully this situation will not change over the next few weeks (Singapore’s influenza “season” is from December to February, according to the Health Promotion Board).