Influenza on the rise in Singapore
The burden of influenza in Singapore has been increasing since 2010, according to a recent study. Vaccination programmes, especially for the young and the elderly, should be a continued priority.
Drawing from the national surveillance programme for influenza of the Ministry of Health, researchers determined influenza activity from 2010–2017 by using all records of laboratory-confirmed influenza positivity as a proxy measure. Generalized additive negative binomial models were used to estimate the number of weekly admissions for pneumonia and influenza (P&I) associated with influenza activity.
Over the 8-year study period, Singapore registered an average weekly temperature of 27.9°C and relative humidity of 80.8 percent. During this time span, 319±88 P&I hospitalizations were reported. [Influenza Other Respir Viruses 2019;doi:10.1111/irv.12676]
Stratifying according to age revealed an upward trend. In the 0–4-year age-group, there was a mean of 33±12 P&I hospitalizations between 2010 and 2017. This rose to 55±16, 47±14 and 183±54 at age 5–49, 50–64 and ≥65 years, respectively. P&I hospitalizations also changed linearly over time, growing steadily from 239.2 per 100,000 person-years in 2010 to 416.2 per 100,000 person-years in 2017.
In terms of influenza activity, a total of 22,090 specimens were tested for virological surveillance. Positivity likewise increased over time, rising from a low of 40.9 percent in 2011 to a peak of 53.6 percent in 2016. The influenza A subtype dominated the positive samples every year.
Overall, the researchers estimated that 16.3 percent of all P&I hospitalizations from 2010 to 2017 could be attributable to influenza. This led to an excess hospitalization rate of 50.1 per 100,000 person-years. Excess proportion was greatest in individuals aged 0–4 years, where influenza accounted for 24.1 percent of all P&I hospitalizations, resulting in an excess hospitalization rate of 186.8 per 100,000 person-years.
Notably, influenza was responsible for only 16.5 percent of all P&I hospitalizations from 2010–2017 in individuals ≥65 years of age, the resulting excess hospitalization rate was the highest among all the age groups at 338.0 per 100,000 person-years.
“These results suggested that while both the young and the elderly were more prone to influenza‐attributed hospitalizations older people were also particularly at risk of developing severe symptoms, and requiring hospitalizations, from other pathogens,” the researchers explained.
They also noted a general upward trend in the proportion of hospitalizations due to influenza. In 2011, for instance, 14.5 percent of all P&I hospitalizations were attributable to influenza. By 2016 and 2017, these rates were at 18.0 percent, each. A similar pattern was observed across all the age groups.
“Vaccination has been found to be one of the most effective ways to reduce influenza burden and also a cost‐effective intervention strategy for targeted age groups,” the researchers said, noting that there should be particular focus on the very young and very old, given their risk profiles, and during the middle of the year, where influenza burden is highest.
“Further studies should be conducted to determine the optimal vaccination schedule in countries with year-round influenza activity, especially when there is growing evidence of waning vaccine effectiveness,” they added.