1. Mutation in a dominant flu strain
Unlike the winter H3N2 outbreak in 2014/15, no antigenic drift is observed during the summer influenza season this year. However, a study published in 2017 in Denmark has revealed several genetically drifted viruses, including N121K. Results showed that some of the drifted viruses appeared to be more prominent in vaccinated or non-vaccinated individuals, respectively.
From July 2016 to March 2017, N121K was found to be responsible for 20% of the H3N2 mutation, in Hong Kong. The percentage further went up to more than 35% in May 2017—and this could be one of the reasons, which contributed to the surge of flu cases.
2. The dense population of susceptible individuals
People would build up natural antibodies if they were infected with H3N2 during the 2014/15 winter influenza season. Nevertheless, such protection only lasted for a very short term—and the level of natural antibodies has already gone down to an extremely low level until this point of time. On the other hand—since the effectiveness of flu vaccines drop after around six months—some of the populations became susceptible individuals even when they had taken flu shots last year.
The dense population of susceptible individuals surrounding each infective individual has, to a certain extent, contributed to the spread of infection.
1. Giving out Tamiflu to elderly people
The hospital admission rate for older adults of 65 years or older with known chronic disease has remained high. This population is also at a greater risk of severe influenza complications and mortality.
Both experts urged the Hong Kong government to consider offering 14-day dosing regimen of Tamiflu to the vulnerable elderly aged 65 or above in nursing homes and public outpatient clinics as one of the flu prevention strategies. While the potential side effect of a once-daily dosing of Tamiflu is mild, except for renal disease patients, study proved that the efficacy in prevention could be satisfactory.
As of now, the Hong Kong government owns more than 16 million of Tamiflu vaccines. Meanwhile, there are about 1 million elderly people aged 65 or above in 2016, of which about 75, 000 elderly persons live in nursing homes.
Both experts have raised their concerns that the government must act immediately and aggressively to control the current flu outbreak. They emphasised the flu prevention measurement must be carried out within the next week to grasp the window of opportunity.
In response to the recommendation, a spokesperson from the Department of Health (DH) commented that offering Tamiflu as a preventive measure to those who are not exposed to health risks ‘would not be a justified move’.
“But the department will consider the recommendations [from the professors] as part of a review of flu prevention strategies,” he expressed.
2. Keeping children at home
According to statistics from the Centre for Health Protection (CHP), the influenza associated hospital admission rates among 0-4 years old children almost doubled that of the population who are aged 65 years old or above. Nonetheless, the 14-day dosing regimen of Tamiflu is not practical to be used as the preventive measurement on children. This is because children tend to suffer from the side effects of the medications.
As a result, the experts advise parents to keep their children at home or avoid any visits to crowded public places in these two weeks. People are also advised to keep up with good personal hygiene practice—such as washing hands with liquid soap and water (or alcohol-based hand sanitisers) before touching their mouths, nose, or eyes, or after public installation.
In addition, both highlighted the key to tackle the flu outbreak is the implementation of preventive measurements, instead of resolving the bed-shortage issue in the overloaded paediatric wards. MIMS
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