Flu vaccine no shot in the dark

PUBLISHED : Tuesday, 01 November, 2011, 12:00am
UPDATED : Tuesday, 01 November, 2011, 12:00am


The impending winter brings with it the influenza season, and this year, the Health Department is stepping up its vaccination drive.

Compared with last season, those aged between 50 and 64, as well as the obese, have now been included as a target group for the influenza vaccination. This was based on recommendations by the Scientific Committee on Vaccine Preventable Diseases under the Health Department's Centre for Health Protection, because the local influenza epidemiology showed a higher risk of flu-related deaths and admissions to intensive care units in this age group last season.

Furthermore, local and overseas evidence suggests that obesity - that is, having a body mass index of 30 or above - is an independent risk factor for severe influenza A (H1N1) 2009 (human swine influenza virus) infection, and is linked with ICU admission or death.

'It is likely that [this] strain will continue to circulate in the 2011-12 season,' says a Health Department representative.

Among others at risk of serious infection are those with chronic illnesses, elderly (65 years and above) and disabled people in residential care, children (six months to under six years), health workers, pregnant women, and people working with poultry and pigs.

But apart from these priority target groups, the seasonal influenza vaccination is recommended and suitable for everyone, except those with known contra-indications.

In Hong Kong, the two subtypes of influenza A virus, H1N1 and H3N2, are most commonly seen, with peaks from January to March and from July to August. The virus spreads mainly by respiratory droplets, and is characterised by fever, sore throat, cough, headache, muscle aches, runny nose and general tiredness.

Although it is usually self-limiting, with recovery in two to seven days, it can be serious for the weak and frail. It may be complicated by bronchitis or chest infection, and even death can occur. Earlier this year, a case-based surveillance system was set up in collaboration with the Hospital Authority and private hospitals to monitor flu-related ICU admissions or deaths from January 24 to March 31 during influenza peak season. A total of 123 severe cases, including 34 deaths, were recorded.

Vaccination is safe and effective in preventing flu infection in 70 to 90 per cent of healthy adults, says the World Health Organisation. Among the elderly, immunisation prevents severe complications and death in 60 per cent and 80 per cent of cases, respectively, it says.

There are two types of vaccines in Hong Kong: the 'flu shot' - an inactivated influenza vaccine containing dead viruses - and a nasal-spray vaccine, a live attenuated influenza vaccine that contains weakened viruses. The difference between them is that most inactivated influenza vaccines are licensed for use in those aged six months or older - whether healthy, with chronic medical problems, or pregnant. But live attenuated influenza vaccines are licensed for use only among healthy, non-pregnant people aged two to 49.

It takes about two weeks after vaccination for antibodies to develop in the body and provide protection.

Of course, the usual prevention measures, such as good personal hygiene, balanced diet, regular exercise, adequate rest, and no smoking, are also important.

As the circulating seasonal influenza strains may change from time to time, it is vital to get a vaccination every year. The vaccine composition is updated each year to enhance protection.

This year's influenza vaccine composition contains a human swine flu virus (A/California/7/2009 (H1N1)-like virus); an A/Perth/16/2009 (H3N2)-like virus; and a B/Brisbane/60/2008-like virus.

This is as recommended by the WHO and the Scientific Committee.

To encourage the target groups to get vaccinated, the government has a number of free and subsidised vaccination programmes and schemes. From today, eligible people and residents of elderly or disabled homes can get free immunisations.

In addition, since September 26, children are entitled to a HK$80 subsidy per dose of seasonal influenza vaccine (for one or two doses) received from enrolled private doctors, and the elderly can receive a HK$130 subsidy per dose of flu vaccine and HK$190 per dose of pneumococcal vaccine.

For more details, visit the Centre for Health Protection website www.chp.gov.hk