The Hong Kong Medical Association Symposium on Influenza 2003 By Dr. Lo Wing-lok

The Objectives of a National Programme for the Prevention of Influenza “are to reduce the incidence of severe illness and premature death in groups at increased risk of severe disease, and as a consequence, to reduce the need for specialized health care services and pharmaceutical supplies, in particular antibiotics.” World Health Organization

Limitations of a National Programme for the Prevention of Influenza NOT intended to cover ALL: finite resources, finite vaccine production Will cover only the three influenza viruses, but NOT other viral (e.g. parainfluenza virus, adenovirus, rhinovirus, RSV) and bacterial causes of respiratory infection (e.g. pneumococcus) Will NOT protect recipients against SARS

Limitations of the Influenza Vaccine The circulating viruses may or may not be the same as the vaccine viruses Even if the circulating viruses are the same as the vaccine viruses the protection is not 100%: 70-90% efficacy in preventing laboratory proven influenza in healthy adult volunteers; up to 50% reduction in rates of all severe respiratory illnesses and death in persons with pre-disposing medical conditions

Limitations of the Influenza Vaccine The protection wanes with time, even if the viruses of the vaccine may remain the same for successive years, a yearly injection is recommended The protection wanes faster or slower depending on the conditions of the vaccine recipients For an average person the best protection is within the half year after the injection

Limitations of the Influenza Vaccine The protection is not immediate after the injection; it may take up to 2 weeks for protection to develop. Therefore, vaccination is best timed at not less than 2 weeks before the onset of the peak influenza season, but not too long before the onset of the peak season so as to give the recipients the best protection

Seasonal Pattern of Influenza in Hong Kong: 1998

Seasonal Pattern of Influenza in Hong Kong: 1999

Seasonal Pattern of Influenza in Hong Kong: 2000

Seasonal Pattern of Influenza in Hong Kong: 2001

Seasonal Pattern of Influenza in Hong Kong: 2002

Seasonal Pattern of Influenza in Hong Kong: 2003

The Best Months for Taking the Influenza Vaccine in Hong Kong The best months for taking the influenza vaccine in Hong Kong is November and December each year Taking the vaccine in January is not too late Taking the vaccine in October is not too early

The Pressure on the Government to Start Vaccination Programme Early is Unwarranted Many of the ‘outbreaks’ in institutions earlier this year were not caused by the influenza viruses (5 outbreaks of respiratory illnesses in homes for the elderly and 1 outbreak in a child care centre in September 2003 were due to RSV) Because of the later onset and the longer duration of the Hong Kong influenza season, the protection of persons receiving the vaccine too early will be sub-optimal Consistency required in any public health programme

Target Groups for Influenza Vaccination (In order of priority) Residents of institutions for the elderly or the disabled (2 risk factors or more) Elderly (65 or above) non-institutionalized individuals with 1 or more of the following chronic conditions – chronic cardiovascular, pulmonary, metabolic or renal disease, or immunocompromised (2 risk factors) Non-institutionalized persons aged >6 months to 64 years with 1 or more of the chronic conditions of 2. (1 risk factor)

Target Groups for Influenza Vaccination (In order of priority) Persons aged 65 or above (1 risk factor) Health care workers (risk to high risk persons) Household contacts of high risk persons (risk to high risk persons)

Safety of the Inactivated Influenza Vaccine “Influenza vaccine conforming to international standards of purity and potency have been used for many years and have an excellent safety record” (WHO) Local reactions at the site of injection Short lasting fever The 1976 ‘swine flu’ vaccine was associated with Guillain Barre Syndrome at an incidence of 10 in a million vaccine recipients; no such association was observed for vaccines of subsequent years

Egg (egg protein) allergy Allergy to other components of the vaccine Those Who Should Not Receive the Influenza Vaccine (subject to the individual advice of a physician) Egg (egg protein) allergy Allergy to other components of the vaccine Previous reaction to the influenza vaccine History of Guillain Barre Syndrome