Tackling influenza with vaccination
View(s):By Dr. Jude Jayamaha
Influenza is a viral infection often presenting as a “flu-like” illness and is considered a major public health problem. It spreads rapidly in the community especially among children, elderly people and high-risk groups such as pregnant women and healthcare workers. Children manifest the highest rates of illness. However, severe morbidity and mortality are more common among elderly people and high-risk groups.
In the west, seasonal influenza epidemics are seen mainly during the winter months whereas in tropical climates like ours, influenza occurs throughout the year, resulting in outbreaks that are more unpredictable. Therefore, morbidity and mortality from influenza are likely to be underestimated in the tropics. In Sri Lanka, for the last few years, it has been generally observed during April to June and again from November to January. There could be shift of a month or two either way in this seasonality. Sri Lanka experienced an outbreak of influenza from January to May this year due to the Influenza AH1N1 strain.
Influenza viruses are classified into types A, B and C on the basis of their protein structure. Only influenza A and B are clinically important in human disease.The structure of the virus mutates frequently. Minor mutations of its genetic structure lead to changes in the virus protein composition (“antigenic drift”), resulting in frequent influenza outbreaks. Major changes to its protein structure (“antigenic shift”) occur less frequently by the mixing of genetic material from different types of Influenza A viruses and cause major influenza epidemics like the Influenza A (H1N1) epidemic in 2009.
In Sri Lanka, the national surveillance on influenza is carried out by the Health Ministry through its technical institutions including the Epidemiology Unit dealing with disease surveillance and the Medical Research Institute providing laboratory testing.
Vaccination is currently the leading effective means of reducing the burden of morbidity and mortality of influenza in the community. Constant structural changes in influenza viruses mean that the vaccines’ virus composition must be adjusted annually to include the most recent circulating influenza viruses.There are two types of vaccines available against influenza, namely live attenuated and inactivated influenza vaccines.
The influenza vaccine contains three influenza viruses: Two Influenza A virus strains — A (H1N1) virus and A(H3N2) and one Influenza B virus strain in the trivalent vaccine. Four influenza viruses: Two Influenza A virus strains, A (H1N1) virus and A (H3N2) and two Influenza B virus strains in a quadrivalent vaccine. The virus strains in the vaccine change each year based on global surveillance and scientists’ estimations which types and strains of virus will circulate during the next season.
There are two types of vaccine formulations for the northern and the southern hemispheres. For countries in equatorial regions, epidemiological considerations influence the choice of the vaccine. Currently the southern hemisphere vaccine is registered in Sri Lanka.
The influenza vaccine is recommended for the following individuals to reduce the incidence of severe illness and death:
All persons 65 years and older (people above nationally defined age limit for old age)
a. Residents of institutions for the elderly or the disabled
b. Elderly, non-institutionalized individuals with chronic conditions, chronic cardiovascular, pulmonary, metabolic or renal disease, or who are immunocompromised.
Pregnant women – the influenza vaccine containing the killed virus is safe and is recommended for all pregnant women. The influenza vaccination in pregnancy will protect the mother and the newborn against influenza.
All individuals >6 months of age with any of the chronic illnesses listed above.
People who are engaged in essential services.
Household members who are in close contact with high-risk persons.
Travellers and healthcare workers.
Those who wish to reduce their chances of getting “seasonal flu”.
Inactivated influenza vaccines will not interfere with other concomitantly administered vaccines. Immunity lasts about one year and the vaccine should be administered annually.
The contraindications for the use of vaccines are:
Hypersensitivity to any component of the vaccine
A previous allergic reaction to any influenza vaccine
(Source WHO & CDC, SLMA Vaccine Guideline Book 2017)
(The writer is a Consultant Virologist at the National Influenza Centre, Medical Research Institute, Colombo)
| How the virus spreads The virus is primarily spread from person-to-person via inhalation of droplets formed during coughing and sneezing or by direct contact with articles contaminated with respiratory secretions. Inhaled virus particles initiate infection in the respiratory tract, although transmission can also occur through the mucous membranes of the eyes, nose and mouth. The incubation period can range from 1 to 4 days. The infection usually lasts for about a week. It is characterized by the sudden onset of high fever, muscle pains, headache, severe malaise, dry cough, sore throat and nasal discharge. Most people recover within 1 to 2 weeks without requiring any specific medical treatment. In very young children, pregnant women, the elderly and people suffering from medical conditions such as lung diseases, diabetes, cancer, kidney or heart problems, influenza poses a serious risk and may need specific drug treatment. In these people, the infection may lead to severe complications of underlying diseases, pneumonia and even death. | |