| Prevention of Influenza by Vaccination |
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Module 5: VICNISS online self guided surveillance education
To download this module and/or the associated multiple choice exercises as PDF files, click on Education Resources.)
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Overview
This module gives an overview of influenza (flu) and how it can be prevented by vaccination.
Objectives
After you have completed this module you should be able to:
- Understand what influenza is;
- Explain the symptoms of influenza, and how it is spread; and
- Understand the recommendations for vaccination to prevent influenza.
Introduction
Influenza is an acute viral infection that occurs worldwide, often in winter, and
is known for its capacity to cause epidemics and pandemics with remarkable rapidity.
Influenza can be caused by one of 3 influenza viruses: A, B or C. Type A has most
frequently been associated with epidemics, and causes more severe infections. Influenza
A subtypes are classified according to the hemagglutinin (H) and neuraminidase (N)
glycoproteins on their surface. Different strains of influenza arise through mutation
of these glycoproteins, and are named according to the geographic site where it
was isolated, the culture number and the year. For example; A/Beijing/262/95(H1N1).
Influenza A viruses are also capable of altering their antigens (antigenic shift),
and interspecies reassortment between humans, swine and birds.
Mode of Transmission of Influenza
The main way that influenza viruses are spread is from person to person via droplet
spread. Droplets are propelled from a cough or sneeze of an infected person. Though
less frequent, the viruses also can be spread by direct contact with respiratory
secretions, mucous membranes or a contaminated environmental surface, since the
influenza virus is capable of surviving for long periods in the environment.
People with upper respiratory tract infections should cover their mouth and nose
with a tissue when coughing or sneezing to prevent spread of infection to those
around them. Influenza is however transmitted primarily via the airborne route in
enclosed areas, such as school buses or airplanes.
Scientific studies show that adults can shed virus from 1 day before developing
symptoms to up to 7 days after getting sick. Young children can shed virus for longer
than 7 days. In general, however, more virus is shed earlier in the illness than later.
Incubation Period of Influenza
The usual incubation period for influenza is 1-3 days.
Symptoms and Complications of Influenza
Patients predominantly experience symptoms affecting the respiratory tract, and
causes fever, headache, myalgias, anorexia, sore throat, coryza, and cough. Most
of these symptoms resolve over 2-7 days, however, the cough can have a protracted course.
Gastrointestinal tract symptoms such as nausea, vomiting, and diarrhoea are uncommon,
but may occur especially in children.
Patients shed virus and are infectious from 1 day before developing symptoms to
up to 7 days after getting sick, although this can be longer in young children.
The major serious complications of influenza are viral and bacterial pneumonias.
These are more common among the very young, the elderly, those with chronic medical
conditions (such as heart or lung disease, renal failure and diabetes) and those
who are immunosuppressed. Staphylococcal pneumonia is associated with a preceding
infection with influenza.
Influenza can also cause a worsening of chronic medical conditions, such as congestive
heart failure, asthma, or diabetes. Children may develop croup, sinusitis or ear infections.
Treatment of Influenza
Influenza cannot be cured by antibiotic therapy, and the mainstay of treatment is
supportive. Salicylates, such as aspirin should be avoided in children because they
may cause Reye's syndrome. However, several antiviral agents are available, and
if started early in the illness can prevent or modify the infection.
These agents include:
- Amantadine and Rimantadine - they are effective against Type A strains, and if started
within 48 hours of anset of influenza illness and given for 3-5 days reduce symptoms.
- Oseltamivir (tamiflu) and Zanamivir are effective against influenza A & B if
administered within 48 hours of onset of symptoms.
If bacterial pneumonia occurs it should be treated with antibiotics.
Influenza in Hospitals
Influenza can pose a major problem in hospitals in that clinical attack rates during
an epidemic can be more than 50% in such a closed population. For this reason, infection
control programs should concentrate on prevention of infection among staff, and
then prevention of transmission of infection from either staff or patients to susceptible
persons.
Staff members with febrile respiratory tract infections, consistent with influenza
or influenza-like illnesses should not be working in the c linical area, and pose
a risk to patients and other staff.
Patients who are suffering from suspected or proven influenza or influenza-like
illness should be placed in droplet precautions, which consist of wearing a mask
within 1 metre of the patient wearing gowns if clothing is likely to be soiled by
body fluids, and practicing hand hygiene before a nd after patient contact. They
should either be placed in a single room or may be cohorted with other patients
with influenza.
Patients and healthcare personnel who have not been vaccinated should be offered
influenza vaccine.
Influenza antiviral medications should be considered for treatment of ill patients
and healthcare personnel and for prophylaxis of exposed patients, unvaccinated personnel,
and those vaccinated <2 weeks before exposure.
Surveillance for Influenza
- Inpatient surveillance for influenza is important particularly during the influenza
season, and requires the following:
- Document incidence of reported influenza and influenza-like illness.
- Develop case definitions for healthcare facility-acquired and community-acquired
influenza.
- Consider patients who develop influenza-like illness >72 hours after facility
admission as potential cases of health care facility-acquired influenza-like illness.
- Initiate influenza testing and droplet precautions when healthcare facility-acquired
influenza is detected during surveillance, particularly when:
- one or more patients are identified with healthcare facility-acquired laboratory
confirmed influenza; and
- a cluster of (e.g. >3) patients with healthcare facility-acquired influenza-like
illness are identified on the same floor or ward during a short (eg. 48-72 hour)
period.
- Consider daily monitoring for influenza-like illness in selected settings, especially
on wards with particularly vulnerable patients, such as intensive care units, oncology
units, and other "sentinel" floors.
- Evaluate whether infection control measures (eg. droplet precautions) are properly
instituted for influenza-positive patients, and investigate whether the infection
was acquired in the community or while hospitalised.
The Flu Vaccine
The vaccines available in Australia are prepared from purified inactivated influenza virus.
Immunisation with available vaccines provides 70-90% protection against infection
with the antigens present in the vaccine in healthy young adults. It is however
less effective at preventing disease in the elderly, but may still prevent hospitalisation,
and modify the illness and it’s complications. In a recent study, vaccination
of the elderly against influenza was associated with reductions in the risk of hospitalisation
for heart disease, cerebrovascular disease, and pneumonia or influenza as well as
the risk of death from all causes during influenza seasons.
The vaccine components are altered biannually to reflect the strains of influenza
that have been identified circulating worldwide in the previous months. The available
vaccines confer protection for about a year, and should be given each year prior
to the flu season (April to September in Australia). However, the vaccine is ideally
given in autumn, in anticipation of winter outbreaks.
The influenza vaccine can be administered concurrently with other vaccines, and
protection from vaccination is usually achieved within 10-14 days.
Contraindications to vaccination include egg protein allergy, previous anaphylactic
reactions to influenza vaccine components, acute febrile illnesses, or a history
of Guillain-Barre Syndrome related to influenza vaccination.
Which Staff and Patients should be
Vaccinated
The influenza vaccine is recommended annually for all healthcare workers. Other
persons (including household members) in close contact with persons at high risk
should also be vaccinated to decrease the risk for transmitting influenza to persons
at high risk (for example; residential care staff).
The following patients should be vaccinated:
- Patients 65 years of age and older.
- All Aboriginal and Torres Strait Islander people aged 50 years and older, and those
aged 15-49 years with underlying medical conditions
- Residents of nursing homes and long-term care facilities
- Patients > 6 months and under 65 years of age with chronic medical conditions:
- Congenital heart disease
- Congestive heart failure
- Coronary artery disease
- Diabetes
- Chronic lung disease (including cystic fibrosis and bronchiectasis)
- Chronic renal failure
- Immunosuppression (including HIV-infected patients)
- Smoking
Influenza vaccine is recommended for pregnant women who will be in the second or
third trimester during the influenza season, and there is no evidence of it causing
congenital malformations if given in the first trimester.
Influenza vaccine can be given to children as young as 6 months, however there is
an increased risk of adverse events.
Research has shown that influenza vaccination of healthy working adults younger
than 65 years can reduce the rates of influenza-like illnesses, lost workdays, and
physician visits during years when the vaccine and circulating viruses are similar.
However, there may not be proven economic benefits to this strategy in every year
as the amount of circulating influenza varies.
Test your Knowledge - Exercise 1
Clicking the above link will take you to the Education Resources page where you can download a PDF version of the Exercises Questions and Answers
Further Information
References
- National health and medical research council. The Australian Immunisation handbook 2003, 8th edition.
- Bridges CB. Thompson WW. Meltzer MI. Reeve GR. Talamonti WJ. Cox NJ. Lilac HA. Hall
H. Klimov A. Fukuda K. Effectiveness and cost-benefit of influenza vaccination of
healthy working adults: A randomized controlled trial. JAMA 2000;284(13):1655-63
- Nichol KL. Nordin J. Mullooly J. Lask R. Fillbrandt K. Iwane M. Influenza vaccination
and reduction in hospitalizations for cardiac disease and stroke among the elderly.
New England Journal of Medicine, 2003; 348(14):1322-32.