Influenza Surveillance
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Influenza Surveillance

​​In Malta, sentinel surveillance of Influenza activity in the community has been underway since 2003. The main objectives of a sentinel surveillance system are to: 

  • Estimate the proportion of primary health encounters with Influenza
  • Describe aspects of the epidemiology of Influenza at GP level
  • Obtain data which contributes to Influenza prevention and control by identifying trends
  • Obtain information on circulating viral strains of Influenza

Sentinel surveillance study involves a number of voluntary general practitioners who report on Influenza activity in their practice including Influenza like-illness (ILI) and acute respiratory infection (ARI).

A case of Influenza-like illness is defined as a person presenting to the general practitioner with sudden onset of symptoms and at least one of the following symptoms: fever or feverish, malaise, headache, myalgia and at least one of the following three respiratory symptoms: cough, sore throat and shortness of breath.

Acute respiratory infection is defined as as a person presenting to the general practitioner with sudden onset of symptoms and at least one of the following four symptoms: cough, sore throat, shortness of breath and coryza. The definition comprises common cold but not rhinitis and sinusitis. 

A number of problems are encountered in trying to perform sentinel surveillance at community level in Malta since:

  • Patients are not registered to a particular GP and can therefore go to different GPs  in private or public practice
  • Most GPs  do not have existing registers of their patients list so their patient population is not known. To overcome this problem, an idea of the burden of illness can be obtained from the proportion of Influenza cases seen out of the total number of the primary health encounters. In fact each participating GP reported on the total number of health encounters seen at his practice for any reason during each reporting week. This was used as the denominator in estimating the proportion of Influenza cases over the total number of the primary health encounters.

Participating GPs were provided with specific forms to report on Influenza cases. Information on cases includes age, gender, vaccination status and requests for virological testing. Each of the GPs also gave details of age and gender of patients seen at their practice over the same period for any condition in order to describe the primary health encounters in their practice. Throat or nasal swabs are taken by the GP which are then sent to the Virology Department at St. Lukes Hospital where they are analysed for Influenza A and B viruses.

The proportion of Influenza Like Illness of the primary health encounters  is calculated using the number of reported  cases (in accordance with the specified case definition) as the numerator, while the total number of health encounters of participating GPs during the study period was used as the denominator. 
The graph shows the number of primary health encounters with Influenza Like Illness per 1000 primary health encounters during the Influenza season from October till May for 3 Influenza seasons ( 2014-2015, 2015-2016,  2016-2017 )


                                                                                                                                                                                        What is influenza?
Influenza is an acute illness of the respiratory tract caused by influenza viruses. It can be caused by various types of influenza viruses. Influenza can occurs throughout the year, but is usually more common in periods from January to March/April in the Northern hemisphere. The virus mainly spreads by respiratory droplets. The disease is characterised by fever, sore throat, cough, runny nose, headache, muscle aches and general tiredness. It is usually self-limiting with recovery in two to seven days. However, if persons with weakened immunity and elderly persons get infected, it can be a serious illness and may be complicated by bronchitis, pneumonia, encephalopathy, or even death in the most serious cases. Serious infection or complications can also occur in healthy individuals

Why is seasonal influenza vaccination important?
Seasonal influenza vaccination is one of the most effective means to prevent seasonal influenza and its complications, as well as reduce influenza related hospitalisation and death.
There is increasing evidence suggesting that a person getting influenza and COVID-19 at the same time may be more seriously ill and has a higher risk of death, and influenza vaccination may reduce the likelihood of hospitalisation and length of stay. 

Who should have higher priority for seasonal influenza vaccination?
People who are in the priority groups are generally at increased risk of severe influenza or transmitting influenza to those at high risk. Therefore, they should have higher priority for seasonal influenza vaccination.
In the 2021-22 season, the Advisory Committee on Immunisation Policy (ACIP) recommends the following priority groups for seasonal influenza vaccination:

Persons aged 55 years and over
Children from 6 months to 11 years
Healthcare workers 
Residents of Residential Care Homes and Institutions
Persons with chronic medical problems:
    o Chronic disease of the heart, lung, liver, kidneys and neurological systems
    o Chronic asthma
    o Diabetes
    o Immunosuppressive states through illness or treatment – including HIV
    o Persons suffering from isolated hypertension do not fall in the priority group.

Who should not receive the influenza vaccine?
People who have a history of severe allergic reaction to any vaccine component or a previous dose of any influenza vaccine are not suitable to have the seasonal influenza vaccination. 
Individuals with mild egg allergy who are considering an influenza vaccination can be given the flu vaccine in primary care setting. Individuals with a history of anaphylaxis to egg should have seasonal influenza vaccine administered by healthcare professionals in appropriate medical facilities with capacity to recognise and manage severe allergic reactions.
If an individual suffers from fever on the day of vaccination, vaccination should be deferred till recovery.

What are the possible side effects following influenza vaccine administration?
Inactivated influenza vaccine is very safe and usually well tolerated apart from occasional soreness, redness or swelling at the injection site. 
Some people may experience fever, muscle pain, and tiredness beginning 6 to 12 hours after vaccination and lasting up to two days. The fever and muscle pain may be controlled with the use of paracetamol.
Immediate severe allergic reactions like hives, swelling of the lips or tongue, and difficulties in breathing are rare and require emergency consultation.

Does seasonal influenza vaccine cause influenza?
The viruses in the influenza vaccine are killed viruses, therefore the vaccine cannot cause influenza. 

s the seasonal influenza vaccine safe for pregnant and breastfeeding mothers?
Yes. Seasonal influenza vaccine is safe for pregnant and breastfeeding mothers. Women who receive the influenza vaccination while pregnant or breastfeeding can develop antibodies against influenza that can be passed to their infants through their breast milk and provide some protection against influenza for infants.

Does the seasonal influenza vaccine contain a mercury compound?
No. The influenza vaccines currently supplied for use in the EU does not contain a mercury compound (e.g. thiomersal).

Does the seasonal influenza vaccine work right away?
No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. For prevention against influenza, vaccinated individuals should maintain good personal and environmental hygiene practices, balanced diet, regular exercise, adequate rest and no smoking.

Is it necessary to get vaccinated against seasonal influenza every year?
Yes. The circulating seasonal influenza strains may change from time to time. In accordance with the circulating strains, the seasonal influenza vaccine composition is updated every year to enhance protection. The immunity built up in a vaccinated person in the prior season will decrease over time and may become too low to provide protection in the next season. In addition, the vaccine compositions of the 2021-22 seasonal influenza vaccine are different from those in 2020-21 season.

Can the pneumococcal vaccine be given together with seasonal influenza vaccine?
Yes. Pneumococcal vaccine can be given with seasonal influenza vaccine at the same clinic visit, but should be administered with a different syringe and at a different injection site. 

Can COVID-19 vaccine be given together with seasonal influenza vaccine?
Yes. The third dose of the Covid-19 vaccine can be given at the same time as the influenza vaccine but using a different injection site. If a person has not had any Covid vaccine prior to the influenza vaccine, then a period of 14 days must elapse before administration of the Covid or any other vaccine.

Why do some people who have been vaccinated with seasonal influenza vaccine still get influenza / influenza-like illness?
There are several reasons why someone may get influenza / influenza-like illness even after they have been vaccinated. Firstly, because the body takes about 2 weeks to develop antibodies after vaccination. If a person is infected with influenza virus shortly after vaccination, he or she may develop influenza before becoming immune. Secondly, infection of viruses other than influenza virus can also result in illness similar to influenza, so people may falsely think that they had influenza despite being vaccinated. Thirdly, small number of people experience side effects after receiving inactivated influenza vaccine, for example fever and myalgia, which may be confused with influenza virus infection. Lastly, the vaccine is unable to provide complete protection against influenza, because vaccine effectiveness depends on factors including the similarity between the virus strains present in the vaccine and those circulating in the community, as well as the characteristics of recipients, for example, age. 

Should everyone receive the seasonal influenza vaccine?
All members of the public except those with known contraindications should receive the influenza vaccine annually because influenza vaccination is one of the most effective means in reducing the risk of influenza and its complications together with reduction in influenza-associated hospitalisation and death.


 Flu News Europe