December 1, 2023


The value of truth

Influenza (Seasonal)

7 min read

Essential info

  • There are all-around a billion instances of seasonal influenza each year, which include 3–5 million conditions of extreme ailment.
  • It results in 290 000 to 650 000 respiratory fatalities on a yearly basis.
  • Ninety-9 % of deaths in kids underneath 5 yrs of age with influenza-associated decreased respiratory tract bacterial infections are in building nations.
  • Symptoms start off 1–4 times just after infection and commonly past around a week.


Seasonal influenza (the flu) is an acute respiratory an infection caused by influenza viruses. It is popular in all pieces of the planet. Most people recover with out therapy.

Influenza spreads very easily amongst people when they cough or sneeze. Vaccination is the best way to avoid the sickness.

Indicators of influenza involve acute onset of fever, cough, sore throat, body aches and exhaustion.

Treatment method must aim to reduce symptoms. Folks with the flu should rest and drink a good deal of liquids. Most people will get well on their very own inside of a 7 days. Professional medical treatment may possibly be essential in serious situations and for men and women with hazard elements.

There are 4 types of influenza viruses, styles A, B, C and D. Influenza A and B viruses circulate and induce seasonal epidemics of ailment.

  • Influenza A viruses are more labeled into subtypes according to the mixtures of the proteins on the floor of the virus. Now circulating in humans are subtype A(H1N1) and A(H3N2) influenza viruses. The A(H1N1) is also created as A(H1N1)pdm09 as it induced the pandemic in 2009 and changed the prior A(H1N1) virus which had circulated prior to 2009. Only influenza variety A viruses are identified to have brought about pandemics.
  • Influenza B viruses are not labeled into subtypes but can be broken down into lineages. Influenza kind B viruses belong to possibly B/Yamagata or B/Victoria lineage.
  • Influenza C virus is detected considerably less usually and typically results in moderate infections, hence does not present public overall health relevance.
  • Influenza D viruses largely have an effect on cattle and are not regarded to infect or cause sickness in persons.

Symptoms and indicators

Indications of influenza usually start out about 2 times following becoming infected by somebody who has the virus.

Symptoms include things like:

  • sudden onset of fever
  • cough (normally dry)
  • headache
  • muscle mass and joint soreness
  • intense malaise (experience unwell)
  • sore throat
  • runny nose.

The cough can be critical and can previous 2 weeks or extra.

Most people recover from fever and other symptoms inside of a 7 days without necessitating healthcare consideration. Nonetheless, influenza can result in extreme disease or death, in particular in persons at large chance.

Influenza can worsen signs or symptoms of other continual diseases. In extreme circumstances influenza can guide to pneumonia and sepsis. Men and women with other professional medical problems or who have significant signs should search for medical treatment.

Hospitalization and loss of life because of to influenza take place largely amid superior-chance teams.

In industrialized international locations most fatalities connected with influenza take place amongst people today aged 65 a long time or more mature (1).

The effects of seasonal influenza epidemics in producing international locations are not entirely regarded, but analysis estimates that 99% of deaths in youngsters under 5 many years of age with influenza connected reduce respiratory tract bacterial infections are in creating nations (2).


All age groups can be affected but there are teams that are much more at threat than other people.

  • Persons at increased chance of extreme disorder or troubles when infected are expecting females, children underneath 5 years of age, more mature folks, people today with long-term professional medical disorders (this kind of as persistent cardiac, pulmonary, renal, metabolic, neurodevelopmental, liver or hematologic health conditions) and people today with immunosuppressive situations (this sort of as HIV, obtaining chemotherapy or steroids, or malignancy).
  • Wellness and care employees are at substantial possibility of buying influenza virus an infection thanks to increased exposure to the clients, and of even further spreading especially to susceptible men and women. Vaccination can safeguard overall health employees and the persons all around them.

Epidemics can final result in high concentrations of employee/college absenteeism and productivity losses. Clinics and hospitals can be overcome in the course of peak illness intervals.


Seasonal influenza spreads quickly, with rapid transmission in crowded spots including faculties and nursing homes. When an contaminated human being coughs or sneezes, droplets containing viruses (infectious droplets) are dispersed into the air and can infect individuals in shut proximity. The virus can also be spread by palms contaminated with influenza viruses. To protect against transmission, people today should address their mouth and nose with a tissue when coughing and clean their palms consistently.

In temperate climates, seasonal epidemics happen generally all through wintertime, although in tropical areas, influenza may possibly manifest in the course of the calendar year, creating outbreaks additional irregularly.

The time from infection to ailment, known as the incubation period, is about 2 times, but ranges from 1–4 times.


Most situations of human influenza are clinically identified. Nonetheless, throughout durations of small influenza exercise or outdoors of epidemics circumstances, the infection of other respiratory viruses (e.g. SARS-CoV-2, rhinovirus, respiratory syncytial virus, parainfluenza and adenovirus) can also existing as influenza-like disease (ILI), which tends to make the medical differentiation of influenza from other pathogens difficult.

Assortment of ideal respiratory samples and the software of a laboratory diagnostic take a look at is necessary to establish a definitive analysis. Appropriate selection, storage and transportation of respiratory specimens is the critical initial phase for laboratory detection of influenza virus bacterial infections. Laboratory affirmation is commonly done making use of immediate antigen detection, virus isolation, or detection of influenza-precise RNA by reverse transcriptase-polymerase chain reaction (RT-PCR). A variety of steering on the laboratory methods is posted and current by WHO.

Rapid diagnostic tests are employed in medical options, but they have decrease sensitivity in comparison to RT-PCR solutions and their reliability depends largely on the situations under which they are utilised.


Most folks will get well from influenza on their personal. Men and women with extreme signs or symptoms or other health-related circumstances must look for professional medical treatment.

People with mild symptoms should really:

  • remain residence to stay clear of infecting other people
  • rest
  • consume lots of fluids
  • handle other indicators these kinds of as fever
  • look for professional medical treatment if signs get worse.

Persons at high threat or with intense signs or symptoms ought to be treated with antiviral remedies as before long as probable. They incorporate people today who are:

  • expecting
  • kids underneath 59 months of age
  • aged 65 yrs and older
  • residing with other continual diseases
  • acquiring chemotherapy
  • living with suppressed immune systems thanks to HIV or other circumstances.

The WHO International Influenza Surveillance and Reaction Process (GISRS) displays resistance to antivirals among circulating influenza viruses to deliver timely proof for national insurance policies linked to antiviral use.


Vaccination is the most effective way to stop influenza.

Protected and helpful vaccines have been employed for additional than 60 years. Immunity from vaccination goes away above time so yearly vaccination is recommended to guard from influenza.

The vaccine may perhaps be a lot less efficient in more mature people, but it will make the ailment less extreme and reduces the chance of difficulties and death.

Vaccination is specially vital for individuals at high chance of influenza complications and their carers.

Once-a-year vaccination is advised for:

  • expecting females
  • little ones aged 6 months to 5 years
  • persons over age 65
  • individuals with serious clinical disorders
  • wellness staff.

Other techniques to reduce influenza:

  • wash and dry your palms often
  • deal with your mouth and nose when coughing or sneezing
  • dispose of tissues accurately
  • stay residence when experience unwell
  • steer clear of shut contact with ill men and women
  • avoid touching your eyes, nose or mouth.


Vaccines are updated routinely with new vaccines made that contain viruses that match those people circulating. Several inactivated influenza vaccines and recombinant influenza vaccines are available in injectable form. Reside attenuated influenza vaccines are offered as a nasal spray.

WHO reaction

WHO, by way of the World Influenza Programme and GISRS, in collaboration with other companions, continuously displays influenza viruses and action globally, suggests seasonal influenza vaccine compositions twice a 12 months for the northern and southern hemisphere influenza seasons, guides countries in tropical and subtropical regions as to which formulation vaccines to use, supports conclusions for timing of vaccination campaigns, and supports Member States to acquire avoidance and control approaches.

WHO will work to strengthen countrywide, regional and international influenza response capacities which includes diagnostics, antiviral susceptibility monitoring, condition surveillance and outbreak reaction, to enhance vaccine protection between substantial-chance teams, and to assist research and advancement of new therapeutics and other countermeasures. 

1. Estimates of US influenza-connected deaths created making use of 4 different methods.
Thompson WW, Weintraub E, Dhankhar P, Cheng OY, Brammer L, Meltzer MI, et al. Influenza Other Respi Viruses. 20093:37-49

2. International load of respiratory bacterial infections due to seasonal influenza in younger children: a systematic critique and meta-analysis.
Nair H, Abdullah Brooks W, Katz M et al. Lancet 2011 378: 1917–3