What is influenza and how is it different from a cold?

Influenza (flu) is a respiratory infection caused by influenza viruses (types A, B, C and D). Unlike the common cold, influenza typically causes sudden onset of high fever (38-40°C), severe myalgia (muscle aches), fatigue, headache and respiratory symptoms. The systemic features — particularly fever and myalgia — are much more pronounced than in colds. Influenza is also significantly more dangerous: it causes 290,000-650,000 deaths per year globally.

Why does the flu vaccine change every year?

Influenza viruses mutate rapidly through a process called antigenic drift, gradually changing their surface proteins so that previous immunity becomes less effective. WHO's GISRS monitors circulating strains worldwide and issues twice-yearly recommendations (for Northern and Southern hemisphere seasons) on which virus strains the vaccine should target. Because the virus evolves, last year's vaccine may not protect well against this year's dominant strain.

Who should get the flu vaccine?

WHO recommends annual influenza vaccination as a high priority for: adults aged 65 and older; pregnant women (at any stage of pregnancy); children aged 6 months to 5 years; people with chronic medical conditions (heart disease, diabetes, lung disease, immunosuppression); and all healthcare workers. These groups face the highest risk of severe disease and death. Vaccination of healthcare workers also protects vulnerable patients.

How effective is the flu vaccine?

When the vaccine strains are well-matched to circulating viruses, influenza vaccination reduces the risk of illness by 40-60%. In seasons with poor match it may be lower. Even a less well-matched vaccine provides meaningful protection against severe illness and death, particularly in older adults and those with chronic conditions. Annual vaccination is recommended regardless of the previous year's coverage because immunity wanes over time.

What is H5N1 avian influenza and why is it concerning?

H5N1 is a highly pathogenic avian influenza virus that has circulated in bird populations globally since 1997. It does not easily spread between humans, but when it does infect people it carries a case fatality rate of approximately 60% in detected cases. Since 2024, H5N1 has spread to dairy cattle in the United States, with dozens of human cases — mostly in farm workers. This raises pandemic preparedness concerns because cattle provide a new potential reservoir for human exposure and viral adaptation.

What is pandemic influenza and how is it different from seasonal flu?

Pandemic influenza occurs when a novel influenza A subtype emerges against which humans have little or no pre-existing immunity and which can spread efficiently person-to-person. Major 20th century pandemics: 1918 (Spanish flu, H1N1, ~50 million deaths), 1957 (H2N2), 1968 (H3N2). The 2009 H1N1 pandemic was moderate in severity but spread globally within weeks. Pandemic preparedness — surveillance, vaccine prototype development, stockpiling of antivirals, national response plans — is a core function of WHO's GISRS.

What is the difference between influenza A and B?

Influenza A viruses can infect both humans and animals (birds, pigs, horses, seals, cattle) and are the only type capable of causing pandemics through reassortment. Influenza B infects mainly humans and causes seasonal epidemics but not pandemics. Both A and B are included in seasonal influenza vaccines. Influenza C causes mild, infrequent respiratory illness; influenza D primarily affects cattle.

What is the WHO GISRS network?

The Global Influenza Surveillance and Response System (GISRS) is one of the oldest and most sophisticated global disease surveillance systems — established in 1952 and now spanning over 150 national influenza centres in 114 countries. It collects and analyses thousands of influenza specimens weekly, identifies novel and drug-resistant strains, tracks H5N1 and other pandemic threats, and provides the evidence base for WHO's semi-annual vaccine strain recommendations. GISRS was a model for COVID-19 surveillance responses.

What is a universal influenza vaccine?

A universal influenza vaccine would target conserved parts of the influenza virus that do not change with annual mutation — such as the stalk domain of haemagglutinin, the M2 ion channel or internal proteins. It would eliminate the need for annual reformulation, provide broader protection across subtypes and ideally confer more durable immunity. Multiple candidates are in clinical development. A universal vaccine would also substantially improve pandemic preparedness against novel influenza strains.

What happened in the 1918 influenza pandemic?

The 1918-1919 influenza pandemic — caused by an H1N1 virus — is the deadliest infectious event in recorded history, killing an estimated 50-100 million people (more than 2.5% of the world population) in approximately 12 months. Unusually, it disproportionately killed young healthy adults. The 1918 pandemic demonstrated both influenza's pandemic potential and the catastrophic consequences of poor healthcare access, overcrowding and delayed public health responses — lessons directly relevant to COVID-19 and H5N1 preparedness.

How does GMJ News cover influenza?

GMJ News follows WHO GISRS vaccine strain recommendations, H5N1 avian influenza developments, antiviral trial results and influenza vaccination policy. Georgia's influenza vaccination coverage and disease burden are topics of ongoing relevance to the Georgian Medical Journal and PHIG's public health surveillance work.

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Influenza

Q: How is influenza treated?

Most healthy adults recover from influenza without specific treatment, with rest and symptomatic management. Antivirals — oseltamivir (Tamiflu) and baloxavir (Xofluza) — reduce illness duration by approximately 1-2 days and reduce the risk of complications when started within 48 hours of symptom onset. They are most important for high-risk groups (older adults, children under 2, pregnant women, immunocompromised patients) and hospitalised patients. Antibiotics are not effective against influenza and should not be prescribed unless bacterial superinfection occurs.

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Seasonal influenza causes about 1 billion infections every year, including 3–5 million severe cases and 290,000–650,000 respiratory deaths (WHO) — a toll the annual vaccine, updated twice yearly through WHO's 70-year-old Global Influenza Surveillance and Response System (GISRS), keeps in check but never eliminates. The larger shadow is pandemic risk: H5N1 avian influenza has spread through wild birds, poultry and — since 2024 — dairy cattle, with sporadic human cases keeping virologists on alert. Vaccination of health workers, older adults, pregnant women and the chronically ill remains the core defence GMJ News monitors, alongside zoonotic surveillance.

Key messages

Annual burden

Seasonal influenza causes approximately 1 billion infections, 3-5 million severe cases and 290,000-650,000 respiratory deaths every year worldwide (WHO).

Vaccine works

The annual influenza vaccine reduces the risk of illness by 40-60% when well-matched to circulating strains. WHO recommends vaccination for high-risk groups: older adults, pregnant women, healthcare workers, children 6 months-5 years and people with chronic conditions.

GISRS surveillance

WHO's Global Influenza Surveillance and Response System (GISRS) — 70+ years old — monitors circulating strains in real time across 114 countries, informing twice-yearly vaccine strain recommendations for Northern and Southern hemisphere seasons.

Pandemic threat

Influenza A viruses can reassort to produce novel pandemic strains. H5N1 avian influenza has spread globally through wild birds and poultry and, since 2024, dairy cattle — with sporadic human cases raising pandemic preparedness alert levels.

Treatment

Antivirals — primarily oseltamivir (Tamiflu) and baloxavir — reduce severity and duration of influenza when started within 48 hours of symptom onset. They are most critical for hospitalised patients and high-risk groups.

Universal flu vaccine

A universal influenza vaccine — targeting conserved viral proteins that do not change with annual mutation — is a major research priority that would eliminate the need for annual reformulation and improve pandemic preparedness.

Key statistics

infections/year (seasonal)

WHO

290-650K

respiratory deaths/year

WHO

3-5M

severe cases/year

WHO

114

countries in GISRS

WHO

40-60%

vaccine efficacy when well-matched

CDC/WHO

H5N1

avian flu in dairy cattle since 2024

WHO/CDC

Estimated seasonal influenza-associated respiratory deaths/year by WHO region (thousands)

Source: Iuliano et al., Lancet 2018. Estimates have wide uncertainty ranges reflecting surveillance gaps.

Glossary of key terms

Influenza A
WHOOne of the four types of influenza virus — the only type capable of causing pandemics through reassortment of genes between human and animal strains. Subtypes are classified by surface proteins H (haemagglutinin) and N (neuraminidase). Seasonal H1N1 and H3N2 currently circulate.

Antigenic drift
WHOGradual accumulation of mutations in influenza surface proteins that allows the virus to partially escape existing immunity. The primary reason influenza vaccines must be updated annually.

Antigenic shift
WHOA sudden, major change in influenza A surface proteins, typically through reassortment of gene segments between human and animal strains. Produces novel subtypes against which human populations have little or no immunity — the mechanism of pandemic influenza emergence.

GISRS
WHOGlobal Influenza Surveillance and Response System — WHO's 70+-year-old network of over 150 national influenza centres in 114 countries. Monitors circulating strains year-round to inform vaccine strain selection for both hemispheres.

Oseltamivir
WHO EML/FDAAn antiviral medicine (Tamiflu) that inhibits influenza neuraminidase, reducing viral replication. Reduces illness duration by approximately 1 day and hospitalisation risk in high-risk groups when started within 48 hours. On the WHO Essential Medicines List.

H5N1
WHO/OIEA highly pathogenic avian influenza subtype that has circulated in bird populations since 1997. Since 2024, H5N1 has spread to dairy cattle in multiple US states with sporadic human cases. The case fatality rate in detected human cases is approximately 60%, raising pandemic preparedness concerns.