The World Health Organization (WHO) issued its 2026-2027 northern hemisphere flu vaccine composition recommendation on February 27, 2026, after reviewing global surveillance data. WHO holds these consultations twice a year, once for each hemisphere, because circulating influenza viruses continue to change.

WHO asks countries to base influenza vaccination programs on local disease burden, epidemiology, cost-effectiveness and delivery capacity. Its March 2026 guidance recommends annual vaccination for higher-risk groups before the local influenza season. Eligibility, product choice, funding and calendar dates remain national or regional decisions.

Breathing difficulty after vaccination needs emergency care

The US Centers for Disease Control and Prevention (CDC) lists hives, swelling of the face or throat and difficulty breathing as signs of a possible severe allergic reaction after flu vaccination. Breathing difficulty, collapse or symptoms that worsen rapidly require immediate help from the emergency service where the person is located.

The same US CDC page lists soreness, redness or swelling at the injection site, headache, fever, fatigue and muscle aches among possible reactions. Persistent, worsening or otherwise concerning symptoms need clinical assessment rather than an assumption that every symptom is expected.

A person rolls up a sleeve to receive an influenza vaccine in a clinic (illustrative image)

Annual vaccination covers two moving targets

The US CDC gives two reasons for yearly vaccination: immune protection declines over time, and vaccine composition is reviewed as circulating viruses change. A dose recorded in a previous season therefore does not replace the current recommendation in the country where vaccination takes place.

WHO says national vaccine regulators and manufacturers use its composition recommendations to develop, produce and authorize vaccines for the following influenza season. The process aims for a close match with viruses expected to circulate, but it cannot predict every virus that will spread.

Infection after vaccination does not establish that the dose failed

The US CDC says vaccinated people can still get influenza if exposure occurs before protection develops, if the infecting virus differs from those in the vaccine, or if age or health affects the immune response. Symptoms alone also cannot confirm that an illness was influenza rather than another respiratory infection.

The US CDC's evidence summary finds that vaccination can reduce flu-related hospitalization and severe outcomes among people admitted with influenza. The estimates differ by season, virus, age group and outcome, so the evidence does not support one fixed effectiveness percentage or a claim about what would have happened to one person.

Egg allergy is not a blanket bar under US guidance

Under US CDC guidance, people with egg allergy may receive any egg-based or non-egg-based flu vaccine that is otherwise appropriate for their age and health, without precautions beyond those used for every vaccination. All vaccination settings still need staff and equipment able to recognize and treat an acute allergic reaction.

The US CDC distinguishes egg allergy from a previous severe reaction to a flu vaccine or another vaccine component, which can rule out a product or require a separate assessment. Product ingredients, authorization and clinical guidance must be checked in the country where the vaccine would be given.

Vaccination timing follows local influenza activity

WHO says temperate regions in the northern and southern hemispheres have different influenza seasons, while tropical regions can have one or more periods of increased activity during year-round circulation. WHO advises vaccination just before the local influenza season rather than during one fixed month worldwide.

WHO says it can take up to two weeks after vaccination for the body to develop protective antibodies. That interval supports planning before the local rise in transmission, but it is not a promise of complete protection on a particular day.

Pregnancy, childhood and chronic illness require separate checks

WHO asks countries to consider health workers, people with underlying conditions, older adults and pregnant people as priority groups, while children remain an important group under national program goals. The recommendation guides public programs and does not create one product or dose schedule for every person.

US CDC clinical guidance says the number of doses and product choice depend on age, vaccination history and the vaccine used, and that pregnancy changes which formulation is used in the United States. Children, pregnant people, those with chronic conditions and people taking medicines that affect immunity need the current local schedule and a clinician who knows their history.

Same-day vaccination depends on the products

WHO says an inactivated seasonal influenza vaccine and a COVID-19 vaccine may be given during the same visit. That position does not settle every vaccine combination, so other same-day plans depend on the products and the applicable national guidance.

Records and local rules determine the next step

A vaccination review needs the date and product for previous flu doses, any severe reaction to a vaccine or its ingredients, age, pregnancy status, chronic conditions and medicines that affect immunity. The vaccinating service can then apply the current schedule, authorized products and timing used in that country.

APPI News did not verify authorization, supply, price or public coverage in every market at the time of writing. Those details can change between seasons even when countries draw on the same WHO composition recommendation.

Frequently asked questions

Why is flu vaccination offered every year?
Immune protection declines, while circulating influenza viruses and the recommended vaccine composition change. WHO recommends annual vaccination before the local influenza season for higher-risk groups, while national programs set eligibility.

Can influenza occur after vaccination?
Yes. Protection varies, but public-health evidence supports lower risks of hospitalization and severe outcomes in studied populations; one infection cannot show what the outcome would have been without vaccination.

Does egg allergy rule out flu vaccination?
Not under current US CDC guidance, which allows any otherwise appropriate egg-based or non-egg-based vaccine without extra measures for egg allergy alone. A previous severe reaction to a flu vaccine or another component is a separate issue that needs clinical review.

Which month is best for vaccination?
There is no worldwide month. WHO advises vaccination just before the local influenza season, including in regions where circulation is year-round or has multiple periods of increased activity.

Can a flu vaccine be given with another vaccine?
WHO accepts giving an inactivated seasonal influenza vaccine with a COVID-19 vaccine during the same visit. Other combinations depend on the products and local guidance.