Influenza: Prevention and Reducing the Risk of Complications

Influenza remains one of the most predictable and, at the same time, most underestimated causes of seasonal illness and death. Last season, 216 childhood deaths were recorded in the United States—the highest number in 15 years, reflecting declining vaccination coverage and high viral circulation. This is not a localized news item, but a signal of risks for any healthcare system. [1]

The primary line of defense is annual vaccination. It is recommended by all key health authorities, and the vaccine formulations are adjusted annually to meet expected strains. For the Northern Hemisphere, annual recommendations are established by the World Health Organization. This is the foundation of prevention and the most effective way to reduce the risk of severe illness and death. [2]

European countries are focusing on priority groups, but the trend is toward expanding coverage and eliminating access gaps. Particular attention is given to pregnant women, the elderly, people with chronic diseases, and young children. Vaccination rates vary greatly between countries and social groups, and low coverage among vulnerable people is associated with worse outcomes. [3]

Vaccination is not the only measure. Layers of non-pharmacological interventions, such as clean indoor air, hand hygiene, and respiratory hygiene, complement protection. Scientific reviews emphasize that the evidence for individual measures outside of healthcare settings is mixed, but a comprehensive approach reduces transmission. Updated guidelines on indoor air quality offer guidance on air exchange and filtration as part of the epidemic response strategy. [4]

Vaccination in the new season: what's new and what's important

In the 2025-2026 season, all seasonal vaccines are trivalent. For egg-based vaccines, components similar to A H1N1 of pandemic origin "A Victoria 4897 2022", A H3N2 "A Croatia 10136RV 2023", and B Victoria "B Austria 1359417 2021" are recommended. This reflects an update based on the results of global surveillance and antigen mapping. [5]

The optimal time is early autumn, before intense virus circulation, but it makes sense to get vaccinated at any time while viruses are circulating in the community. The immune response takes approximately two weeks to develop, so waiting until the peak of the season is not recommended. [6]

Egg allergies are no longer a reason to delay vaccination: no additional precautions beyond those required for any vaccination are required. Any age-appropriate and health-appropriate vaccine, including egg-based vaccines, can be used. It is important that the vaccination site be prepared to recognize and treat rare acute reactions. [7]

Combining with other vaccinations is acceptable. For most people, influenza, COVID-19, and respiratory syncytial virus vaccines can be administered in a single visit, based on current indications and availability. This is logistically convenient and increases coverage. For immunocompromised patients, combining the two is also acceptable, taking into account individual risks and specialist recommendations. [8]

Table 1. Composition of seasonal vaccines 2025-2026 (Northern Hemisphere)
Source of composition - regulatory decisions for the 2025-2026 season.

Component	Description of the strain declared for selection
A H1N1	"A Victoria 4897 2022"
A H3N2	A Croatia 10136RV 2023
In Victoria	"To Austria 1359417 2021"
[9]

Who should get vaccinated first?

The basic rule is simple: annual vaccination is recommended for all people starting at 6 months of age, unless there are contraindications. This reduces the risk of severe illness, hospitalization, and death in all age groups, and also protects others by reducing transmission. [10]

Priority is given to groups at increased risk of severe outcomes. These include people 65 years and older, patients with chronic lung, heart, and metabolic diseases, immunodeficiencies, pregnant women, young children, and healthcare workers. In European countries, the lists of risk groups are similar and are gradually expanding. [11]

High-dose or adjuvanted MF59-based vaccines have been shown to provide better protection against complications in the elderly compared to the standard dose. Relative effectiveness is reflected in fewer hospitalizations due to cardiorespiratory events and confirmed cases of influenza. [12]

During pregnancy, vaccination is safe and effective, reducing the risk of laboratory-confirmed influenza in the mother and indirectly protecting the infant during the first months of life. Studies from recent seasons show comparable efficacy in pregnant and non-pregnant women, supporting active immunization strategies. [13]

Table 2. For whom vaccination is especially important and why

Group	Reason for priority	Peculiarities of vaccine selection
65 years and older	High risk of hospitalization and death	Consider high-dose or adjuvant
Chronic diseases	Risk of decompensation and complications	Standard inactivated ones are suitable for most people
Pregnant women	Maternal protection and passive protection of the infant	Inactivated, by terms - all year round with circulation
Children under 5 years old	High morbidity and complications	Age-specific schedules, sometimes 2 doses are required
[14]

Which vaccine to choose?

There are several types. There are inactivated injectable vaccines, including those based on cell culture and recombinant technologies, as well as adjuvanted and high-dose options for older people. A separate option is a live attenuated nasal spray for healthy people of certain ages. [15]

For older adults, it's reasonable to opt for high-dose or adjuvanted drugs: they generate a stronger immune response and, in some studies, offer better protection against severe outcomes. Specific availability varies by country and season, but the recommendation to "look for enhanced forms" remains valid. [16]

The nasal spray has limitations. It is not used during pregnancy, in immunocompromised individuals, in certain chronic respiratory conditions, or in individuals with certain anatomical conditions. Before use, it is important to undergo standard contraindication screening and consult current recommendations. [17]

A new convenience this season is the approval of self-administration of nasal sprays by adults and parental administration to children, subject to instructions and storage conditions. This could improve accessibility in households and hard-to-reach areas, although practical implementation depends on logistics. [18]

Table 3. Comparison of the main types of vaccines

Type	Pros	Cons	Who is it usually recommended for?
Inactivated standard	Wide availability	The older people have a more modest response.	Most adults and children
Inactivated high dose	The best protection is in the elderly	Less available	65 years and older
Adjuvanted	Strengthening the immune response	Local reactions are more common	65 years and older, subject to availability
Recombinant or cellular	Technological advantages	Availability by region	Alternative for special indications
Live nasal spray	Without injection	There are contraindications	Healthy people of certain ages
[19]

Timing, dosage and regimens

The best time is early autumn. But if you missed it, get vaccinated as soon as possible, while virus circulation is still being recorded in the region. The effect takes two weeks to develop, so an early start gives you a head start before the surge in cases. [20]

Children aged 6 months to 8 years who are receiving the vaccine for the first time or have an incomplete history may require two doses, separated by 4 weeks. This is recommended for seasonal periods and is important for developing an adequate immune response at younger ages. [21]

Dosages and age restrictions vary between specific medications. Consult the instructions and national calendars: manufacturers produce versions in disposable syringes and multi-dose vials for different ages. Medical documentation always specifies the injection volumes for each age group. [22]

A mild cold without a high fever does not interfere with vaccination, but if you have a severe fever, vaccination is usually postponed until you feel better. This is a general safety rule for any vaccination, helping to avoid the overlap of illness symptoms and post-vaccination reactions. [23]

Table 4. Typical dosages and regimens by age.
These are specified according to the instructions for a specific drug and the national calendar.

Age	Basic scheme for the season	Volume per injection	Are 2 doses needed for primary vaccination?
6-35 months	Inactivated	0.25-0.5 ml according to the instructions	Yes
3-17 years old	Inactivated or nasal spray as indicated	0.5 ml or 0.2 ml for spray	Sometimes, based on vaccination history
18-64 years old	Inactivated	0.5 ml	No
65 years and older	High-dose or adjuvant	0.5 ml	No
[24]

Chemoprophylaxis: When are antiviral drugs appropriate before illness?

Antiviral drugs do not replace immunoprophylaxis and are not generally used for everyone. Chemoprophylaxis is indicated on a targeted basis: in cases of close contact with an infected person within a family or community, in long-term care homes, in people at high risk of severe illness, and during outbreaks in institutions. The decision is made by a physician, taking into account the timing of exposure and viral circulation. [25]

The drugs of choice are oseltamivir, inhaled zanamivir, and baloxavir. Oseltamivir and zanamivir are administered in courses, while baloxavir is given as a single dose. Indications and age limits vary by country and specific approval. In Europe, baloxavir is approved for post-exposure prophylaxis, while oseltamivir is registered for both treatment and prophylaxis. [26]

Timing is critical: it's best to begin treatment within the first 48 hours after exposure. Treatment typically lasts 5-10 days for household contacts, and at least 14 days in closed communities, up to a week after the outbreak ends. Baloxavir is conveniently administered as a single dose when prescribed promptly. [27]

Inhaled zanamivir is not suitable for people with severe bronchial obstruction. Age limits and dosages for oseltamivir depend on body weight, while for baloxavir, they depend on age and weight. In the European Union, a very young age is permitted for the post-exposure regimen for specific indications. All decisions are made only after an in-person risk assessment. [28]

Table 5. Chemoprophylaxis: who, when and how much

Preparation	When to start	Duration	Who is it suitable for?	Comments
Oseltamivir	Up to 48 hours after contact	5-10 days	For adults and children by body weight	For outbreaks in institutions, it may take longer
Zanamivir	Up to 48 hours after contact	10 days	Selectively, in the absence of broncho-obstruction	Inhalation form
Baloxavir	Up to 48 hours after contact	One time	Adolescents and adults, in the EU - extended indications	Convenient to follow the scheme
[29]

Non-pharmacological measures: air, behavior, habits

Clean indoor air is a strategic measure. Updated recommendations indicate a target of at least five air exchanges per hour, the possibility of using high-efficiency filters and ultraviolet disinfection technologies as part of a "package" of engineering solutions. This reduces aerosol concentrations and the overall risk of infection. [30]

Masks and respirators are appropriate primarily in healthcare settings and when a person exhibits symptoms as a "source control" measure. Outside of healthcare settings, the evidence is mixed, and large reviews emphasize that "masks as a stand-alone intervention" produce inconsistent results, while a combination of measures is more effective. [31]

Hand hygiene remains a basic habit with proven effectiveness, especially when combined with other measures. School and family clusters have shown reduced disease incidence with regular handwashing and use of alcohol-based hand rubs, especially when the intervention is accompanied by education. [32]

Simple organizational steps can reduce the burden on the healthcare system: staying home during acute illness, separating outpatient clinics, raising public awareness, and improving air quality in classrooms and offices as a standard. European guidelines for public health measures incorporate these approaches into preparedness plans. [33]

Table 6. Practical measures outside of medicine: where the effect is greater

Measure	Where it is especially useful	Commentary on effectiveness
Air exchange is not below the benchmarks	Schools, offices, clinics	Aerosol load reduction, combined with filtration
Filtration and ultraviolet	High density areas	Enhances the ventilation effect
Masks for symptoms	Medical facilities, public places during outbreaks	Source control is the most justified
Hand hygiene	All teams	Works better as part of a complex
[34]

Mistakes, myths, and current debates

The common myth that "vaccines cause the flu" has long been debunked: inactivated vaccines do not contain live virus, and expected reactions such as aches and pains and low-grade fever are related to the development of an immune response. Weighing the risks always favors vaccination, especially in high-risk groups. [35]

Discussions surrounding preservatives periodically flare up in the media, but the scientific community finds no reason to believe they cause harm when used as directed. Political decisions by some authorities in certain countries in 2025 have drawn criticism from experts due to the risk of limiting the availability of multi-dose formulations. When developing clinical recommendations, it is advisable to be guided by the evidence base and vaccine availability. [36]

Declining vaccination coverage is directly linked to an increase in severe outcomes, including in children. Seasonal reports confirm: the fewer people vaccinated, the greater the burden on hospitals, the higher the mortality rate, and the higher the risk of outbreaks in groups. This is the first controllable factor that can be effectively influenced. [37]

A practical algorithm for families and teams: schedule vaccinations now, improve indoor air quality, agree on "stay home if you show signs of infection" guidelines, organize access to hand sanitizer and soap and water, and maintain a plan for vulnerable family members in case of exposure, including discussing chemoprophylaxis with a doctor. This "layered" approach reduces personal and societal risks. [38]

Application

Should I get vaccinated if I had the flu last season?
Yes, because immunity is highly specific, and strains and the antigen profile of the season change. Furthermore, protection diminishes over time. [39]

Can pregnant women receive the vaccine?
Yes. Inactivated vaccines are safe and effective at all times, as long as the virus is circulating in the region. This also protects the baby during the first months of life. [40]

What if you're allergic to eggs?
That's not a problem. Any suitable vaccine can be used; no special precautions are required other than being prepared for rare reactions. [41]

What to do after close contact at home?
Contact a doctor within the first 48 hours to assess the need for chemoprophylaxis. Oseltamivir, zanamivir, or baloxavir may be considered, depending on age, weight, and contraindications. [42]