With flu season setting in across countries, including the US and the UK, doctors are urging people to get their annual flu shots. October offers an opportunity to build protection before winter flu activity increases.The UK Health Security Agency (UKHSA) reported above-average flu activity and urged at-risk groups to get vaccinated. England's flu vaccination program last winter is estimated to have prevented about 100,000 hospital admissions and 7,000 deaths.The US Centers for Disease Control and Prevention (CDC) recommends annual flu vaccination for everyone aged six months and older. The seasonal vaccine targets influenza A(H1N1), A(H3N2) and B/Victoria viruses.In September, the Indian Medical Association (IMA) also highlighted annual influenza vaccination and gaps in adult immunization.Why Is October A Good Time To Get Vaccinated?Also read: Flu Activity Rises Early In US, UK And Japan: Why Experts Urge Vaccination Before WinterThe flu vaccine takes about two weeks to build protection, making October a good time to get vaccinated before winter, Dr. Bhawna Malik, Senior Consultant-Neonatologist and Pediatric Intensivist at Motherhood Hospitals, Greater Noida, told HealthandMe.In India, flu activity can increase between January and March. Vaccination in October allows time for immunity to develop before this period.However, October is not the only option. Dr. Vikas Maurya, Senior Director and HOD, Pulmonology, Fortis Hospital, Shalimar Bagh, told HealthandMe that vaccination can also be taken between April and mid-June, ahead of another period of flu activity from July to September.He said one dose annually is generally sufficient, with timing depending on local flu patterns and the vaccine used.Who Should Get The Flu Vaccine?Healthy adults and children, as well as people with underlying conditions, can benefit from flu vaccination. Influenza can cause pneumonia, hospitalization and other severe complications.Older adults, particularly those aged 65 and above, and people with diabetes, heart disease, kidney or liver disease, asthma or chronic obstructive pulmonary disease (COPD) face a higher risk of complications.“Flu vaccination doesn't protect just yourself against the risk of having influenza but it also prevents transmission of infection to other vulnerable people around ourselves like little ones, elderly family members and people with medical conditions,” Dr. Malik said.Dr. Mohit Bhardhwaj, Consultant, Pulmonology, PB Health, Gurugram, told HealthandMe that annual vaccination helps protect individuals and reduce transmission, as flu viruses change and vaccine protection can decrease over time.Flu Vaccine Schedule For Children And AdultsRead More: Flu 2026: Symptoms To Watch For As New Season BeginsThe vaccine can be administered from six months of age. The schedule depends on age and previous vaccination history.Children aged six months to eight years: Some children receiving the vaccine for the first time need two doses at least four weeks apart.Children aged nine and above: Annual vaccination is generally recommended.Adults: One dose each flu season is generally recommended.Infants younger than six months: Cannot be vaccinated directly.Dr. Malik recommends vaccination for parents, siblings and caregivers to help reduce the risk of transmitting influenza to infants who are too young to receive the vaccine.Are There Any Side Effects? Most flu vaccine side effects are mild and may include injection-site pain, redness or swelling, fever, headache, body aches and tiredness. These generally settle within a few days, Dr. Bhardhwaj said.A cooling pack or an ice pack wrapped in cloth may help relieve injection-site discomfort. Nasal vaccines may cause a stuffy nose, cough or headache, Dr. Maurya noted.The injected flu vaccine cannot cause influenza. Anyone experiencing persistent fever, breathing difficulty or unusual symptoms should seek medical advice. Those with a history of serious allergic reactions to a previous flu vaccine should consult their doctor before vaccination.