Flu vaccine: who is eligible, types, side effects and timing

The vaccine trains your immune system to recognise the most common circulating flu viruses before you meet them. The NHS is careful about expectations: there is still a chance you could get flu after being vaccinated, but it is likely to be milder and not last as long.

Because it is the type of vaccine that cannot cause flu, any aches or low temperature afterwards are an immune reaction rather than an infection. The NHS says the injected vaccines for adults contain no live flu viruses.

It protects only against flu. It will not stop colds, Covid-19 or other winter respiratory infections, although the NHS notes you can have the flu vaccine at the same time as other vaccines such as Covid-19 and shingles.

The free NHS adult vaccine is aimed at people at higher risk of serious illness. The NHS page lists the following groups, and advises that anyone with a health condition who is unsure of eligibility should check with their GP surgery or specialist.

• Aged 65 or over, including those who turn 65 by 31 March 2027.

• Aged 18 to 64 with certain long-term health conditions.

• Pregnant, at any stage of pregnancy.

• Living in a care home.

• The main carer for an older or disabled person, or receiving a carer's allowance.

• Living with someone who has a weakened immune system.

• Aged 16 or over and sleeping rough or staying in a hostel or night shelter.

• Frontline health and social care workers, who are vaccinated through their employer.

The NHS says the vaccine is recommended for people with a range of long-term conditions. The table groups them as the NHS page does. It is a summary, not a complete clinical rule, and a GP or specialist can confirm whether a particular diagnosis counts.

Children are offered the vaccine for two reasons given by the NHS: flu can cause serious problems such as pneumonia, with thousands of children who have no health condition needing hospital care each winter, and children catch and spread it easily, so vaccinating them also protects babies, pregnant women and older people.

For the current season the NHS says it is recommended for children aged 2 or 3 years on 31 August 2026, children aged 4 who have not started school, school-aged children from reception to year 11, and children from 6 months to 17 years with certain long-term conditions. Most school-aged children are vaccinated at school, usually in the autumn term.

Most children receive a nasal spray into each nostril, which the NHS describes as quick and painless and as the preferred vaccine for ages 2 to 16. An injection is used instead for children under 2 and for those who cannot have the spray, for example after a severe reaction to a previous dose, with a severely weakened immune system, or following a recent asthma flare-up. The spray contains porcine gelatine, and a gelatine-free injection is available for families who do not want it.

Adults receive an injection, and the product depends on age. The NHS lists adjuvanted, cell-based, high-dose and recombinant vaccines for those aged 65 and over, and cell-based and recombinant products for younger adults, with a further option if the first choice is not available. Sixteen- and seventeen-year-olds may be offered the nasal spray or a cell-based injection.

You do not need to choose. The NHS says that if you are eligible you will be offered the type most appropriate for you, and the patient information leaflets list the ingredients if you want to check them.

The NHS says the common side effects of the injected vaccines are mild and settle within 1 to 2 days: pain or soreness where the injection was given, a slightly raised temperature and an aching body. The nasal spray can cause a blocked or runny nose, loss of appetite, tiredness and headache. Serious allergic reactions are very rare, and vaccinators are trained to treat them.

The only people who cannot have the vaccine are those who previously had a severe allergic reaction to a dose or an ingredient. If you have a high temperature the advice is to wait until you feel better, and a very blocked or runny nose may mean a child has to wait for the spray or is offered an injection.

Studies have shown the vaccine is safe at any stage of pregnancy, according to the NHS, and it helps protect a baby for the first few months after birth. It is safe to breastfeed after having it.

Vaccination is organised every year, usually from autumn. For adults the NHS lists GP surgeries, pharmacies offering the free vaccine and, for some people, maternity services, care homes or employers. Online booking is available through the NHS website and the NHS App.

Protection takes up to 14 days to build, so earlier in the season gives longer cover before flu is widely circulating. Dates and eligibility are reviewed each year, so the current NHS page is the reference for the season you are in.