The government has announced that it is widening its free winter flu vaccination programme in England.
Last year, around 15 million people received the jab, which protects against seasonal flu.
However, officials hope this will rise to 30 million this winter as it extends the scheme to include a broader range of people.
So, who is eligible for the vaccine now and just how effective is it? Here is everything you need to know.
Watch: What is the difference between an antigen and antibody test?
What is the flu vaccine?
Flu circulates every winter and generally peaks in December and January. This means that many people often get ill around the same time.
To prevent overwhelming demand on the NHS, people most at risk of problems if they catch flu are offered a vaccination against the virus to help protect them.
Who normally gets the flu vaccine?
Typically, the flu vaccine is routinely given on the NHS to:
adults 65 and over
people with certain medical conditions (including children in at-risk groups from six months of age)
children aged 2 and 3
children in primary school
frontline health or social care workers
Who is eligible under the new extension?
This year, around 30 million people are to be offered the free flu vaccine with many becoming eligible for the very first time.
The new extensions will include all over-50s, as well anyone on the shielding list and the people they live with.
We're expanding eligibility for the flu vaccination programme.— Department of Health and Social Care (@DHSCgovuk) July 24, 2020
More info on who can now get it:
This expansion is part of our plan to protect the NHS this winter. You can help by getting a flu vaccination if eligible.#VaccinesWork | #ValueofVaccines
Also for the first time, children in their first year of secondary school will all be offered the vaccine.
Plans for Scotland, Wales and Northern Ireland are yet been announced.
Why is it being extended this year?
The government has decided to increase the number of people eligible for the vaccine to prepare for a winter that could see the annual flu season coincide with a surge in coronavirus.
The move comes following concerns about the impact an increase in Covid-19 cases and seasonal could have on the NHS.
How does the flu vaccine work?
According to the NHS, the flu vaccine stimulates your body's immune system to make antibodies to attack the flu virus.
Antibodies are proteins that recognise and fight off germs, such as viruses, that have invaded your blood.
If you're exposed to the flu virus after you have had the flu vaccine, your immune system will recognise the virus and immediately produce antibodies to fight it.
It may take 10 to 14 days for your immunity to build up fully after you have had the flu vaccine.
You will also need to have a flu vaccination every year as the antibodies that protect you from flu decline over time, and flu strains can also change from year to year.
Where can you get the flu vaccine?
You can have your NHS flu vaccine at your GP surgery, a local pharmacy offering the service or your midwifery service, if they offer it for pregnant women.
Some community pharmacies now offer flu vaccination to adults (but not children) at risk of flu, including pregnant women, people aged 65 and over, people with long-term health conditions and carers.
If you have your flu vaccine at a pharmacy, you do not have to inform a GP. It is down to the pharmacist to do that, the NHS says.
How effective is it?
Flu vaccine is the best protection we have against the unpredictable.
The NHS states that studies have shown that the flu vaccine will help prevent you getting the flu. However, it will not stop all flu viruses and the level of protection may vary, so it is not a 100 per cent guarantee that you will be flu-free.
If you do get flu after vaccination, it is likely to be milder and shorter-lived than it would otherwise have been.