With millions urged to get vaccines against COVID-19 and the flu ahead of a potential 'twindemic' this winter, it's important to be aware of the symptoms of each virus.

There will be lower levels of natural immunity to flu this year after we've been less exposed to other people during the pandemic, UK Health Security Agency (UKHSA) officials have warned.

And of course, unfortunately, COVID-19 is still in circulation, though we are far more prepared for it.

“This winter could be the first time we see the effects of the so-called ‘twindemic’ with both Covid and flu in full circulation, so it is vital that those most susceptible to serious illness from these viruses come forward for vaccines in order to protect themselves and those around them," said NHS director for vaccinations and screening Steve Russell at the end of September.

And following the warning, last week experts said that flu season appears to have arrived early, urging people again to get a jab. Monitoring by the UKHSA suggests cases have risen across England, with more calls to NHS 111, as well as a slight rise in people seeking help from their GP for symptoms.

Signs for both COVID-19 and the flu are very similar, and can be hard to distinguish between. But, while you should try to stay home and avoid infecting others regardless, here's a look at how each virus might present in you.

Read more: Flu jab: Who's eligible for the NHS vaccine rollout and how to book

Flu symptoms

The flu is a contagious respiratory disease caused by influenza viruses. Similarly to COVID-19, it is spread by droplets from when an infected person coughs, sneezes or talks.

Flu symptoms, according to the NHS include:

• a sudden high temperature

• an aching body

• feeling tired or exhausted

• a dry cough

• a sore throat

• a headache

• difficulty sleeping

• loss of appetite

• diarrhoea or tummy pain

• feeling sick and being sick

While flu will often get better on its own, some can get seriously ill, which is why it's important to protect yourself with the NHS vaccine if you're advised to.

Symptoms present similarly in children, though they can get pain in their ear and seem less active too.

Read more: How to spot if a cough is coronavirus or hay fever

Covid symptoms

COVID-19 is also a contagious respiratory illness, but is caused by the SARS-CoV-2 virus, a form of coronavirus.

As per the NHS, symptoms include:

• a high temperature or shivering (chills)

• a new, continuous cough

• a loss or change to your sense of smell or taste

• shortness of breath

• feeling tired or exhausted

• an aching body

• a headache

• a sore throat

• a blocked or runny nose

• loss of appetite

• diarrhoea

• feeling sick or being sick

These are thought to be similar between adults and children.

The NHS added nine new COVID-19 symptoms to the list in April, following the original signs of infection that consisted of just 'fever', 'new continuous cough', and 'loss of sense of smell or taste'.

However, thanks to analysis of daily reports from users on the ZOE COVID study app, it has been able to identify the top five symptoms in order, in a report last updated on 20th October. They are also different depending on how many vaccinations you've had.

Read more: Nearly 90% of immunocompromised patients generate some antibody response after two coronavirus jabs

Covid symptoms after two vaccinations

1. Sore throat

2. Runny nose

3. Blocked nose

4. Persistent cough

5. Headache

ZOE points out that previous 'traditional' symptoms like anosmia (partial or full loss of smell), shortness of breath and fever rank lower down on the list.

Covid symptoms after one vaccination

1. Headache

2. Runny nose

3. Sore throat

4. Sneezing

5. Persistent cough

Covid symptoms with no vaccinations

1. Headache

2. Sore throat

3. Runny nose

4. Fever

5. Persistent cough

Read more: Signs and symptoms you've got flu

In a World Health Organization (WHO) Science in 5 video last October, Dr Sylvie Briand stated: "So the flu is very common, especially in the season, and usually the symptoms are fever, headache and muscle ache, but also upper respiratory symptoms such as sneezing and coughing.

"For COVID-19 it's the same symptoms basically, but in addition, we have specific symptoms such as anosmia, which is a lack of smell and ageusia, which is a lack of taste. And many people, especially young people, have experienced these additional and specific symptoms for COVID-19."

She added, "But sometimes people have very few symptoms, whether it's for flu or for COVID-19. It really depends on your level of immunity."

While it's not listed under 'flu symptoms', elsewhere the NHS website does acknowledge that changes in sense of smell can also be caused by the flu, as well as a cold, sinusitis, an allergy or growths in your nose.

The UKHSA on gov.uk, currently states, "The symptoms of COVID-19 and other respiratory infections are very similar. It is not possible to tell if you have COVID-19, flu or another respiratory infection based on symptoms alone. Most people with COVID-19 and other respiratory infections will have a relatively mild illness, especially if they have been vaccinated."

If you have the flu, rest and sleep, keep warm, take paracetamol or ibuprofen and drink plenty of fluids. Ask for an urgent GP appointment or call NHS 111 if any of the following apply – you or your child have symptoms of flu and you're worried about your baby's or child's symptoms, you're 65 or over, you're pregnant, you have a long-term medical condition, you have a weakened immune system or your symptoms don't improve after seven days.

If you have COVID-19 symptoms, call NHS 111 if you're feeling worried or unsure what to do, or you're worried about a baby or child under five.

For either, try to stay at home and avoid contact with other people if you have a high temperature or do not feel well enough to do your normal activities (taking extra care to avoid those at high risk).

Call 999 or go to A&E if you get sudden chest pain, have difficulty breathing, start coughing up a lot of blood, or your child seems very unwell, is getting worse or you think there's something seriously wrong.

For more information see the NHS website on the flu or or COVID-19.

Watch: COVID-19: Autumn booster and flu jabs to be extended to over 50s to reduce hospital admissions