If you feel unwell with a bad throat and a temperature you may well have caught one of the new strains of Covid circulating this autumn.
XFG, called Stratus by some, and NB.1.8.1, known as Nimbus, are now the most common variants being passed around in the UK, according to officials.
Experts say these do not appear to pose any bigger threat than previous types of Covid or make people feel more ill.
But recent genetic changes the virus has acquired may make infections more likely.
It is usual for viruses to evolve as they spread between people over time. When the changes become significantly different, the new virus types are known as variants.
According to some reports, there may be tell-tale symptoms with the latest ones - a hoarse voice or a "razor blade" sore throat.
Covid can still cause a wide range of symptoms, including headache, coughing, a blocked or running nose and exhaustion, making it difficult to distinguish from a cold or flu.
If you think you have Covid you should avoid contact with vulnerable people and stay at home if possible.
If you have symptoms and need to leave the house, advice remains that you should wear a face covering. Washing hands regularly and using and disposing tissues in bins can reduce the spread of this and other respiratory illnesses.
For a sore throat, drinking plenty of fluids and having a teaspoon of honey may help, the NHS says.
According to the Royal College of GPs, rates of Covid are now increasing across the UK, especially in the very young and elderly.
Hospital admissions linked to Covid are also going up.
People over 75 can get a free vaccine against Covid on the NHS. This can offer good protection, even against the new variants, says the UK Health Security Agency (UKHSA).
It is urging people to book their vaccinations against flu and another common winter virus called RSV (respiratory syncytial virus) as cases start to increase ahead of winter.
"It's normal for viruses to mutate and change, and as more data becomes available on these variants, we'll have a better understanding of how they interact with our immune systems and how to optimise our protection, as well as actions we can take to keep the most vulnerable safe and live our lives as normally as possible," says the UKHSA.
"The most important thing is for those eligible to get their vaccination when it is due."
It's possible to catch Covid again even if you have had it very recently, or have been vaccinated. Reinfections are usually mild, but you can feel unwell and still spread the virus to others.
Covid tests are no longer widely available for free, but pharmacies still sell them.
A number of High Street chemists and private clinics sell Covid vaccines too. The cost varies, with some charging around £99 for a single dose.