How Covid-19's symptoms have changed with each new variant

With a new variant of the Sars-CoV-2 virus causing a spike in cases, it is demonstrating just how much the disease has changed since the pandemic began – and what happened to "Covid toe". "For almost four years, I've managed to dodge Covid-19," TV broadcaster Mehdi Hasan tweeted a fortnight ago. "But it finally got me. At the end of 2023." Hasan added that his symptoms were thankfully mild, but he is just one of many people reporting their first ever positive test for the virus responsible for the pandemic, Sars-CoV-2, four years on from when it first began spreading around the world. What are the symptoms of JN.1 and KP.2 The version of the Covid-19 virus behind the latest spike in infections shares many of the same symptoms as earlier variants of Sars-CoV-2 : a sore throat, fatigue, headache and a cough. Differences in the symptoms often depend on a person's underlying health and their immune system. But some clinicians are reporting among the most common first signs of an infection by JN.1 are diarrhoea or a headache. Fewer patients are losing their sense of smell with variants closely-related to Omicron, of which JN.1 is a subvariant. Another Omicron subvariant, KP.2 shares many genetic features with JN.1, but shows two distinctive mutations in its spike protein, leading to the nickname "FLiRT" as a way of describing specific amino acid changes. Although KP.2 has a higher reproductive number than JN.1, suggesting it is more transmissible, the virus itself has been found to be up to 10 times less infectious. It's symptoms are said to be similar to those experienced with other Omnicron variants. Covid-19 cases are starting to rise again as a result of the KP.2 Covid subvariant, which was first reported on 2 January but started to become the dominant version of the virus in many countries in May 2024. By 13 May 2024, it accounted for 28% of cases in the US. It follows a rise in cases earlier in the year due to the JN.1 Covid subvariant, which appeared last September in France. This subvariant accounted for around 60% of new infections in early January, according to a data tracker from the US Centers for Disease Control and Prevention (CDC). At the same time, data from both the CDC and the UK Health Security Agency shows that hospitalisations and deaths from Covid-19 are markedly lower compared to May 2023. Primary care physicians say they are finding it virtually impossible to distinguish Covid-19 symptoms from influenza without the help of a PCR test. "When Covid first came, it was characterised by these very odd, vague symptoms – from brain fog, feeling exhausted, and losing taste and smell," says Ziad Tukmachi, a GP at Chartfield Surgery in south-west London, UK. "Now I feel it's mutated to more similar symptoms to the flu, where it's very difficult clinically to distinguish between the two." While this might all suggest that the virus is evolving to become progressively less pathogenic, epidemiologists believe that the reality of the situation is more nuanced. "The virus isn't necessarily less pathogenic," says Greg Towers, professor of molecular virology at University College London, UK. "Rather, it's infecting a population that are less inclined to become sick, because they've seen Sars-CoV-2 before, and they're better at regulating [their] immune response against it."