"I managed to avoid covid-19 for almost four years," tweeted TV presenter Mehdi Hasan two weeks ago.
"But he finally grabbed me. At the end of 2023."
Hasan added that his symptoms are fortunately mild, but he is only one of many who reported the first positive test for the virus responsible for the pandemic, Sars-CoV-2, four years since it began to spread around the world.
The number of covid-19 infections is starting to jump again as a result of the covid variant JN.1, which first appeared last September in France.
The variant is responsible for about 60 percent of new infections in early January, according to a data tracker from the US Centers for Disease Control and Prevention (CDC).
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At the same time, data from both the CDC and the British Health Security Agency show that the number of hospitalizations and deaths from covid-19 is significantly lower compared to January 2023.
Primary care doctors say it's almost impossible for them to distinguish the symptoms of covid-19 from the flu without the help of a PCR test.
"When covid first appeared, it was characterized by very unusual, vague symptoms - from brain fog, exhaustion and loss of sense of taste and smell," says Ziad Tukmachi, a general practitioner at Chartfield practice in south-west London.
"Now I get the impression that it has mutated to much more flu-like symptoms, where it's much harder to tell them apart clinically."
What are the symptoms of subvariant JN.1
The version of the covid-19 virus behind the latest spike in infections shares many symptoms with earlier variants of Sars-CoV-2: sore throat, fatigue, headache and cough.
Differences in symptoms often depend on the previous state of health and the immune system of the infected person.
But some clinicians report that among the most common first signs of JN.1 infection are diarrhea or headache.
Fewer patients lose their sense of smell in the near-omicron variants, of which JN.1 is a subvariant.
And while all of this might suggest that the virus is evolving to become less pathogenic, epidemiologists believe the reality on the ground is more complex than that.
"The virus is not necessarily less pathogenic," says Greg Towers, professor of molecular virology at University College London.
"Instead, it infects a population that is less prone to the disease, because it has already encountered Sars-CoV-2 before, and is better at regulating the immune response to it."
Towers says that the main lesson during the pandemic is that the symptoms that appear in patients are highly dependent on their previous immune status.
In the first two years of covid-19, the reactions of individual patients to the virus were primarily dictated by the state of their immune health, along with previous exposure to other corona viruses.
Today, in 2024, that is determined by a much more complex cocktail of factors, including how many times a person has been infected with the virus, their vaccination status, and whether their vaccine-induced immunity is waning.
As a result, Dennis Nash, an epidemiologist at the City University of New York, says that people who now get Covid-19 for the first time are more at risk, especially if it's been a long time since their last booster shot.
"There are still people who have somehow managed to stay completely free of covid," says Nash.
"If they are unvaccinated or undervaccinated, they could be most at risk of severe and prolonged symptoms."
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However, Sars-CoV-2 is constantly mutating, which also subtly changes the ways it tries to enter the human body.
The JN.1 variant has an increased ability to evade the immune system, for example, compared to other omicron subvariants.
But it also changes the way it affects the human body.
In 2023, researchers from the Virginia Commonwealth University School of Medicine reported that people who now become infected with omicron subvariants have only a 6-7 percent chance of losing their sense of taste or smell, compared to infections with the virus in the early stages of the covid-19 pandemic.
Instead, some clinicians such as David Strain, associate professor of cardiometabolic health at the University of Exeter in the UK, told the BBC that his patients were more likely to have diarrhea or headaches after contracting the JN.1 or EG.5 variants. .
"There's a huge shift in viral tropism, which means which cells get infected," says Towers.
“And that's governed by the spike protein sequence. Almost everyone in the world has been infected or vaccinated, so the virus is under enormous pressure to avoid those immune responses in order to continue to be transmitted, so the spike protein has evolved a lot.
"This causes it to infect other cells to get in, which is why people no longer lose their sense of smell or taste."
Researchers are still trying to understand whether some of the more subtle, internal consequences of Sarsa-CoV-2 infection vary between virus variants, or whether the differences are more driven by the waning of prior vaccine protection.
One ongoing concern remains the virus' ability to cause damage in blood vessels and internal organs through the formation of microclots, while the kidney, an organ made up of roughly a million tiny blood vessels called capillaries, appears particularly vulnerable based on the patients Strain has seen.
"These are just observations, but with the new JN.1 variant, we're seeing more microvascular complications and significant changes in kidney function that seem worse than in several previous variants," says Strain.
"But it's hard to say whether it's the variant or the fact that it's been 18 months to two years since many people last received the vaccine."
With some new evidence suggesting that microclots can cause long-lasting covid.
An August 2023 study even suggested that they could be contributing to the cognitive problems experienced by many long-term Covid patients, and researchers now worry that we could be in for another spike in chronic cases.
However, it would be difficult to distinguish whether this is a consequence of a new variant or a decline in immunity in the population.
"Studies from March to summer 2020 show that the risk of Long-lasting Covid from any one case was about 10 percent," says Danny Altman, professor of immunology at Imperial College London.
"Now we have many more infections, and the risk of Long-term covid seems to have decreased, not because of the milder variant but because of the degree of protection from vaccine doses.
"A study in the BMJ of a national cohort in Sweden shows that protection increases with each subsequent dose."
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All of this points to the continued importance of all groups staying up-to-date with vaccine boosters, but while politicians have long been eager to move away from covid, Strain says it's critical to continue monitoring how different variants continue to infect us.
"The symptoms really change from variant to variant," he says.
"We had periods when the earliest symptom was a headache and others when it was more gastrointestinal. We all want to go back to normal life, but the reality is that covid is not going anywhere."
what happened with 'covid thumbm'?
In the early months of the covid-19 pandemic, reports began to emerge of an unusual and confusing symptom of the disease - patients began to develop painful lesions on their feet and hands that itched unbearably.
These frostbite-like swellings and redness of the skin became known as "covid thumb".
Doctors and scientists were puzzled - how could a respiratory virus cause such an unusual symptom in the body's extremities?
Tests on samples taken from people with covid thumb failed to show the presence of the virus responsible for covid-19, Sars-CoV-2, in frostbite, suggesting that the virus itself is not directly responsible.
Instead, a number of hypotheses have been put forward, including that it may be the result of an overreaction of a part of the immune system that produces a protein called interferon IFN-1, which helps the immune system target virus-infected cells.
Others have suggested that it is not something specific to covid-19 at all, but just a reaction that occurs in people who are otherwise prone to frostbite.
A third theory is that quarantine rules have meant that more people simply don't wear adequate footwear at home and spend too much time sitting still.
Unusually, with the development of the virus and the lifting of the quarantine, the occurrence of these skin problems also disappeared.
Research by scientists at King's College London, UK, who looked at symptoms in more than 348.000 people who reported them via a mobile phone app, found that covid thumb and related skin problems have declined in recent waves of the Sars-Cov-virus. 2.
They were reported by 11 percent of people during the wave caused by the omicron strain, as opposed to 17 percent during the wave of the delta strain, during which symptoms also tended to last longer.
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