New Year’s Eve gatherings, drinks with the neighbours: with zero restrictions on mixing, and almost three years of catching up to do, it’s perhaps no surprise that many of us have been struck down with a mysterious lurgy that causes fever, sore throat, headache and other decidedly Covid-like symptoms – perhaps more than once.
But if you are consistently testing negative for Covid on a lateral flow test, what else could it be? And are we really more vulnerable to getting sick this winter, or have we just forgotten what life was like before Covid restrictions stopped the usual merry-go-round of seasonal infections?
December 2022 has been party season not only for humans but for influenza, metapneumovirus, RSV and all manner of other bugs that spread through snot, respiratory droplets, and sloppy kisses under the mistletoe.
Covid continues to circulate, with a 22% increase in hospital admissions recorded in England between 7 and 14 December. Dr Stephen Griffin, a virologist at the University of Leeds, said: “The difficulty is that we don’t have freely available PCR tests any more, and a lot of people who are vaccinated [against Covid] don’t necessarily show up on LFTs if they are infected.”
Testing several times as your illness progresses may be the only way to rule out Covid – and even then you may never know for sure. But although Covid may be the first thing we think of when we feel seriously unwell, it is by no means the only bug capitalising on the heady pre-Christmas cocktail of social events.
Prof Kamila Hawthorne, the chair of the Royal College of GPs, said: “Figures from the college’s research and surveillance centre show that rates of influenza-like illnesses, respiratory conditions and the common cold have been rising – and we are currently seeing cases of strep, tonsillitis and upper respiratory infections above the seasonal average.”
The biggest problem at the moment is flu. The number of patients in hospital with flu has risen 79% in the past week, according to new data. An average of 3,746 people with flu were in hospital across the seven days to 25 December, up from 2,088 the previous week, according to NHS England.
The winter of 2017-18 was a really bad flu season, with the highest number of excess winter deaths recorded in England and Wales in more than 40 years – although below-average temperatures may also have contributed.
“This year’s flu season started earlier than in 2017, and it seems to be tracking a similar kind of trajectory, with cases still going up,” said Dr Antonia Ho, a consultant in infectious diseases and clinical senior lecturer at the MRC-University of Glasgow Centre for Virus Research.
Flu can be severe, even in younger, healthy people. “It can be like a bad cold, but it can also be drenching night sweats, really severe joint pains, and older people in particular are vulnerable to pneumonia,” Ho said.
“Another dangerous thing is that flu, in particular, predisposes to secondary bacterial infections. A lot of the group A strep that is currently circulating in children is probably linked to preceding respiratory virus infections.”
Indeed, the UK also experienced higher than usual numbers of scarlet fever and invasive strep A infections after the 2017-18 flu season.
Current data suggest that the main strain of influenza circulating in the UK is H3N2, which tends to be associated with more severe disease, particularly in vulnerable groups such as elderly people and young children. The current flu vaccine broadly covers this strain, but even during seasons when most circulating flu viruses are well matched to the vaccine strains, vaccination only reduces the risk of flu illness by between 40% and 60%.
Although uptake of the seasonal flu vaccine among adults has been similar to the last couple of years, uptake among children has been lower, with just a third of two- to three-year-olds having been vaccinated by late November; typically, children receive their vaccine through a nasal spray. At present, about 650 children under five are in hospital with flu in England, roughly 44% more than at same time in 2019-20.
However, influenza isn’t the only virus doing the rounds that can cause flu-like symptoms. Infections with respiratory syncytial virus (RSV) are higher than normal, and, although babies and young children are at greater risk of hospitalisation and death, RSV can also trigger symptoms such as a bad cough and fever in adults.
“There was a big peak of rhinovirus not long ago, and then you have things like metapneumovirus, parainfluenza and seasonal coronaviruses,” said Griffin. “Upper respiratory tract viruses, such as rhinoviruses, tend to be associated with a runny nose, but everyone responds differently so it’s really hard to symptomatically define which respiratory virus you’ve got.”
Like influenza, most of these viruses peak during winter, as they replicate faster and stay infectious for longer when it is cold. Exposure to cold air also reduces the innate immune defences in our noses, making it easier for us to be infected with airborne viruses, and we are exposed to more of them when we spend more time socialising indoors.
Two years of barely being exposed to such bugs appears to have disrupted their usual patterns. Typically, a certain number of people will get infected each year, due to immunity from past exposure wearing off in adults, and a fresh batch of young children never having encountered them before. But if these seasonal waves are suppressed, for example due to school closures and restrictions on mixing, then the number of susceptible individuals in a population will increase – particularly if vaccine uptake for some of these viruses is low.
Now that people are mixing more, wearing masks less and paying less attention to ventilation and vigilant hand hygiene, opportunities for these susceptible individuals to be infected – and to pass these infections on – are great.
This does not mean that we should routinely try to get infected with such viruses to keep our immune systems strong. Ho said: “The fact that some kids are encountering a lot of these bugs later on is not necessarily a bad thing. For example, a lot of kids under the age of one have real breathing difficulties with RSV. The fact that they won’t have encountered it during their first year of life is probably a good thing, because they will now have a more mature immune system that’s better able to deal with it.”
A further complication is that some people may be infected with more than one virus – or a virus and a bacteria – at the same time. According to a study of hospital patients published in the Lancet earlier this year, those who tested positive for Sars-CoV-2 and influenza were more likely to require mechanical ventilation, or to die, compared with those who only had Covid. Patients who were co-infected with Sars-CoV-2 and an adenovirus – another virus that can cause common cold or flu-like symptoms – were also at greater risk of death.
The likelihood of viral co-infections may be greater this winter, because various respiratory viruses appear to be peaking at the same time, rather than sequentially as happened pre-pandemic. “In a normal year, RSV would tend to peak before Christmas, and then flu would happen around Christmas or just afterwards. Now we’ve also got Sars-CoV-2 happening at the same time, so a lot of things are different,” Griffin said.
The good news is that many of these illnesses are preventable, through good public hygiene such as regular handwashing, throwing tissues away once they’ve been used, and staying away from other people if you’re unwell.
“It’s also essential that vulnerable patients such as elderly patients, those with underlying health conditions, and young children come forward to receive their flu vaccinations and Covid-19 boosters when they are invited for them,” said Hawthorne. “Getting vaccinated is the best possible protection that we have against these winter viruses, and it is not too late.”