Just a cold or full blown flu? Our expert guide to winter germs

The world is cloaked in a swirling tide of microscopic pathogens. Every year, while we in the northern hemisphere enjoy the summer, health forecasters look to the wintry south of the globe for patterns in this fog of viruses. By analysing this data, the experts can track which bugs are heading our way for cold and flu season and adjust the flu vaccine accordingly.

Despite this work, most of us will still not avoid the sniffles in any given year as, according to the National Institute for Health and Care Excellence (Nice), the average adult catches two to three colds annually, while children catch five to eight. The frequency of these infections is much more prevalent in winter months.

While there is no cure, there are measures you can take to reduce your chances of catching a chill and to hasten recovery when you do succumb.

What is a common cold?

The term common cold has been used for centuries to describe a range of symptoms that were once commonly assumed to be caused by cold weather. These include a blocked and runny nose, sneezing, a sore throat and coughing.

As science has developed, so has our understanding, and it has been known for many years now that there is no single illness that causes this annual health phenomenon. Adrian Martineau, a professor of respiratory infection and immunity at the Institute of Population Health Sciences in the School of Medicine and Dentistry at Queen Mary University of London, says: “The common cold is a constellation of symptoms caused by multiple viruses and occasionally bacteria. It is hard to prevent and treat because it is caused by such a diversity of pathogens.”

The most common of these pathogens is the human rhinovirus, which peaks in late autumn and early spring. Other cold-causing viruses include seasonal coronaviruses, metapneumovirus, bocavirus and respiratory syncytial virus, or RSV. The influenza virus also causes cold-like symptoms.

How do you catch a cold?

There are two ways colds and flu viruses are spread. One is by inhaling airborne virus-containing droplets that are coughed, breathed, or sneezed out by an infected person, and the other is by touching infectious particles and transferring them to your mouth, nose or eyes by touching your face. This latter route of transmission informed much of the public health material about handwashing during the early days of the Covid-19 pandemic, before it was recognised that the main transmission route was via respiration of infected droplets, rather than from infected surfaces.

Who is most at risk of catching a cold?

Exposure to others who are infectious is the main risk factor for catching a cold. Anyone in an environment where there is a lot of transmission, particularly households with early-school children, is at risk.

If you have recently recovered from a cold, you will have a degree of immunity, but only against the virus that you had, so it is possible to recover from one cold virus and catch a different one a few weeks later.

As Martineau explains: “You don’t get cross-protection. Immunity to one doesn’t confer immunity to any others.”

Generally, most cold symptoms are mild, but some people risk developing more severe symptoms. Martineau continues: “Broadly there are risks associated with extremes of age. Smoking is a big risk factor and there is emerging evidence that vaping may be a risk factor too.”

Risk of infection is higher with viruses where asymptomatic carriers are infectious because people are generally unaware that they are infected when they have no symptoms and so continue to mix with others, thereby spreading the virus. This was the case with SARS-CoV-2, the virus that causes Covid-19. Carriers were infectious for around 48 hours before their symptoms started.

Why are some colds worse than others?

Several factors influence the severity of the symptoms. These include the strength of your immune response and the type of pathogen that you are infected with. Influenza, for example, potentially causes more serious illnesses than rhinovirus.

The amount of the virus that you are exposed to – the viral load – might also determine the severity of the symptoms. If you are in close contact with an infected person over a long period, you may get a larger amount of the virus, which could cause a more severe illness. Conversely, brief contact in a train carriage with someone who is infectious may result in a milder case of the illness.

Generally, in the case of colds, it does not matter which pathogen you are infected with, as people with normal immune responses are likely to recover. However, colds can be more problematic for those with asthma or chronic obstructive pulmonary disease, as they can trigger attacks and be quite debilitating.

Viruses are continually evolving and the severity of the symptoms that they cause changes too.

Martineau says: “There is evidence that in the 19^th century there was an outbreak of something that wasn’t too dissimilar to Covid-19 which subsequently mutated to a milder seasonal virus. That’s probably the direction of travel for Covid-19. A lot of the cold symptoms this year will be caused by the Omicron variant of the SARS-CoV-2 virus.”

What are the symptoms of a common cold?

The most common cold symptoms, according to the NHS, are a blocked or runny nose, a sore throat, headaches, muscle aches, coughs, sneezing, a raised temperature, pressure in the ears and face and loss of taste or smell. Generally, all cold-causing pathogens present similar symptoms but occasionally pathogens may cause more specific ones. 

Why are colds more common in the winter?

Chillier weather doesn’t cause colds, but colds are more prevalent in the winter largely because people are indoors more and in close contact in enclosed spaces, which gives viruses more chances to spread. However, there are other theories as to why colds are seasonal. One study published in the Journal of Allergy and Clinical Immunology found that a previously unidentified immune response that helps ward off viruses is inhibited by cold weather, making infections more likely.

Some scientists also theorise that a reduction in vitamin D, which is created in the body by exposure to sunlight, increases susceptibility to cold virus infections. While there is limited data to back this up, the theory has not been conclusively proved.

What is the flu and what causes it?

Flu, or seasonal flu, is a cold-like illness caused by the influenza family of viruses. There are four types of influenza viruses: A, B, C and D. Influenza A and B are the strains that cause seasonal epidemics. C virus is detected less frequently and usually causes mild infections, and D viruses primarily affect cattle and are not known to infect or cause illness in people. There are around a billion cases of seasonal influenza annually, including three to five million cases of severe illness. The flu virus causes 290,000 to 650,000 respiratory deaths annually.

The World Health Organization (WHO) carries out studies into which strains will be prevalent every winter, allowing for a new flu vaccine to be created each year. 

According to data from the UK Health Security Agency, influenza-related mortality for last winter is estimated at nearly 15,000, which is higher than in the previous four years. The data also shows that the season started relatively early in the winter but peaked quickly. Hospitalisations across all ages were higher than average, although some of this may be attributed to increased testing by the NHS compared to previous winters. It is believed that one of the main reasons for the above average number of deaths and hospitalisations will have been the dominant circulating strain, which was influenza A(H3N2), which is known to be more severe in older age groups.

What are the symptoms of the flu?

Flu symptoms come on quickly and can include a sudden high temperature and fever, aches, exhaustion, dry cough, sore throat, headache, difficulty sleeping, loss of appetite, diarrhoea or stomach pain, nausea and vomiting. The symptoms are similar for children but they can also get pain in their ears and seem less active. A flu cough can be severe and last up to two weeks.

Who is most at risk of developing the flu?

Anyone can catch the flu and while it can be particularly unpleasant, most adults will recover in around a week. However, some people are more at risk of severe symptoms. Those at a higher risk are typically 65 years and older or have a chronic medical condition such as asthma, diabetes or heart disease. Pregnant women and children younger than five, especially those younger than two, are also deemed more at risk of developing complications.

Flu can also lead to more serious conditions. “Spanish flu was the last major flu pandemic to have an impact and the reason most people died from that was due to a secondary bacterial infection, staphylococcal pneumonia,” says Martineau. 

“Flu can also induce a severe inflammatory reaction, known as a cytokine storm, which can cause damage. This happened in many of the severe Covid-19 cases and was why one of the treatments that had significant results was steroids that dampen down inflammation. It was the body’s response to the virus that caused the problem, rather than the virus itself.”

What is the difference between a cold and the flu?

Flu is typically more severe and develops quickly. If you feel unwell and then slowly get sicker over a number of days, you are more likely to have a cold. Symptoms of the flu usually come on quite suddenly and make you very ill in a short period of time. Sometimes flu can present as a mild illness that is indistinguishable from the common cold. Recent research has also revealed that people may experience “long colds”, in the form of persistent coughing, stomach pain and diarrhoea.

What makes you more susceptible to colds and flu? 

Dr Gary McLean, emeritus professor in biosciences at the School of Human Sciences at London Metropolitan University, explains that anything that reduces your immune system’s effectiveness can make you more prone to colds and flu.

“Stress, tiredness, poor diet and lack of sleep are some common factors that can suppress immunity and limit your ability to fight off infections, particularly in the early stages. But people still need to be exposed to a virus to get infected, so ultimately what makes people susceptible is putting themselves in positions where the viruses can reach them.”

How can you treat colds and flu at home?

The general advice for both cold and flu infections is to rest, sleep, keep warm, take paracetamol or ibuprofen to lower your temperature and treat aches and pains, and drink plenty of fluids to avoid dehydration. Some products, such as Vicks First Defence nasal spray, may help minimise the risk of a full-blown infection. The manufacturer says it works by trapping viruses in the back of the nose and inactivating them before they develop further along the respiratory tract into a full-blown cold. A 2022 study conducted in vitro found that another nasal spray for trapping allergens and pathogens, Bentrio, was effective at slowing Sars-CoV-2 replication on nasal tissue.

Martineau says: “There are antiviral treatments for Covid-19 and RSV but these tend to be used for people at high risk of severe complications, such as those with profound immunosuppression. The advice for those with common colds and flu is symptom management. It is also important to not give it to other people. Work from home. You are doing your colleagues a favour by staying at home and not passing it on.”

When should I go to the doctor?

Generally, colds do not require a doctor’s appointment. The NHS advises parents with babies or young children who have the flu to request an urgent GP appointment or call NHS 111 if they are worried about the symptoms. Those aged 65 or over, pregnant women and those with a long-term medical condition such as diabetes or a condition that affects the heart, lungs, kidneys, brain or nerves should also see a doctor if symptoms do not improve after seven days, as should those with a weakened immune system, for example, because of chemotherapy or HIV.

Call 999 or go to A&E if you get sudden chest pain, have difficulty breathing or start coughing up a lot of blood.

Martineau adds: “You should contact a doctor if you are getting severely short of breath or feeling extremely unwell.”

How can I prevent a cold or the flu?

McLean advises minimising contact with lots of people, spending more time outside and washing hands.

“In addition, get plenty of sleep, maintain a good diet, try not to get run down and take supplements that can stimulate the immune system,” he adds. “Try to avoid touching common surfaces and then touching your face without washing your hands. 

“Being indoors with a mixture of people and in close proximity for extended periods of time increases your chances of infection. Public transport, crowded indoor areas, mixing with lots of people, not washing your hands, all of these will increase the likelihood of exposure if someone infected is present.”

He also advises keeping vaccines up to date for Covid-19 and influenza.

There are no vaccines for the common cold, and as there are so many different viruses that cause it, people don’t get immunity in the same way that they get immunity to chickenpox or tetanus.

“The viruses are numerous and constantly mutating, and immunity is relatively short-lived in comparison to something like chickenpox,” explains Martineau.

The one exception to this rule is RSV, for which a vaccine has been trialled. Although it has not yet been approved by Nice, the Joint Committee on Vaccination and Immunisation (JCVI), which advises UK health departments on immunisation, recently issued a recommendation that the Government considers programmes of vaccinations against RSV for infants and people over 75.

Many of the public health recommendations that were introduced to reduce the spread of Covid-19 are also effective in reducing the risks of catching and spreading cold and flu viruses. For example, another simple preventative measure is a face mask.

Martineau explains: “Face masks have potential benefits both for the wearer and those in contact with the infected person. In terms of transmission, there is decent evidence that if you have an infection and wear a mask, you reduce the risk of transmitting that virus to other people. That’s true even if the mask isn’t a high-protection mask.

“In terms of masks affording protection to the wearer, that is a higher bar. If you wear a tight-fitting face mask with FFP2 to 3 protection level – with a filter – it can afford some protection but in practical terms you have to be consistent. If you are in a house with someone else, you can protect yourself by wearing a mask while you are out, but your partner is likely to bring the virus home and infect you when you are in and not wearing the mask.”

Finally, ventilation is another simple, effective preventative measure. “Air movement and recirculation should move virus away effectively,” says McLean, although he concedes that in the winter months leaving the windows open to bring in fresh air is more challenging.