Many people are reporting the “worst cold ever”. But are colds really much worse this year? And, if so, what is causing it? We asked consultant microbiologist Fidelma Fitzpatrick to explain.

1. Can some colds be much worse than others?

Yes, some colds can be worse than others. This depends on several things, including which virus is causing the cold, the person’s age, how capable their immune system is of fighting the cold, and also if they have existing antibodies against that particular virus.

First, it’s important to know that the common cold is not caused by a single bug. About half of common colds are caused by rhinoviruses, one in ten due to coronaviruses, one in ten to 20 due to flu viruses, and one in 20 due to respiratory syncytial virus (RSV) and parainfluenza viruses. These viruses typically consist of several strains that circulate seasonally, are more common in winter and usually infect the upper respiratory tract.

Common cold symptoms last about seven days—but, in some, they can last up to three weeks. Depending on the virus as well as the age of the person and their immune system, symptoms can vary hugely and include mild symptoms such as a sore throat, headache, fatigue, blocked or runny nose, and sneezing and coughing. But in some people, the symptoms can be much worse. It can spread to the middle ear, sinuses or the lungs (causing pneumonia) or a secondary bacterial infection (more common in people with a weakened immune system, the very young or older people). Common cold viruses can also make certain existing respiratory diseases worse, including asthma and chronic obstructive pulmonary disease (COPD)

2. Have anti-COVID measures, such as mask-wearing and physical distancing, affected our resistance against the common cold?

Anti-COVID “non-pharmaceutical interventions” to reduce the spread of the virus that causes COVID (SARS-CoV-2) include social distancing, avoiding unnecessary crowding, improving indoor ventilation, working from home, school closures, travel restrictions and the use of masks. From early 2020, it was clear that these measures also reduced transmission of other respiratory infections.

If people aren’t exposed to cold viruses as a result of these measures, a lack of immunity can build up and may result in surges of respiratory infection in the coming months and years. This becomes especially important when the non-pharmaceutical interventions are relaxed and people begin to congregate and mix more. Essentially, there is a larger group of more vulnerable people this winter. And a more vulnerable group is at risk of having worse infections.

In addition to common cold viruses, there is also concern that there may be an increase in influenza virus infection this winter, hence the focus on flu vaccine campaigns internationally.

3. So we really are more susceptible to colds?

Evidence suggests that we are. In October 2020, in Hong Kong, large school outbreaks of common cold infections occurred after school attendance resumed. A US study predicted winter 2021–22 RSV peaks and influenza outbreaks outside of the typical season, coinciding with the end of non-pharmaceutical interventions. A surge in RSV infections over summer (not a usual time of year for these infections) coincided with the restrictions easing in Australia. In July 2021, Public Health England issued a warning to caregivers of at-risk children as a result of increasing numbers of respiratory infections in young children.

Hospitals and clinics will need to prepare for future surges of colds and respiratory infections as non-pharmaceutical interventions are relaxed.

4. Conversely, would further mask wearing help against the transmission of colds?

Face coverings or surgical masks when worn correctly (covering the mouth and nose) reduce transmission of respiratory viruses. They act as a barrier, protecting others from the mask wearer’s tiny airborne droplets, as well as partially protecting the wearer from other people’s. This protection is partial as gaps usually exist around the sides of face coverings. Wearing masks in crowded spaces is one measure that could prevent the transmission of colds this winter. Other measures are also important, including hand hygiene.

5. Will SARS-CoV-2 also become just another cold virus?

We don’t know what will happen next with SARS-CoV-2, though the seasonality of the common cold coronaviruses suggests how its transmission could adjust after the pandemic. At the moment, people with SARS-CoV-2 infection can have no symptoms, have common cold-like symptoms, or, for some, severe infection (pneumonia).

We also don’t know how long antibodies stay active against SARS-CoV-2, but evidence from studies of other coronaviruses—such as the ones that cause SARS and MERS—suggest that people are protected for one to two years before protection begins to wane. What is not yet known is what “level” of SARS-CoV-2 antibodies is required for protection (immunity) and if there are tests for other parts of the immune response to the virus that are better at deciding if somebody is protected or not.

Common colds are seasonal and usually more common in winter months. All viruses adapt and mutate to a greater or lesser extent—it’s essential for their survival, and SARS-CoV-2 is no exception. SARS-CoV-2 could potentially adapt to seasonal circulation. In the past, other viruses that have caused pandemics (flu), have replaced previously circulating seasonal strains and thereafter transitioned from a pandemic to a seasonal pattern of infection. What changed after the pandemic was the pattern of appearance (seasonal) as well as levels of immunity in the population. What didn’t change was the variability in symptoms associated with these viruses—these flu strains retained their ability to cause severe infection as well as cause common cold symptoms.

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