Can You Have Another Cold When You’re Already Suffering From One?

Yes, you can have more than one cold at the same time. Doctors call this a co-infection: two different cold-causing viruses (usually two different rhinovirus types) hitting you at once. Your immune system can usually handle both, but the real danger is when a viral cold is combined with a separate bacterial infection.

You know the signs:  your throat is sore, your eyes are watering, your muscles are aching, and your nose won’t stop running. You’ve managed to catch a cold somewhere, and your plans for the weekend are ruined. You can’t imagine how things could get any worse – unless you were to catch another cold at the same time!

As awful as that prospect sounds, is it even possible?

The Many Faces Of A Rhinovirus

The short answer to this important question is Yes, you can definitely have more than one cold at the same time, but that isn’t where the story ends.

Rhinoviruses are the most common culprit behind the common cold, but they aren’t the only one. According to the CDC, more than 200 different viruses can cause a cold, including coronaviruses, parainfluenza viruses, adenoviruses, respiratory syncytial virus (RSV) and human metapneumovirus. Within rhinovirus alone, there are over 150 known types divided into three species (HRV-A, HRV-B and HRV-C), and that catalogue keeps growing. These viruses cause those well-known symptoms and typically take a few days to a week to work out of your system, provided your immune system is up to the task.

Speaking of the immune system, when it spots a cold virus in your nose and throat, it doesn’t lead with T-cells and B-cells. The first wave is your innate immune system: the epithelial cells lining your airways detect viral RNA through receptors like RIG-I and TLR3, pump out type I and type III interferons, and call in inflammatory cells to handle the intruder. Only after the first few days does your adaptive immune system spin up T-cell and B-cell responses that produce neutralizing antibodies specific to that particular rhinovirus type.

However, you can be infected by two different types of rhinovirus at the same time, usually after exposure to two different sick people with two different cold strains. At this point, the immune system has to fight two infections at once, but it isn’t all bad news. The interferons released against the first virus can interfere with the second one (a phenomenon known as viral interference or superinfection exclusion), so the two infections often compete at the cellular level rather than simply doubling the misery. The cold may take a bit longer to clear than a single-virus version, but it isn’t significantly more dangerous on its own. Same-strain reinfection within a few weeks is rare, because your fresh, type-specific antibodies generally protect you against that exact rhinovirus serotype for at least a year (sometimes longer), which is why back-to-back colds are almost always caused by a different virus.

The Dangers Of A Superinfection

In medicine, two simultaneous infections are technically a co-infection, not a superinfection. (Superinfection means a second infection that sets in after a first one is already established, often a different agent that takes advantage of weakened defenses or antibiotic-disrupted flora.) Rhinovirus recombination between two co-infecting strains has been documented, but it is relatively rare and usually happens in a non-antigenic stretch of the viral genome, so it isn’t something that routinely produces a scary new variant inside your nose during a bad week.

Co-infection becomes more uncomfortable when you pick up a rhinovirus and an entirely different respiratory virus at the same time, such as influenza, RSV or adenovirus. Each pathogen calls for a slightly different immune response, so your body has to keep two campaigns running in the same neighborhood (your respiratory tract) at once. You can feel rougher for longer, but for an otherwise healthy person it is rarely dangerous on its own.

When two viruses are contracted by the same host, it may be a longer road to recovery, but it is rarely fatal. However, when the body contracts two different types of infections (a bacterial one layered on top of a viral one, for example) at the same time, the outcome can be much more serious. The immune response for viral and bacterial infections is drastically different, so if the immune system’s resources are split, one infection can run away from it. The classic example is influenza: a substantial share of fatal flu cases involves secondary bacterial pneumonia, most often caused by Streptococcus pneumoniae or Staphylococcus aureus, riding in on a respiratory tract weakened by the virus. The 1918 pandemic was driven heavily by such bacterial co-infections, and even in modern seasonal flu deaths, secondary bacterial infection in the lungs or respiratory system is a major cause.

That being said, if you’re suffering from a fungal infection on your skin and a viral infection in your lungs, the two infections are easier to treat autonomously, as the requirements and locations of the infection are quite different. In other words, if you’re suffering from Athlete’s Foot and start to get the sniffles, there’s no reason to rush to the hospital – your body can handle it…. probably.

However, next time you think you’re “out of the woods” following a nasty cold and suddenly relapse with slightly different symptoms, don’t be too surprised. You’re probably just dealing with two colds at the same time. Restock your tissue box and get comfortable… your immune system is going back to work!