The amazing effectiveness of the coronavirus vaccines, which offer recipients up to a 95 percent chance of escaping serious illness, has changed the course of the pandemic in the U.S.

You may be wondering why a similar vaccine can’t be made for another viral infection—the common cold. Is the facial tissue lobby to blame?

While a common cold vaccine is within the realm of possibility, the reason it hasn’t been developed after decades of trying is simple: With more than 200 types of viruses causing colds, a vaccine targeting them all is a high bar to clear. The rhinovirus, which causes 50 to 75 percent of all colds, has more than a hundred different strains.

As immunologist Peter Barlow put it to Scientific American in 2018, trying to create a single vaccine for such a formidable variety is a huge hurdle. “It’s incredibly difficult to create a vaccine or drug that will target all of those 160 [strains],” he said.

While cold vaccine research began in earnest in the 1950s, it wasn’t until the 1990s that the huge assortment of rhinovirus strains was fingered as the primary culprit for colds, which may have actually discouraged research—the problem seemed too sweeping to tackle.

From a resource standpoint, there’s also a question of how beneficial a vaccine might truly be. While colds are a nuisance, they’re usually self-limiting—that is, most people recover within a week and suffer no lasting effects as a result of infection. (People with lung issues can, however, be slower to recover or suffer complications.) Scientists tend to prioritize vaccines targeting illnesses that can result in serious infection or death, like measles, influenza, polio, and pneumonia.

For a common cold vaccine to work, it would have to target multiple virus strains to provide at least partial coverage against the most common types. This is certainly possible: The pneumonia vaccine can cover 23 different bacterial strains. Alternately, scientists may one day be able to isolate parts of the viral structure common to many colds and develop a vaccine against them.

In the meantime, the best ways to avoid colds are ones we’ve had plenty of experience with over the past year. Washing hands, avoiding people with symptoms, and covering our faces when coughing or sneezing can help reduce the spread.