For those of us in the Northern Hemisphere, it’s the season of the sniffles. As the weather turns, we’re all spending more time indoors. The kids have been back at school for a couple of months. And cold germs are everywhere.

My youngest started school this year, and along with artwork and seedlings, she has also been bringing home lots of lovely bugs to share with the rest of her family. As she coughed directly into my face for what felt like the hundredth time, I started to wonder if there was anything I could do to stop this endless cycle of winter illnesses. We all got our flu jabs a month ago. Why couldn’t we get a vaccine to protect us against the common cold, too?

Scientists have been working on this for decades. It turns out that creating a cold vaccine is hard. Really hard.

But not impossible. There’s still hope. Let me explain.

Technically, colds are infections that affect your nose and throat, causing symptoms like sneezing, coughing, and generally feeling like garbage. Unlike some other infections,—covid-19, for example—they aren’t defined by the specific virus that causes them.

That’s because there are a lot of viruses that cause colds, including rhinoviruses, adenoviruses, and even seasonal coronaviruses (they don’t all cause covid!). Within those virus families, there are many different variants.

Take rhinoviruses, for example. These viruses are thought to be behind most colds. They’re human viruses—over the course of evolution, they have become perfectly adapted to infecting us, rapidly multiplying in our noses and airways to make us sick. There are around 180 rhinovirus variants, says Gary McLean, a molecular immunologist at Imperial College London in the UK.

Once you factor in the other cold-causing viruses, there are around 280 variants all told. That’s 280 suspects behind the cough that my daughter sprayed into my face. It’s going to be really hard to make a vaccine that will offer protection against all of them.

The second challenge lies in the prevalence of those variants.

Scientists tailor flu and covid vaccines to whatever strain happens to be circulating. Months before flu season starts, the World Health Organization advises countries on which strains their vaccines should protect against. Early recommendations for the Northern Hemisphere can be based on which strains seem to be dominant in the Southern Hemisphere, and vice versa.

That approach wouldn’t work for the common cold, because all those hundreds of variants are circulating all the time, says McLean.

That’s not to say that people haven’t tried to make a cold vaccine. There was a flurry of interest in the 1960s and ’70s, when scientists made valiant efforts to develop vaccines for the common cold. Sadly, they all failed. And we haven’t made much progress since then.

In 2022, a team of researchers reviewed all the research that had been published up to that year. They only identified one clinical trial—and it was conducted back in 1965.

Interest has certainly died down since then, too. Some question whether a cold vaccine is even worth the effort. After all, most colds don’t require much in the way of treatment and don’t last more than a week or two. There are many, many more dangerous viruses out there we could be focusing on.

And while cold viruses do mutate and evolve, no one really expects them to cause the next pandemic, says McLean. They’ve evolved to cause mild disease in humans—something they’ve been doing successfully for a long, long time. Flu viruses—which can cause serious illness, disability, or even death—pose a much bigger risk, so they probably deserve more attention.

But colds are still irritating, disruptive, and potentially harmful. Rhinoviruses are considered to be the leading cause of human infectious disease. They can cause pneumonia in children and older adults. And once you add up doctor visits, medication, and missed work, the economic cost of colds is pretty hefty: a 2003 study put it at $40 billion per year for the US alone.

So it’s reassuring that we needn’t abandon all hope: Some scientists are making progress! McLean and his colleagues are working on ways to prepare the immune systems of people with asthma and lung diseases to potentially protect them from cold viruses. And a team at Emory University has developed a vaccine that appears to protect monkeys from around a third of rhinoviruses.

There’s still a long way to go. Don’t expect a cold vaccine to materialize in the next five years, at least. “We’re not quite there yet,” says Michael Boeckh, an infectious-disease researcher at Fred Hutch Cancer Center in Seattle, Washington. “But will it at some point happen? Possibly.”

At the end of our Zoom call, perhaps after reading the disappointed expression on my sniffling, cold-riddled face (yes, I did end up catching my daughter’s cold), McLean told me he hoped he was “positive enough.” He admitted that he used to be more optimistic about a cold vaccine. But he hasn’t given up hope. He’s even running a trial of a potential new vaccine in people, although he wouldn’t reveal the details.

“It could be done,” he said.

This article first appeared in The Checkup, MIT Technology Review’s weekly biotech newsletter. To receive it in your inbox every Thursday, and read articles like this first, sign up here.