BI Answers: Why don’t we have a cure for the common cold?
Modern science has eradicated smallpox, extended life expectancy, and made huge gains in battling some of the world’s deadliest diseases. So why can’t we knock out the humble cold?
The short answer is twofold. First, what we think of as a cold is actually caused by many different viruses. Even the most common among those, rhinovirus, has over a hundred different strains. “Curing” a cold would actually mean eradicating a long list of respiratory viruses that happen to cause similar symptoms. Those symptoms, incidentally, are mostly just your immune system kicking into high gear to fight off an infection, something that can manifest as inflammation in the throat and congestion in the nose.
Second, while sniffling and coughing is no fun, a cold is pretty low down on the list of ailments that need curing. It can be a concern for infants, the elderly, or those with pre-existing respiratory conditions, but “for the majority of us, a common cold is more annoyance than threat,” says Ian Mackay, a virologist at the University of Queensland.
Still, in 2002, researchers calculated that the annual cost of lost productivity due to colds is $25 billion. The National Institutes of Health estimates that people in the United States experience about 1 billion colds every year. What if we could make those all go away? We talked to a number of experts to get the full story on why we haven’t cured the common cold — and whether we ever will.
Why isn’t there a cold vaccine?
Every year, there are multiple strains of the flu circulating. If we can vaccinate against the most common strains of the flu, it seems like we should be able to do the same thing for colds. But it doesn’t quite work that way.
There are only about three strains of flu each season, while “there are usually 20-30 different types of rhinovirus circulating each season in one geographic area,” explains Yury A. Bochkov, an associate scientist in the department of pediatrics at the University of Wisconsin School of Medicine and Public Health. Only about 10% of those will show up again the next year. That means, Bochkov says, that public health officials “cannot predict the spectrum of rhinovirus types for an upcoming cold season.”
Plus, even if you could, as Thomas Smith of the University of Texas Medical Branch at Galveston says, “somehow stuff 100 different strains into one shot,” that would only take care of the most common cold-causing virus.
Over 200 viruses can cause what a sick person would recognise only as a cold, including “some strains of influenza virus, adenoviruses, coronaviruses, enteroviruses, [and] respiratory syncytial virus,” Bochkov explains. A rhinovirus vaccine would do nothing to protect against those.
Why isn’t there a cold cure, or even a highly effective treatment?
The main reason, says Mackay, is that the common cold is usually “a short-lived and relatively mild illness.”
But trying to develop drugs to treat rhinovirus also has some particular challenges. Smith, who worked on such research in his lab at the Donald Danforth Plant Science Center, tells us that some of the approaches they were testing “really did work,” at least in the lab. Still, “while these compounds were pretty good at hitting a number of different strains at once, there were still a few outlier strains.”
That’s the tricky thing about rhinoviruses, says Bochkov: “It is difficult to find an antiviral equally efficient against 160 rhinoviruses.”
Furthermore, colds are not usually life-threatening, so the Food and Drug Administration would have a very low threshold for the kind of side effects that would be considered worth it. “It really had to be nearly as safe as water for approval for the general public,” says Smith. Few drugs are.
The challenges did not stop there. “Only humans show symptoms of [rhinovirus] infection,” explains Smith, making it nearly impossible to do any testing between petri dishes and human trials. Even then, researchers would first have to find a rhinovirus that test subjects had not already been exposed to — a difficult task with so many strains circulating every year.
If anyone is able to find an effective treatment, however, those efforts might pay off. “There would be a huge market among wealthy nations who have overcome some of the more serious infectious diseases and now have moved their attention to removing the annoyance of the common cold,” predicts Mackay.
Is there any progress being made?
A number of researchers are working on something called broad-spectrum antivirals, which would target a wide variety of viruses. While much of this research is still in very early phases, it may offer the best hope for an eventual cold cure.
Todd Rider, formerly a senior staff scientist at MIT Lincoln Laboratory and now at Draper Laboratory in Cambridge, developed one such compound, called DRACO. It generated a lot of media buzz when it was first announced in 2011.
DRACO, Rider tells us, “is designed to treat or prevent infections by a broad spectrum of viruses, just as existing antibiotics can treat or prevent infections by a broad spectrum of bacteria.”
The compound has so far been effective against 15 different viruses in cells and in mice. It works by entering all cells and then destroying those where it detects a viral infection. “For the common cold in particular, DRACO was shown in human cells to be effective against all four rhinovirus strains tested,” Rider explains, “and to completely eliminate rhinoviruses without harming uninfected cells.”
While DRACO and other related research, like that led by Leo James at Cambridge University’s Laboratory of Molecular Biology, seem very promising, much more testing is needed to see whether this approach will be effective and safe in humans. If DRACO lives up to its initial promise and continued testing goes well — neither of which is a certainty — Rider expects that it could be used in humans “within a decade or perhaps sooner.”
What can you do in the meantime?
Or, Smith notes, there’s always the extreme option: “Hermits who never see fellow human beings never get the common cold.”
This post is part of a continuing series that answers all of your “why” questions related to science. Have your own question? Email [email protected] with the subject line “Q&A”; tweet your question to @BI_Science; or post to our Facebook page.