News stories are appearing everywhere about new coronavirus variants appearing globally (in 31 countries as of Dec 31, 2020) and in the U.S. (California, Florida, Colorado). While print and online sources generally treat this news with caution, talk of mutant viruses is front and center in the television and radio news cycle. On my short drive to the grocery store yesterday I heard nothing but news coverage of new coronavirus strains, which started to make me anxious even though I am usually pretty resistant to that. I figure if the news is freaking me out, it probably is freaking everyone out even more. In this post, therefore, I will tackle what ‘viral variants’ (or ‘mutants’) actually are, what we know about these new variants, and what this means for our health and safety. I’m going to hit all these topics quickly in this first post, and then write out more science-y follow up in a separate post.
Viral variants are versions of a virus that differ from other versions in one or more places in their genome. These variants are made when errors occur during viral replication – when the genetic material of the original virus is copied to make new viruses. Because each new error (or mutation) that differs from the original copy makes a new ‘variant’, variants are actually quite common. Over 16,000 different versions of the COVID-19 virus were known as of September 2020, most differing from each other in a single nucleotide, and 1,000 variants of SARS-CoV-2 were known to be circulating in different populations as of November, 2020.
Viral populations quickly evolve over time – the versions of the coronavirus we are seeing in December 2020 are not the same as what we were dealing with in March of the same year. Some copy errors result in changes that are damaging for the virus, some have little or no effect, and some improve something about the viral infection process. Copy errors are random, but survival is not: variants that hurt the virus’s ability to infect host cells are quickly lost from the population, while those that help the virus in some way quickly become more and more common in the host population (us).
Should we be worried about any of these thousand or more viral variants?
For most of them, no. Random changes in the genetic code of virus (or any organism for that matter) are much more likely to be damaging than to be helpful. The problem with viruses, however, is that they make so very many copies of themselves. Even if 999 out of 1000 variants are bad, that single ‘good’ variant will quickly become more common in the viral population… and if 16,000 or more variants have shown up in less than a year, chances are good that at least a handful of them are ‘new and improved’ models.
Which variants are the news stories talking about, then? In the last 2-3 months at least three coronavirus variants have appeared that quickly became the dominant version in local populations, including one in the U.K., one in South Africa, and one in Nigeria. While a number of factors can affect the abundance of different variants in a population, this very quick rise to dominance is a huge warning sign that these three variants may have a ‘selective advantage’; in other words, these variants are ‘better’ than the others at infecting the host. But ‘better’ how? Any change that improves how well a virus attaches to host cells, how well it reproduces inside the host, how good it is at dispersing from one host to another, or how long it can persist in the environment could lead to a variant becoming more common.
What does the appearance of these three viral variants mean for us? In order to think this through, we need to consider two different ways that a virus could be ‘worse’ – it could be more infectious, or it could be more pathogenic (or both). If a virus becomes more infectious, each infected person will in turn infect more people than previously (the viral R-value will increase). If a virus is more pathogenic, more of the people who become infected will develop severe disease. Viruses that are more infectious are not necessarily more pathogenic. For example, the virus that causes mononucleosis (EBV) is extremely infectious: 90% of the U.S. population carries a persistent EBV infection, with 50% of us infected before we turned 5 years old. However, mononucleosis is not a very common disease: only 0.5% of the population is diagnosed with ‘mononucleosis’ each year.
Are these new coronavirus variants more infectious? Are they more pathogenic?
Data support that at least two of the three variants being tracked are more infectious. The variants are more transmissible (jump from person to person more easily), but exactly how this improved transmission happens is not known. All three variants first appeared just in the last two or so months, so we don’t have a concrete answer to this, but researchers in the U.K. estimate that the UK variant has an R-value 0.7 higher than the previous variants. To put it in different terms, the virus may be between 50%-70% more transmissible than the earlier version.
As we already know, viruses do not stay put. As people move from place to place around the globe, they bring their infections with them. The U.K. variant has already been found in California, Colorado and Florida. Because of the variant’s increased transmission rates, we can expect to see it become more common in those states and in others. As it increases in prevalence, infection rates will increase even if those states have social distancing measures in place. And we will see a similar increase in infection rates across the globe as this and other more transmissible variants (for example, the one from South Africa) continue to spread.
What does that mean for us? The rate of spread of this virus is going to increase, and, even though we are tired and frustrated with social distancing measures, we are going to have to be even more vigilant than before. An R-value has to be below 1.0, or fewer than one new infection for each currently infected person, for a pathogen to start declining in a population (for the curve to start trending down). While the initial R-value estimates for SARS-CoV-2 were between 2-3, the UK’s current social distancing rules have brought their R-value down to between 1.1 and 1.3…. until now. Given the new variant’s R-value is 0.7 higher than the previous version, infection numbers in the U.K. will begin to rise more quickly as the new variant becomes dominant, even with the current social distancing rules in place.
Right, that was the bad news… is there any good news?
Yes! while the new variants are more infectious, they do not appear to be more pathogenic. While the variants may increase viral load (infected people make more virus), and have more virus present in their noses and upper respiratory tracts, as of now there is no evidence that any of the variants cause more severe disease. People will get sick (more than we had originally predicted), but at least they won’t be sicker than what we’ve already seen.
Of course the other very good news is the development and approval of two different vaccines for this virus, and likely more on the horizon. But will those vaccines protect against these or other future variants of this virus? The key to answering that question lies in the coronavirus spike proteins, which are the main target for vaccine development. Worryingly, all the three variants in the news (UK, South Africa, Nigeria) have changes in their spike proteins. Are the spike proteins of the new, more infectious, variants similar enough to the original versions that our vaccines will still work? The companies producing the vaccines (Moderna and BioNTech) are looking into this now. Generally speaking, chances are good that our current vaccines will work just as well or nearly as well against these newer variants BUT even if they are less effective, the particular type of vaccine currently in use (mRNA vaccine) is much easier to change and modify than previous vaccines. For more reading on this, please read this Newsweek article, published on Dec 30, 2020.
What is the overall takeaway message?
Viruses evolve over time, becoming ‘better’ at infecting their hosts. These improved abilities usually lead to an increase in how infectious the virus is, but do not necessarily lead to a more severe disease. The virus that causes COVID-19 is evolving, as any virus would, and we are seeing evidence that its transmissibility is increasing, that it is becoming more infectious. However, we have not seen evidence that the newer versions of the virus cause more severe disease, though these variants are quite new and we must continue to watch the data on this. The vaccines currently approved for use should also be effective against these new variants, and likely will also be effective against future variants as well. If these vaccines are not as effective against future variants, the vaccines are fairly easy to modify to improve their efficacy.
Bottom line? The emergence of these viral variants is not unexpected but is worrisome nonetheless. Because of their increased transmission rate, we must be even more vigilant with our social distancing, mask wearing and hand washing, even if all of us are emotionally ‘over’ this whole thing. We must support all vaccination efforts in any way we can – getting ourselves or our family members vaccinated when it’s our turn and supporting the efforts of local and state health officials in any way we can. The only way we’ll get back to what our social lives used to be is to maintain and even intensify our efforts now, on the home stretch. We can do it!
Science in Translation 