The B.1.617.2 coronavirus variant originally discovered in India last December has now become one the most — if not the most — worrisome strain of the coronavirus circulating globally. Recent research suggests it may the most transmissible variant yet and has fueled numerous waves of the pandemic around the world. B.1.617.2 has already spread to more than 60 countries, including the U.S., and undoubtedly contributed to the massive wave of cases that has inundated India in recent months. It also appears to have become the dominant strain infecting unvaccinated people in the U.K., and may be more likely to infect people who are only partially vaccinated than other strains. Below is what we know about B.1.617.2 — also known as the Delta variant.
How is B.1.617.2 different from other variants, and why may it be more dangerous?
The Delta variant has multiple mutations that appear to give it an advantage over other strains. The most important apparent advantage is that the mutations may make the strain more transmissible, which would also make it the most dangerous variant yet. One study indicated B.1.617.2 may be up to 50 percent more transmissible than the B.1.1.7 (U.K./Alpha) variant, and B.1.1.7 is more transmissible than the original strain of the coronavirus, which emerged in China in late 2019.
The bottom line is that if this preliminary research is accurate, the Delta variant may soon become the most dominant COVID strain in the world and lead to rapid outbreaks in countries without high vaccination rates.
There are, so far, no indications that the Delta variant causes more severe illness than other variants, but again, more research is needed.
This chart, created by cardiologist Eric Topol, provides a simple breakdown of how B.1.617.2 compares to other variants of concern:
Why is the B.1.617.2 variant now being called ‘Delta’?
On May 31, the World Health Organization announced that it would give new designations to COVID variants of concern using the Greek alphabet, both because of confusion over the “alphabet soup” names currently in wide use and to prevent variants from being referred to based on where they were first discovered (i.e., the U.K., South Africa, or India variants), a practice that runs the risk of creating harmful stigmas about specific countries and that may become confusing if more than one variant of concern originates in a single country. The WHO has designated the B.1.617.2 variant as Delta.
Scientists will continue to use the more complicated alphanumeric names for variants, as they always have, but the WHO hopes that the Greek-letter-based names will become the widely used ones among nonscientists.
Vaccines appear to be slightly less effective
Recent research by the U.K. government has found that full vaccination is still largely effective against the Delta strain but may slightly be less effective than against other variants, and even less so after only one dose. The research found that two doses of a COVID vaccine provided 81 percent protection against the B.1.617.2 variant (compared with 87 percent protection against the B.1.1.7 variant). One dose only provided 33 percent protection against symptomatic infection from B.1.617.2 (compared with 51 percent protection against B.1.1.7). That means, according to a Financial Times analysis, that a single dose is 35 percent less effective against B.1.617.2 than it is against B.1.1.7.
If that is accurate, it means that B.1.617.2 may be the variant that currently poses the biggest threat to partially vaccinated populations worldwide.
Again, as with every known variant, full vaccination works against the Delta strain — but there are still signs that the variant marks a worrisome evolution in the coronavirus, and it seems likely it could raise the stakes for countries that continue to struggle to vaccinate their populations.
The strain has already become dominant in the U.K. and may threaten the end of its lockdown
As of last week, B.1.617.2 accounted for up to 75 percent of all new cases in the U.K., indicating it is outcompeting the B.1.1.7 (U.K.) strain — now also known as the Alpha strain — and has become the dominant variant in the country.
The rapid spread of B.1.617.2 is prompting warnings that a third wave may already be under way in the country among those who remain unvaccinated. The rise of the variant has led the U.K. to attempt to speed up its vaccination campaign, particularly the second doses that half of U.K. adults still have not received.
Data released on May 27 indicated that nearly 7,000 cases of the B.1.617.2 variant have been confirmed in the U.K., more than double the number that had been confirmed the previous week. U.K. public-health officials have also acknowledged that the increase in cases may be linked to increased testing.
Prime Minister Boris Johnson has already said that the country “may need to wait” to lift its lockdown as planned on June 21, though he has maintained there is not enough evidence to support that move just yet. Some scientists are warning that such a delay must remain an option, informed by evidence rather than a predesignated date.
The good news is twofold. First, because about 44 percent of the U.K. population is fully vaccinated, the number of people the B.1.617.2 strain is infecting remains small and the country is not seeing a surge in hospital admissions. Second, because the U.K. is a world leader in the genome sequencing of variants, it is providing the clearest picture yet of B.1.617.2 capabilities — to the benefit of scientists worldwide.
Why is a more transmissible variant more dangerous?
In a May 28 op-ed for the New York Times, Zeynep Tufekci succinctly broke down the threat of increased transmissibility:
A variant with higher transmissibility is a huge danger to people without immunity either from vaccination or prior infection, even if the variant is no more deadly than previous versions of the virus. Residents of countries like Taiwan or Vietnam that had almost completely kept out the pandemic, and countries like India and Nepal that had fared relatively well until recently, have fairly little immunity, and are largely unvaccinated. A more transmissible variant can burn through such an immunologically naïve population very fast.
Increased transmissibility is an exponential threat. If a virus that could previously infect three people on average can now infect four, it looks like a small increase. Yet if you start with just two infected people in both scenarios, just 10 iterations later, the former will have caused about 40,000 cases while the latter will be more than 524,000, a nearly 13-fold difference.
This is why allowing the coronavirus to spread and evolve unchecked is so dangerous
B.1.617.2 is yet more proof of both how SARS-CoV-2 continues to evolve and how that evolution is continuing to produce variants that are more dangerous than those that came before them. From the available evidence, B.1.617.2 may be the most transmissible variant to yet spread in the world, and thus poses the biggest risk to unvaccinated populations, and possibly also populations where most vaccine recipients have only received one dose. Scientists have good reasons to sound the alarm over it.
And the threat of any more dangerous COVID variant also raises the threat of more dangerous COVID variants which may evolve from it. Vietnam’s health ministry has announced that it has detected a variant which appears to be a hybrid of both B.1.1.7 and B.1.617.2 variants. The country has only been able to give at least one dose of a COVID vaccine to about 1 percent of its population thus far, leaving it highly vulnerable to the new variants despite faring much better than most of the world at preventing the spread of COVID-19. Now Vietnam is racing to do more testing to see how far the hybrid strain has spread and how it differs from its predecessors. (It should be noted that some scientists are urging restraint before jumping to any conclusions about how bad this — or any — new variant is.)
The best way to prevent new variants from evolving is to give the coronavirus fewer opportunities to evolve by preventing and containing outbreaks with effective precautions like face masks and proper ventilation, and by vaccinating people before they can be exposed to infection in the first place.