I'll be keeping an eye on this one.
Remember that Vietnam borders China, got hit by the virus very early, and despite not being rich, mobilized to get it under control with awesome speed. They recently went 100 consecutive days without community spread. (The few cases they had turned out to be imported.)
To give you a feel for the league they play in, when they had a case show up recently, the contact tracing identified and tested ONE HUNDRED CONTACTS and they all tested negative. That is contact tracing on steroids.
All this is to set context - if Vietnam thinks they have a problem, something really bad may be happening. And you guessed it, Vietnam thinks they have a problem.
They're seeing a new outbreak of community spread. Through their insanely quick and thorough contact tracing, they believe this outbreak is THREE TIMES MORE CONTAGIOUS than the original, and possibly more severe as well. An R of 6 or so puts it halfway between original SARS-CoV-2 and measles, which would make it nearly impossible to contain.
So while this is a very important news item, it's still preliminary. First, estimates of R are very sensitive to a few superspreaders. Vietnam's numbers are still small, so it could be nothing more than bad luck with more big spreaders than usual.
Second, I haven't been able to find any reports on genome sequences to identify the strains. Is this unique to Vietnam? Where did it first show up? Where else is it, and are they seeing similar spread? I'm sure these questions are being studied quickly, but I've found nothing on them yet.
For now, treat this as a cause for concern and something worth watching, while Vietnam and the WHO dive into the details.
https://news.yahoo.com/vietnam-says-strain-coronavirus-behind-095351338.html
https://www.bbc.com/news/world-asia-53549809
https://www.businessinsider.com/vietnam-evacuates-80000-da-nang-small-coronavirus-outbreak-2020-7