The Difference Between Delta, Delta Plus, and Lambda

Delta Plus, a variant of a variant, is the latest strain of the COVID-causing coronavirus to make the news. (A previously-known variant, Lambda, is also making headlines.) So far, there’s nothing to panic more about: Delta is scary enough.

What’s the difference between Delta and Delta Plus?

Delta is the more-transmissible strain of the coronavirus that is fast becoming the dominant strain worldwide. It’s as contagious as chickenpox and substantially more contagious than ordinary colds or flu. Because it’s so contagious, measures that were enough to slow the spread of original-strain COVID seem not to be enough to stop Delta. More people need to be vaccinated to beat a more contagious virus, so masks and other safety measures need to be applied more diligently.

Delta Plus is the nickname of a Delta variant with one extra mutation. That mutation was also found in the Alpha variant that was spreading earlier this year, according to the Washington Post. Reuters reported in June that this new mutation might make the virus harder for our immune system to track down and destroy.

We don’t know yet if vaccines are less effective against Delta Plus than they are against Delta. We do know that a single dose of the Pfizer vaccine is less effective against Delta than against the original COVID virus, but that a double dose is still protective.

OK then, what’s Lambda?

Lambda is still categorised by the World Health Organisation as a “variant of interest,” less worrying than the “variants of concern” like Delta.

It seems to be in the news this week because it’s riding on the coattails of the Delta Plus panic, but there’s nothing new or unusually worrying about it. A recent study showed that one Chinese vaccine (Sinovac/CoronaVac) may not protect very well against it, but that same vaccine was already suggested to be less effective against some variants than the vaccines currently available in the U.S.

Why do we keep hearing about new variants?

As long as vaccination rates are still low, the virus has plenty of room to live and grow and reproduce and evolve — every unvaccinated person is a potential home and playground for the virus. (Most vaccinated people are still immune to the virus, for now.)

If we had managed to contain COVID-19 with masks and distancing in early 2020, it may not have had enough time or opportunity to branch out into all these variants. Likewise, if we had managed to get more people vaccinated more quickly — across the world — the virus would have had fewer opportunities to evolve.

But the nature of evolution is that the more successful variants tend to out-compete their less transmissible cousins. Once Alpha got going, it took over and became the dominant variant; now Delta is doing the same thing. And as long as we give the virus plenty of people to reproduce in, and opportunities to travel from person to person, this will keep happening.

Vaccination is still our best bet to build immunity to the virus on the population level, but other measures like masking up and avoiding indoor crowds are important, too. The vaccine is likely to provide more robust, longer-lasting immunity than the kind you get from surviving a bout of COVID yourself, making it especially important to get your shot.