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Everything You Need to Know About the Delta Variant

What it is, why the WHO recommends masks for vaccinated people because of it, and what it means for vaccine protection.

What is the Delta variant?

The Delta variant is one of several versions of the virus that causes COVID-19. It was first identified in India. The Delta variant spreads more easily than other versions of the virus.

Is it more deadly?

This is still a bit unclear. There is some concern that it might cause more severe disease because it causes more virus to build up inside an infected person, leading to easier transmission and more serious symptoms. It’s still very new, though, so what we can say for sure is that the Delta variant is more easily spread - and that alone makes it more deadly because it causes outbreaks more easily. 


To put it in perspective, when the pandemic first started, the average COVID+ person infected 2.5 other people. For the Delta variant, that number rises to between 5 and 8 people. That means it’s at least 2x as infectious, leading to exponentially more infections because those 5 to 8 people will go infect 5 to 8 more, and so on! 


Do vaccines protect against the Delta variant?

Yes, but not perfectly. The two mRNA vaccines, Pfizer and Moderna, are shown to be 90% effective in protecting against the Delta variant. The Johnson & Johnson vaccine is looking like it’s a little less effective against Delta, closer to about 70%. In either case, the reality is that if there are large outbreaks of the Delta variant, people who are fully vaccinated can get infected and spread the virus, even if that’s rare. 


Scientists studied an outbreak of the Delta variant in Israel. About half of the people infected were unvaccinated kids, but of the adults, about half were fully vaccinated with mRNA vaccine (Pfizer). That means that fully vaccinated people can still be infected and likely transmit the virus.


Why is the WHO recommending vaccinated people wear masks? 

Because fully vaccinated people can still get and spread COVID in rare cases, the WHO believes that those who are fully vaccinated should still wear masks - to protect themselves and to stop the spread of the Delta variant. Masks protect you from getting COVID - just wearing a mask reduces your individual risk of getting the virus by 65%. So while the vaccine works really, really well - getting you all the way up to 90% protection - a mask raises that level of protection even more. 


Imagine it this way: if 100 people are fully vaccinated, but come into close contact with someone sick with the Delta variant, about 10 of them might get sick with COVID in what we call “breakthrough cases.” Their symptoms are likely to be pretty mild, or they may have none at all. But they can pass it on to their unvaccinated children, or someone immunocompromised in their family, or to someone at the grocery store who isn’t vaccinated. Like we said earlier, the average person infected with the Delta variant will infect five to eight others. So we might see an outbreak of 50+ people that can be traced back to those 10 breakthrough cases.

Now rewind to those 100 fully vaccinated people. If each of them wore a mask when they came into contact with that person who was sick, only about 4 of them would have been infected. That means our hypothetical outbreak is limited to about 20 people, instead of 50 - less than half the size.



Do we expect the CDC to change its mask guidelines? 

Not necessarily, although it’s certainly possible.

This is still a very, very small subsection of the population - the vast majority of COVID cases in the U.S. are in unvaccinated people, including virtually every single new hospitalization. The WHO is taking an approach aimed at reducing the total number of worldwide cases, and they see wearing a mask as a relatively easy way to curb the spread. The CDC may see it differently - especially considering that mask-use is a highly politicized topic in the U.S. 

If the Delta variant causes severe outbreaks in regions with lower vaccination rates, we might see a change in the CDC recommendation to match the WHO’s more cautious guidance. Los Angeles County was among the first in the U.S. to follow the WHO's lead and recommend that fully vaccinated people continue to wear masks when in indoor public spaces.


Will there be other variants coming?

It’s likely. There have been dozens of variants throughout the past year and a half. We’ve only just started naming them using the Greek alphabet to keep track more easily. While the Delta variant is the most concerning right now, it’s not even the newest. The reality of this global pandemic is that there will continue to be new variants as long as there are new people getting sick with the virus. Most of the world doesn’t even have access to vaccines yet, so we’ll likely continue to see new variants spreading for years. Our best hope is that we can reach a high enough global vaccination rate to curb the spread of the virus, and therefore the evolution of new variants. The good news is that our mRNA vaccines are really excellent tools for the job - in part because they can easily be modified for booster shots if needed. 


So, will we need booster shots for the Delta variant?

Maybe. Right now, the mRNA vaccines show pretty amazing results in terms of protection against the Delta and other variants, though the J&J shot is a bit less effective. Those who received the J&J vaccine might be the first to need a booster dose - and the newest studies show that a booster of mRNA might be the best option. A new study is showing that the mRNA vaccines may provide protection for longer than we had thought, which is good news. It all depends on how quickly the virus spreads and therefore how quickly the Delta variant mutates into something new. At some point, there may be a variant that our mRNA vaccines don’t work as well against, and that’s when we’ll need booster doses that are tweaked to protect against that specific variant. If the vaccines continue to provide good protection against variants, as they do now, then our booster doses will be based on how long it takes until protection starts to wear off - which currently looks like it will be at least a year and possibly even longer.


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Disclaimer: This post is meant for general information and educational purposes only and does not constitute, and is not intended as, any form of medical, legal or regulatory advice or a recommendation or suggestion regarding the same.  No recipient of this information should act or refrain from acting on the basis of this information without first seeking legal advice from counsel in the relevant jurisdiction.