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The New Delta Variant

Updated: Jul 14, 2021

Like all viruses, the coronavirus that causes COVID is constantly mutating. Most of these mutations have no effect on the virus. However, occasionally a mutation is beneficial to the virus and a new strain is formed. The Delta variant is one such new strain that has become of increasing interest in the US and around the world. For more on how viruses mutate and a discussion of the different variants that are important, you can read my previous two articles: March 1, 2021 “The COVID Variants” and May 30, 2021 “Renaming the COVID Variants” which can be found by visiting .

The Delta variant, originally named B.1.617.2, was first identified in India in December and lead to the big outbreak they have been having. It is more contagious than the original strain of the virus meaning that once it enters a person’s system it is more likely to cause an infection. In a pristine situation where no one is wearing masks and no one is immune (from vaccination or previous infection), a single person infected with COVID will infect about 2.4 more people during the ten days that they are contagious. With the Delta variant, that number is about 75% more, meaning that it will spread to about 4 more people. This has huge consequences when we are talking about the continued spread of the global pandemic as a whole. Because it is much more effective in being transmitted, the Delta variant has already become the dominant variant in both India and the United Kingdom. It currently makes up 20-25% of new cases in the US and will likely become the dominant variant for new infections very soon.

Masks, social distancing, and handwashing remain equally effective in preventing the spread of all of the new variants, just as they are for the original strain, because the way the virus is spread has not changed.

One important question is, “How effective will the COVID vaccines be against the Delta variant?” The Pfizer and Moderna vaccines appear to be around 88% effective in preventing a person infected with Delta from becoming significantly symptomatic. This is compared to 95% effectiveness against the original strain. So, some loss of effect, but still quite good. The Oxford-AstraZeneca vaccine is about 60% effective in preventing serious symptoms from Delta. The Johnson & Johnson vaccine is somewhere in between. For perspective, the effectiveness of the flu shot we get each year ranges from 30% to 70% in effectiveness depending on the year.

If Delta mutates further, then there may be a need to modify the vaccines accordingly. In that scenario, people who are already vaccinated may need to receive a booster shot of the modified vaccine. There is already a shift in Delta being seen in India, which is being called Delta Plus. Delta Plus has an additional mutation at the site where antibodies attach and thus could make the vaccines less effective requiring modification as mentioned.

Another important question is, “Does Delta cause a more serious illness than the original strain?” It is difficult to tell at this point because the death rate in India from Delta may have been worse simply due to the lack of adequate hospital beds and oxygen as their healthcare system became overwhelmed. The Delta cases in the United Kingdom might be more comparable to what we can expect here in the US. In one study published of cases in Scotland, the rate of people requiring hospitalization was about double with Delta than the original strain which carries a hospitalization rate of about 12% (meaning about 12% of people who get infected with the original strain of COVID in the US so far have required hospitalization).

The California Department of Public Health (CDPH) has undertaken an ambitious strategy to monitor the spread of these different variants. They are attempting to determine the variant type of every new positive case in the state. CDPH announced on July 1 that Delta now comprises 35% of all new cases in California. During the surge of cases in Southern California during last winter, the dominant variant was Epsilon which made up 60% of all cases in the state. Epsilon has now dropped to only 2% of new cases. Epsilon, by comparison, is only 35% more contagious than the original strain versus 75% with Delta as previously mentioned.

Another question that needs to be answered is, “Should we return to mask mandates for vaccinated persons?” Clearly, unvaccinated persons should be particularly careful to wear masks, now more than ever. With the current effectiveness of the vaccines preserved against Delta, perhaps not. However, if the effectiveness of the vaccines begins to drop say with Delta Plus or some other new variant, then perhaps. There is nothing to stop a vaccinated person from choosing to still wear a mask in public. I have been tending to wear my mask in public, probably because old habits die hard.

Delta, therefore, carries serious implications, especially for persons who are unvaccinated. The best strategy would be to get vaccinated as soon as possible if you aren’t already. Hopefully, we won’t see a surge in cases that require shutting down sectors of the economy again. Keep in mind, vaccination not only reduces the risk of serious illness, but dramatically reduces the chance that a vaccinated person who becomes infected will be contagious. Vaccination is clearly an effective strategy, along with mask wearing, social distancing and handwashing, in preventing a return to the restrictions we just got away from.

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