The Delta variant (B.1.617.2) of SARS-CoV-2, originally discovered in India last December, has ignited a surge in COVID-19 cases across the U.S., as it has quickly become the dominant strain in the U.S., accounting for at least 93 percent of all new sequenced cases in the country. Below is what we know about the Delta variant.
SARS-CoV-2 belongs to the mRNA virus, and it is prone to have gene mutations. From the perspective of the entire virus evolution and ecology, this is also a selective evolution of the virus—it can always choose the way that is beneficial to its own survival and reproduction.
The Delta variant has a total of 15 selective evolutions, of which 3 key mutations of L452R, E484Q, P681R, L452R, and E484Q occur in the region where the spike protein binds to the Angiotensin Converting Enzyme 2 (ACE2) receptor on human cells. L452R mutation improves the ability of the virus to invade cells, E484Q mutation helps to enhance the immune escape of the virus, and P681R mutation can make the virus’ invasion more efficient. All these mutations give the Delta variant 3 new transmission characteristics.
- Higher viral load: In Delta variant cases, PCR detection of samples showed a particularly high nucleic acid load, and the CT (cycle threshold) of the infected person is very low, indicating the viral load is obviously higher than that of the patients infected last year. As a result, the proportion of infected people who are forwarded to severe cases after the onset of illness is high, and the time to become severely ill is shortened.
- Advanced transmission ability: the incubation period of patients infected with COVID-19 in 2020 is 5.9 days on average, and the Delta variant is only 3.2 days on average. The transmission speed of the variable virus is obviously accelerating, which is 40% higher than the alpha variant of SARS-CoV-2.
- Stronger immune escape: Under normal circumstances, after the body is infected with the coronavirus or received SARS-CoV-2 vaccination, the body's immune system will produce specific antibodies. When the new virus enters the body, the antibodies prevent the virus from growing and reproducing in the body. While for the Delta variant, its immune escape means that the killing effect on the virus is weakened, and the protection rate of the population after vaccination is reduced, impeding the development of an immune barrier by vaccines.
However, experts also proved that Pfizer and Moderna vaccines can still protect people from delta variants, but their effectiveness is slightly reduced compared to the original strain. In May of this year, British researchers reported that the Pfizer vaccine is 88% effective against symptomatic diseases from delta variants, and 2 doses show better protection than 1 dose only. In addition, the CDC has resumed guidance on wearing masks indoors, especially in areas with low vaccination rates and high transmission rates. Although the outdoor transmission rate is still relatively low, wearing masks in the population can indeed provide more protection, especially for those who have not been vaccinated.
