The new corona delta mutant was found to have a shorter incubation period and a 1000-fold increase in viral load.

The delta variant (B.1.617.2 strain) of the new coronavirus, which was confirmed in India at the end of 2020 and designated as 'VOC (Variant of Concern)' by WHO on May 11, 2021 , It is said to be more infectious than conventional viruses. According to a preprint by a research team at the Centers for Disease Control and Prevention in Guangzhou, China, published in the journal Nature, 'Delta mutants have a shorter incubation period than conventional ones, and the amount of virus that replicates in the body is also large. It turned out to increase more than 1000 times. '

How the Delta variant achieves its ultrafast spread
https://www.nature.com/articles/d41586-021-01986-w

A new coronavirus vaccine was developed, and it was thought that the spread of infection could be suppressed by gradually increasing the number of inoculators. However, the infection of the delta mutant strain is spreading instead of the conventional strain, and the number of newly infected strains is increasing steadily.

At a Senate hearing on July 21, 2021, Rochelle Walensky, director of the Centers for Disease Control and Prevention (CDC), said, '83% of new coronavirus infections in the United States are infected with the delta variant. I testify.

Delta variant now makes up 83% of new COVID-19 cases in US | Live Science
https://www.livescience.com/covid-delta-variant-majority-cases-us.html

In the United States, as of July 21, 48.6% of the total population has been vaccinated, but there is a large regional disparity in vaccination rates, and the vaccination rate is less than 40% in two-thirds of the United States. .. According to Warensky, highly infectious delta mutants have been identified in areas with low vaccination coverage and the infection is spreading rapidly. Following the spread of the Delta mutant, the CDC cautions against 'always wearing a mask after vaccination.'

Interim Public Health Recommendations for Fully Vaccinated People | CDC
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/fully-vaccinated-guidance.html

In addition, the Israeli Ministry of Health said, 'Pfizer's new coronavirus vaccine has been shown to be about 90% effective in the past, but it has decreased to about 66% for delta mutant strains.' Announced. Regarding this, Pfizer claims that the vaccine, which was originally given twice, will be 'significantly improved in efficacy against the delta mutant strain by hitting it three times,' and reports that it will apply for approval of the booster vaccination to the U.S. regulator. Has been done.

Pfizer Apply to FDA for Third Vaccine Permit | Newsweek Japan Official Site
https://www.newsweekjapan.jp/stories/world/2021/07/fda3.php

A research team at the Centers for Disease Control and Prevention in Guangdong Province, which announced the preprint, followed up 62 people who were first infected with the Delta mutant in mainland China. During the period of infection, the research team examined the amount of virus in the participants' bodies and how it changed over time. We then compared the pattern with 63 people infected with the original strain of the new coronavirus in 2020.

The virus was first detected in people infected with the Delta mutant on average four days after infection. On average, 6 days later for those infected with the original strain, suggesting that the delta mutant strain may replicate faster. In addition, the viral load of people infected with the delta mutant strain was 1260 times that of people infected with the original type.

'The strength of the infectivity of the Delta variant can be explained by its short incubation period and high viral load,' said Benjamin Cowling, an epidemiologist at the University of Hong Kong. The increase in the number of people means that more people can be infected by the super spreader. '

However, there are still many unclear points about the delta mutant strain, such as how the delta mutant strain is 'easier to become severe' than the original strain and how much it has the ability to evade the immune system. Emma Hotcroft, a genetics researcher at the University of Bern, said, 'I'm just surprised by the new coronavirus. It's a mystery by examining the population infected with delta mutants and other variants in more detail. We can expect that the wrapped part will be revealed as much as possible. '