Researchers found that among 24 reported cases, Delta was seven-fold more likely to lead to vaccination breakthrough infections than non-Delta lineages.
At the current rate, one in four people contracting the virus now had received vaccine doses
High COVID-19 rate in 0-19 age group in India; frequent post-vax infections with Delta variant: Study
According to the WHO update, the study found an increased number of infections among the 0-19 age group and women, higher mortality and more frequent incidences of post-vaccination infections.
CDC said boosters should be offered to people 65 and older, nursing home residents and those ages 50 to 64 who have risky underlying health problems.
The delta variant has been identified in at least 180 countries, according to the World Health Organization.
There is a small but steady increase in AY.1 since June 2021, which is being monitored, the INSACOG noted.
The ruling represents a drastically scaled back version of the Biden administration's sweeping plan to give third doses to nearly all American adults to shore up their protection.
Delta's ability to spread more easily makes it more of a risk to children and underscores the need for masks in schools and vaccinations for those who are old enough.
The increasingly lethal turn has filled hospitals, complicated the start of the school year, delayed the return to offices and demoralized health care workers.
The researchers studied the convergent antibodies' ability to bind to several variants and found that they no longer bound to some.
One is the surge in the number of new infections and its recoveries. The second is the faster vaccination coverage surpassing the national average during the period.
The country is enduring a record rise in infections, fuelled by the Delta variant, with the health department reporting a nursing shortfall of more than 100,000.
The twin votes represented a heavy blow to the Biden administration's sweeping effort, announced a month ago, to shore up nearly all Americans' protection amid the spread of Delta variant.
The port city of Xiamen has confirmed 33 cases in the past two days. Another 59 cases have been found in Putian, about 150 kilometers (90 miles) north on the coast.
Under the autumn-winter proposals, the government is set to repeal some powers of its emergency Coronavirus Act, brought in to tackle the pandemic last year.