The highly contagious Delta variant has become the dominant coronavirus strain in the US, accounting for more than 51 per cent of Covid infections in the country, according to new data released by the Centres for Disease Control and Prevention.

The variant, also known as B.1.617.2, was first detected in India in December and is spreading quickly across the globe. In some parts of America, the delta strain accounts for more than 80 per cent of new infections, including some Midwestern states like Missouri, Kansas and Iowa.

It is already causing 74.3 per cent of infections in Western states, including Utah and Colorado, and 58.8 per cent of infections in Southern states like Texas, Louisiana, Arkansas and Oklahoma, according to CDC estimates.

New Covid infections with the Delta variant now account for 51.7 per cent of the infections. The B.1.1.7 or Alpha variant makes up for 28.7 per cent cases after remaining a dominant variant for months, the data said.

"If ever there was a reason to get vaccinated, this is it," Dr. Anthony Fauci told CNN on Tuesday.

The variant poses a "significant threat," to unvaccinated people, said the director of the National Institute of Allergy and Infectious Diseases.

He said the variant was not only more transmissible, but it can also cause more severe disease.

Experts believe it is expected to be the most dominant strain in the country in the coming weeks.

According to the Galveston County Health District in Texas, more than 450 adults and youth in grades 6 to 12 from the area attended a camp in Galveston County and the health District has confirmed 57 cases.

Of the 57 cases reported to date, six are breakthrough cases, the health officials said. Breakthrough cases are defined as someone becoming infected more than 14 days after their second COVID-19 vaccination.

Knowing that there are only six people that got COVID after getting vaccinated, I think still is a very small percentage, said Annamarie Davidson, MD, with Memorial Hermann Hospital.

The county health district said 47 cases are youth and adults 12 years and older while 10 are younger than 12 years.

In addition to these 57 confirmed cases, more than 90 people including non-Galveston County residents have self-reported to the health district that they have tested positive.

We're testing for the Delta variant to see if that's the cause for it spreading so rapidly among that group. It's a good cautionary tale for other churches considering get-togethers. Be careful, particularly when planning get-togethers for kids most of whom haven't been vaccinated yet, said Dr Philip Keiser.

Throughout the country, the rates are not that great so there are a lot of susceptible children, said Dr Catherine Troisi, an infectious diseases epidemiologist at UTHealth School of Public Health.

According to the CDC, one in five children between 12 and 15 years old are fully vaccinated. In the 16 to 17-year-old age group, approximately one in three have got the shots.

Dr Randall Olsen, who works in the genome sequencing lab at Houston Methodist where every positive COVID-19 test in the health system is analysed, said they had identified 4 delta variant cases in late April.

We're now at in the Houston Methodist system 48 patients infected with the Delta variant, he said.

It's hard to make really strong inferences, but it does seem it's causing more hospitalisations. It's definitely infecting the non-vaccinated population, he said.

Local health officials say there is growing concern about the increasing number of adults and children with the Delta variant.

"This virus has thrown every curve ball at us that we can imagine. It is absolutely here, and there is no reason to behave like it won't behave like the other variants, like it has in other communities," said Dr David Persse, the Chief Medical Officer for the City of Houston.

"This transmits a lot more easily, so every time the virus gets that ability to transmit earlier, the per cent of the population that needs to be immune goes up in order to slow it down through herd immunity," he said.

The Texas Department of State Health Services says 41.9 per cent are fully vaccinated.

"The main risk that typically happens with Covid-19 that causes you to end up in the hospital are respiratory- having trouble breathing. There is a possible risk that that chance is increased with the Delta variant compared to some of the other variants," said Dr Maria Rivera with Harris County Public Health.

Rivera said the recommendations are that any child that is over the age of two that has not been vaccinated must continue to wear a mask when they are in public places.

Dr Peter Hotez, dean of the School of Tropical Medicine at the Baylor College of Medicine in Houston, termed the Delta variant an overwhelming concern .

"Anyone who has not been vaccinated or previously infected and recovered, there's a high chance their luck is about to run out. They're about to get Delta," Hotez said.

Texas A&M University virologist Benjamin Neuman said vaccines authorised for use in the US appear to provide protection against the Delta variant, but a large number of unvaccinated individuals in Texas remain a concern.

According to the Texas Department of State Health Services, less than half of Texans over the age of 12 approximately 48.2 per cent are fully vaccinated.

This low-information position makes it difficult to predict how big of a threat the Delta variant will be.

It really depends on what's out there, and at the moment we're not sure. At best you might be able to get away with it, at worst it could be really bad. I think we just don't know, Neuman said.

Mutation is how the virus responds to the world. It's basically how they are able to stay in the game, how they're able to stay competitive, he said.

In the Delta variant, the mutation is a change in position in its spike protein, which allows the virus to penetrate and infect healthy cells.

Though a strain may have advantages over others, its spread often comes down to the activity of people, Neuman said.

Two people standing 20 feet away from each other probably won't transmit the virus, regardless of the variant. But if an individual is in close contact with someone who's infected, they're likely to be exposed and likely will catch that variant if they don't have immunity.

Our vaccination rates are not high enough to where we can expect that this virus will go away on its own. The more unvaccinated people there are, the more opportunities for the virus to multiply," Neuman said.

PTI