WASHINGTON, June 16 (Xinhua) -- More rapid COVID-19 vaccination rollout across the United States, combined with other precaution measures, are essential to prevent emerging coronavirus variants from causing new outbreaks, a leading expert told Xinhua on Wednesday.
The United States has reached another grim milestone Tuesday with over 600,000 coronavirus deaths and more than 33.4 million confirmed cases.
The country remains the nation worst hit by the pandemic, accounting for nearly 20 percent of the global cases and over 15 percent of the global deaths.
Though progress has been seen in key COVID-19 indicators since peak in January, emerging coronavirus variants, including the Delta variant which was first discovered in India, are posing new threats.
"This variant is very dangerous and highly transmissible, greater than the Alpha variant which is currently the dominant strain in the United States," Zhang Zuofeng, professor of epidemiology and associate dean for research with the School of Public Health at the University of California, Los Angeles, told Xinhua in an interview.
It may be associated with an increased disease severity, such as hospitalization risk, compared to Alpha, he added.
The U.S. Centers for Disease Control and Prevention (CDC) has elevated the Delta variant from "variant of interest" to "variant of concern."
Currently, a total of six variants were classified by the CDC as "variants of concern." The Alpha variant, the dominant strain, has led to 69.5 percent of new COVID-19 infections across the country, according to the latest CDC data.
Zhang said whether the Delta variant would replace the Alpha variant to become the dominant strain in the United States depends on the vaccination rate.
"If the vaccination rollout is not fast enough, the Delta variant may progress to a dominant strain, and may also evolve into even more dangerous mutant," he noted.
People unvaccinated and partially vaccinated are most at risk, as study suggests strong protection from COVID-19 vaccines against variants after two doses, Zhang said.
The Pfizer/BioNTech shot is 96 percent effective against hospitalization of those infected with the delta variant after two doses, according to an analysis announced Monday by health authorities in Britain.
Those results are comparable with the protection offered against the alpha variant, which first emerged in Britain, the data show.
Zhang urged more people to get vaccinated as soon as possible to keep the variant from taking hold. He also stressed the importance of keeping social distance, wearing masks and personal hygiene as vaccines could not offer 100 percent protection.
Research is still underway on how long the protection from COVID-19 vaccines will last, and when a booster is required, Zhang told Xinhua.