SPRINGFIELD, Mass. (WWLP) – Massachusetts has been reporting new cases of the Delta variant related to COVID-19 for the last couple months.

The Delta variant is COVID’s most serious threat and experts say there are no signs of stopping. The Delta variant of the coronavirus is spreading so quickly in the United States that experts say it’s likely the mutant strain will become predominant in the nation within weeks. More than 150 cases of the Delta variant were identified in Massachusetts between March 13 and May 23, according to the state Department of Public Health.

The variant, first identified in India, is the most contagious yet and could trigger another moderate surge of infections, especially those who are unvaccinated.

“It’s starting to accelerate really quickly in the U.S. So last week, about 10-percent of the virus isolates were the Delta variant. Now it’s up to 19-percent. So it seems to have pretty regular regular doubling,” said Dr. Peter Hotez, Dean of Baylor College of Medicine National School of Tropical Medicine.

Massachusetts hospitals for months have seen COVID-19 hospitalizations drop. New data shows most people who are going to the hospital for COVID-19 are not vaccinated. There have been nearly 4,000 post-vaccine infections in Massachusetts, also known as “break-through” cases.

60 percent of Massachusetts is fully vaccinated compare that to 46 percent nationwide. Experts say the vaccines are highly effective, even for different COVID-19 strains, including the Delta variant. The Delta variant has now been detected in nearly every state.