(NEXSTAR) – Measles cases nationwide jumped dramatically this week, according to new numbers reported by the Centers for Disease Control and Prevention on Friday.

Nearly half of states are now reporting cases of the highly contagious virus, which can spread “like a forest fire” through unvaccinated or undervaccinated communities.

At least 483 cases are now confirmed in Alaska, California, Florida, Georgia, Kansas, Kentucky, Maryland, Michigan, Minnesota, New Jersey, New Mexico, New York, Ohio, Pennsylvania, Rhode Island, Tennessee, Texas, Vermont, and Washington, according to the CDC.

At the beginning of the month, the number of confirmed cases was just 164.

Minnesota and Tennessee are the newest states to detect measles, and a new outbreak of at least 10 linked cases was confirmed in Ohio this week.

“Given the measles activity in Texas, New Mexico, and other states around the country, we’re disappointed but not surprised we now have several cases in Ohio and known exposure in some counties,” said Ohio Department of Health Director Dr. Bruce Vanderhoff. “This disease can be very serious, even deadly, but it is almost entirely avoidable by being properly vaccinated.”

Measles is considered one of the most contagious viruses in the world.

“On average, one infected person may infect about 15 other people,” Scott Weaver, a center of excellence director for the Global Virus Network, an international coalition, told the Associated Press. “There’s only a few viruses that even come close to that.”

The MMR (measles, mumps and rubella) vaccine is effective at preventing spread of the virus, but childhood vaccination rates have dropped as more families claim exemptions for religious or personal reasons. The first MMR shot is recommended for children between 12 and 15 months old and the second between 4 and 6 years old.

Measles isn’t usually deadly, but it can have serious complications, especially for young children. Among kids with measles, about 1 in every 20 develops pneumonia, which can be fatal. Rare cases also suffer swelling of the brain called encephalitis — which can lead to convulsions, deafness or intellectual disability.

Fourteen percent of cases this year have required hospitalization, the CDC says. Most of those hospitalized have been children.

The Associated Press contributed to this report.