Measles has spread to Georgia, Florida, and Tennessee, with more cases reported in California and health officials braced for the virus in Alabama.
The virus is reaching levels not seen in years, with 626 cases recorded in the last four months alone - nearly eclipsing the 667 recorded in all of 2014.
Tennessee officials have contacted 600 people who might have come into contact with a person with measles who traveled across the state earlier this month. Three people have been diagnosed in Georgia, and one in Florida.
The new cases prompted officials in Alabama - neighboring Tennessee and Georgia - to hold a press conference on Monday, calling on citizens to get vaccinated.
The resurgence of the virus, which was all but eliminated in 2000, follows a years-long rise in the number of Americans shunning the vaccine, which is the only treatment against measles.
'It's really been a very sophisticated and widespread campaign of misinformation,' Dr Jeanne Mazzarro, division director of infectious disease at the University of Alabama at Birmingham, told DailyMail.com.
Dr Jeanne Mazzarro director of infectious disease at the University of Alabama Birmingham, told Daily Mail the campaigns against vaccines have taken on a life of their own
Measles is an infectious disease, which starts as a fever and a rash. It can develop into inflammation inside the body and brain, and it hampers the immune system, making sufferers more susceptible to pneumonia.
But there is no treatment.
'There's unfortunately now a bit of a culture of, "of course we can fix everything, we've got an antibiotic for anything,"' Dr Mazzarro says.
Disregarding the fact that antibiotic resistance is the next big threat to public health, so we should use the drugs sparingly, antibiotics don't actually do anything for measles because it's a virus - something, Dr Mazzarro says, people often forget.
And combating a virus has never been humans' strong suit.
'With antivirals, we have never been ahead of the game, there aren't many we can treat. A good example is herpes, we have excellent treatment for that, and CMV [closely related to chickenpox]. But that's really about it.'
'The vaccine is the only thing we have' to fight measles, she says, and its success essentially put to bed any programs that might have developed post-measles treatment.
'There wasn't a real urgency to treat it because we were on the verge of eliminating it. People were like "wow this works great, why would you have a research and development program?"'
With the unusual and impressive