CHICAGO (WGN) — About 90% of the U.S. population has gotten their two-dose regimen to protect against measles, mumps and rubella, but, the unvaccinated have increasingly been contracting the highly contagious, deadly disease. Northwestern University and Lurie Children's pediatric infectious dis ease specialist Dr. Ravi Jhaveri warns that without proper coverage, storm clouds ahead have him worried. "I like to have people think about vaccines as an umbrella, and the idea is an umbrella doesn’t necessarily keep you from getting wet, but it keeps you from getting soaked," he said. "We see periodic outbreaks of measles because it’s a very highly contagious agent, and even modest drops in the amount of protection amongst communities can lead to outbreaks." Measles cases rise to about 320 total in Texas and New Mexico. What you should know. Decades of research have proven the MMR vaccine is 95% effective after the first dose. Experts say now it is more critical than ever to know protection level and potential threat. "More than 90 percent of parents are having their kids vaccinated on time with the appropriate doses by the time their kids enter kindergarten, and so I want to make sure we recognize them for the effort they are doing," Jhaveri said. The measles vaccine comes in two doses, working in stages to combat a virus that can linger in the air for hours after an infected person coughs, sneezes or even talks. The respiratory infection leads to fever, cough, inflamed eyes, mouth sores and a skin rash. "We know with an agent like measles, that’s very contagious, that 95 percent wasn’t enough, and so that led to the outbreak of cases in the late 80s and 90s, so we then instituted a second dose to try to make sure we cover the population well so even that five percent that didn’t respond to the first dose was captured and covered with second dose," Jhaveri explained. Eventually, for convenience, doctors and parents began giving the second dose to children at age 4. Jhaveri said the move became more practical and effective. But as measles spreads now, should parents be concerned if their child only got one shot? "You are definitely going to be protected partially. One dose is better than no doses, and two doses is better," Jhaveri said. March 14 | More than 300 measles cases now confirmed in 14 states For those teenaged to adulthood, the two doses are far in the rearview mirror. And since the virus is one of the most contagious, with 9 out of 10 people exposed to an infected person likely to get sick, doctors can see a situation where greater illness is in sight, even for the vaccinated. "You should talk to your doctor about making sure you have up-to-date vaccines with the current guidance and we are airing on the side of extra doses," Jhaveri said. That's why the MMR shot is so critical for children to render the population with herd immunity. As for adult boosters, Jhaveri said the population isn't necessarily at risk, but "if you are close to an outbreak or could be exposed if you work in a healthcare setting, we err on the side of extra doses." Rising vaccine hesitancy has health experts concerned about other illnesses as well, including chicken pox and potentially polio. ...read more read less