CHICAGO (CBS) — Students entering grades 6 and 9 in Illinois have until Oct. 15 to be vaccinated for whooping cough.

As WBBM Newsradio’s Lisa Fielding reports, state Department of Public Health spokeswoman Melaney Arnold says starting this year, for the first time, students will need to show proof they have received the Tdap vaccine.

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LISTEN: WBBM Newsradio’s Lisa Fielding reports

The vaccine is a booster shot against diphtheria, tetanus, and pertussis – the technical name for whooping cough.

“For entering 6th graders, they are required to have a physical exam for school entrance, so we tried to coordinate it with that time,” Arnold said. “For those who are entering 9th grade, we wanted to make sure that we captured that high school population, so this is something they are going to go and have to have done.”

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The requirement comes as Illinois has seen an increase in whooping cough cases. About 1,200 cases of whooping cough have been reported in Illinois so far this year, by comparison to 468 as of Aug. 1 of last year.

Pertussis is a contagious bacterial infection that causes a range of symptoms. It is easily spread through coughing and sneezing.

Symptoms may appear 5 to 10 days after exposure but can take three weeks to show up. Initial symptoms are similar to those of a common cold but after a week or two can develop into bursts of numerous, rapid coughs with a distinctive “whooping” sound.

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While it can be mild in some cases, it poses a greater risk to infants who are not fully immunized, those with compromised immune systems and older people.