The Suffolk Health Department is offering free pertussis vaccines after two cases of the once-rare disease were reported in Isle of Wight County.

The disease, which is characterized by a hacking cough followed by a high-pitched “whooping” gasp of air, is on the rise. Once very rare because of successful vaccinations, experts are learning that the vaccines given in childhood may wear off and could require boosters for adults to receive protection.

Pertussis is highly contagious and is caused by a bacteria that attaches to part of the upper respiratory system. Even a fully vaccinated person can catch the disease if he is exposed to it, but the infection usually is less severe after vaccination.

The Centers for Disease Control recommend that adults ages 19 through 64 have a dose of the Tdap vaccine, which also protects against diphtheria and tetanus. In addition, those older than age 65 who have not previously received a dose of Tdap should obtain one, especially if they have contact with infants or young children.

The two cases reported in Isle of Wight County both were students at Isle of Wight Academy. According to the CDC, outbreaks at middle and high schools are common as protection from childhood vaccines fades.

The Western Tidewater Health District provided free Tdap vaccines to faculty and staff at the academy.

Reported cases in Virginia have doubled since 2007, according to the Virginia Department of Health.

“Studies have shown that for every one adult with symptoms of pertussis, there are five adults that show no symptoms,” said Nancy Welch, acting director of the Western Tidewater Health District. “Also, most infants less than 12 months contract pertussis from an adult. That is why a Tdap booster is strongly recommended for older children and adults, especially among those who have contact with infants less than 12 months of age.”

Infants who are too young to be vaccinated are uniquely susceptible and must depend on people around them to provide protection.

The Suffolk Health Department will offer free pertussis vaccines at no cost to eligible individuals, including adults who have close contact with infants or young children and those who are uninsured or underinsured.

The health department is located at 135 Hall Ave. Tdap vaccine walk-in hours are Monday through Thursday from 1 to 3:30 p.m.

For more information, call 514-4782.