Certain diseases from which most people are vaccinated for are beginning to make a comeback in some parts of the country, leaving health officials watchful.

“We, in the big picture, are seeing a resurgence of some of the vaccine-preventative diseases,” said Peter Troell, a medical epidemiologist with the Fairfax County Health Department. Measles and pertussis, or whooping cough, are the most prevalent, he said.

Although Fairfax County has not had a documented case of measles for about a decade, cases have occurred in which someone who was working, traveling through or seeking medical treatment within the county has exposed residents to measles, Troell said.

About a dozen measles cases have been reported in the region since 2008, he said. The most recent exposure occurred last month, when a passenger on a train was found to be infected with measles. The train made stops in the county while traveling from Boston to Richmond.

“Now you are more likely to come in contact with it, so being vaccinated is just that much more important,” Troell said.

Because the measles vaccine remains very effective, infections almost always are seen in people who have never been immunized, Troell said. It is especially important for people who intend to travel internationally to ensure that they are immunized to measles, he added.

Whooping cough also is on the rise nationally, with major outbreaks in California, Michigan and Ohio occurring during the past two years, according to the Centers for Disease Control and Prevention.

Virginia saw a 72 percent spike in reported pertussis cases between 2009 and 2010, according to the Virginia Department of Health. Between 2000 and 2009, there was an average of 262 cases of pertussis in Virginia each year, with another spike in cases occurring in 2004 and 2005.

“Although pertussis traditionally occurs in cyclical peaks, the two-fold increase in Virginia since 2007 is cause for concern,” State Health Commissioner Karen Remley said in a statement this spring.

Fairfax County has not seen a spike in the illness, and typically sees 30 to 40 cases of it annually, Troell said. Vaccination remains an essential tool in preventing larger outbreaks.

“Given the fact that we’re seeing this increase in some places … there is a distinct possibility to see it in other places as well,” he said.

A small outbreak of whooping cough earlier this year in Floyd, in southwest Virginia, was linked to a lack of vaccinations among students at one private school.

With pertussis, a greater problem exists among people whom have been immunized, or partially immunized, contracting the disease, Troell said. If properly administered, the vaccine is about 80 percent effective, according to the CDC.

Like most school systems, Fairfax County requires students to be up-to-date on vaccines before enrolling in classes each year.

In addition to the five-shot series children receive by age 7 to develop initial immunity to pertussis, health officials recommend children receive a booster shot at 12. Fairfax County public schools require students receive the Tdap booster for tetanus, diphtheria and pertussis to enter sixth grade. Parents can request a waiver because of religious beliefs or if the vaccination would harm the child’s health.

Adults who might have missed out on getting the booster, which became a requirement in the mid-2000s, should consider requesting the Tdap booster, instead of the regular tetanus shot, Troell said.

“Pertussis can be severe in adults,” he said. “You get a cough that can last for a very long time.”

The disease can have much worse effects in children, especially those who have not yet received the full series of shots and may only have partial immunity, Troell said.