Protection against whooping cough drops quickly after children receive their last dose of vaccine, a new study finds. The study focused on children in Minnesota and Oregon. All were born between 1998 and 2003. More than 400,000 of the children received all 5 doses of the DTaP vaccine by age 6. This vaccine protects against whooping cough (pertussis), diphtheria and tetanus. Researchers looked at records on whooping cough cases in the 6 years after the children got their last vaccine dose. Cases went up each year. In the first year after children completed their vaccine series, there were 15.6 cases of whooping cough per 100,000 children in the study group in Minnesota. By the sixth year, the rate was 138.4 per 100,000. In Oregon, whooping cough cases rose from 6.2 cases to 24.4 cases per 100,000. The journal Pediatrics published the study. HealthDay News wrote about it March 11.

By Henry H. Bernstein, D.O.
Harvard Medical School

What Is the Doctor's Reaction?

It is not just the flu causing lots of cough illness in people these days. Pertussis (also known as whooping cough) is on the rise, too.

Early data show that more than 41,000 cases of pertussis were reported last year. This is the largest number of cases for a single year in nearly 60 years, the Centers for Disease Control and Prevention says.

Researchers have been trying to figure out why there are so many more cases of pertussis in the United States. Many believe that outbreaks are happening because:

• There is just more pertussis disease around
• Doctors are recognizing and reporting more pertussis than ever before
• Improved lab testing makes it easier to confirm the disease
• Protection from the childhood pertussis vaccine (DTaP) begins to wear off

A study just published online in the journal the journal Pediatrics tested the theory that the vaccine protection wears off over time. Researchers looked at more than 400,000 children in Minnesota and Oregon who had received all 5 doses of the DTaP vaccine series. They got the fifth dose when they were 4 to 6 years old. Researchers wanted to see if these children continued to be protected for at least the next 6 years.

The study found that the risk of pertussis infection goes up steadily each year after children complete the DTaP series. The study also showed an increase in the number of pertussis cases in children 7 to 10 years old in both Minnesota and Oregon.

In fact, the number of cases went up 6-fold in Minnesota between 2007 and 2009.

This study helps to explain why we are seeing more pertussis in children, even though they have finished their DTaP series on schedule. It appears that by the time children are 7 to 10 years old, protection has dropped off quite a lot.

Though the vaccine may not provide the right amount of protection for as long as initially thought, it still works very well throughout early childhood. Young children still need all 5 doses of vaccine.

What Changes Can I Make Now?

Whooping cough is a very contagious disease that affects the lungs. It causes severe, violent coughing. People with pertussis usually suffer from "coughing fits." This disease makes it difficult for children to breathe.

The best way to protect against pertussis is by getting vaccinated. Before a vaccine was available, pertussis killed about 9,000 people in the United States each year. Now, with the pertussis vaccine, the annual number of deaths is fewer than 20.

Before 2005, children received a different type of vaccine. It provided longer-lasting immunity than the current vaccine appears to offer. However, it had more side effects. The current vaccine was developed in response to those concerns. Vaccines must be both safe and effective. Striking the balance between the two is not always easy.

Teens and adults are often the ones who have pertussis and then spread it around. Newborns and young infants do not handle this disease well. The vaccines may not last forever, but the more people who are up to date with their vaccines, the better for everyone in the community.

Pertussis vaccines are still the best protection we have. They are recommended for all ages.

Young children should get one dose of DTaP vaccine at each of the following ages:

• 2 months
• 4 months
• 6 months
• 15 to 18 months
• 4 to 6 years

Adolescents should get 1 dose of Tdap, another vaccine that protects against pertussis, because the protection from DTaP wears off as children get older. The 1 dose of Tdap is given at:

• 11 or 12 years old routinely
• 13 years or older if the teen has not yet had a Tdap vaccine
• 7 to 10 years old if the child did not get all 5 doses of DTaP vaccine

Adults should get a single dose of Tdap if they have never received it before.

Pregnant women and all close contacts of infants should get a single dose of Tdap. Infants are at greatest risk for getting pertussis because they are too young to be fully protected by the vaccine. They are also more likely to have severe health problems and even die from pertussis.

• Pregnant women should be vaccinated with Tdap during each pregnancy. This way the mother builds up protection to pertussis and gives it to her newborn.
• Close contacts of infants should be vaccinated with Tdap. This includes parents, siblings, grandparents, other family members, babysitters and caregivers. Each person should get the age-appropriate pertussis vaccine (DTaP or Tdap). This should be given at least two weeks before they come into close contact with the infant.

What Can I Expect Looking to the Future?

Experts want to know why protection seems to wear off after people receive DTaP or Tdap vaccines. They want to figure out how to make a better vaccine.

Researchers will continue to assess how much pertussis there is among children in the United States. They also will monitor how effective the vaccine is in protecting against pertussis.

Expect to hear more about the importance of whooping cough vaccinations from your child's doctor. Make sure that that your child is up to date with all vaccines, including pertussis. Make sure you are up to date as well.