Whooping Cough on the Rise in the US
If you’ve ever sat through the night with a small child sickened by whooping cough (pertussis), you know what fear is. Infants and children with pertussis cough repeatedly until no air is left in the lungs, then suck in air with loud “whoop” as they literally fight for every breath. And recent trends in pertussis incidence should concern every parent: After years of decline, whooping cough is making a comeback in the United States and in other countries around the globe. Why is pertussis – a vaccine-preventable disease – making a comeback, and what can you do to protect your family?
From January 1-August 16, 2014, 17,325 cases of pertussis were reported to U.S. health officials, nearly one-third more than during the same time period in 2013. In 2012, more than 48,000 cases were reported to federal health officials, the highest number since 1955. California was especially hard hit in 2014. In June of that year, public health officials declared whooping cough epidemic in California, where nearly 10,000 cases had been reported since the beginning of the year, more than five times higher than expected.
Need to Know: What is Whooping Cough (Pertussis)?
Pertussis is a respiratory disease caused by infection with a type of bacteria called Bordetella pertussis. The disease is popularly called “whooping cough” because of the violent coughing that can ensue once the bacteria attach to the pharynx and release chemicals that damage the tiny, hair-like structures that normally work to clean the air that passes through your nose and upper respiratory tract (called cilia).
Generally, whooping cough symptoms start much like those of the common cold, with a sore throat, runny nose, low fever, and generally feeling poorly. This phase, called the catarrhal stage, can last for 1-2 weeks.
The characteristic “whooping” cough usually develops about 7-14 days after infection and usually lasts 1-6 weeks, although it may linger for as long as 10 weeks. During this stage, called the paroxysmal stage, the person experiences repeated bursts of rapid coughs. After each one of these bursts, the person often inhales forcibly – yielding the characteristic high-pitched whoop associated with the disease.
Eventually, coughing bouts become less frequent and less severe, and recovery begins. This is the third and final phase of the disease, called the convalescent stage. The convalescent stage generally lasts for 7 to 10 days, although it may last as long as 21 days. Coughs gradually become less frequent and eventually disappear. Another respiratory infection in the next several months, however, may cause a return of paroxysmal coughs.
Symptoms are generally most severe in infants and young children. More than half of infants (less than one year old) who contract pertussis will need to be hospitalized. Older children and adults may experience a severe cough that does not include the characteristic “whoop,” but they can still spread the disease to younger children.
Pertussis spreads easily from person to person when the person coughs, spraying tiny drops of fluid containing the bacteria into the surrounding air. People are most infectious during the catarrhal and paroxysmal stages.
Treatment for pertussis usually involves an antibiotic, rest, and supportive care. Most people eventually recover from a bout with pertussis, although they may need to take time off work and school. However, the disease may be serious and even deadly in infants and older adults.
Normal disease cycles may account for at least part of the resurgence in whooping cough. Pertussis disease tends to cycle, with higher rates of disease occurring every 3 to 5 years. But rates in 2014 – like those in 2012 – are higher than expected during normal cycle. And CDC statistics show a steady upward trend in pertussis cases since the 1990s that's not explained by normal cycles.
The History of the Pertussis Vaccine
That steady upward trend has a lot to do with both the pertussis vaccine itself and vaccination rates. To understand why whooping cough is on the increase, you need to understand a little bit about the history of pertussis disease -- and the vaccines that can prevent it.
Until the pertussis vaccine was introduced in the 1930s, whooping cough was a disease to be feared, especially in infants and young children. Up to 270,000 cases of whooping cough were reported each year in the US and close to 10,000 deaths occurred, mostly in infants, young children, and older adults.
Then, in the 1930s, the first pertussis vaccine was developed. The original vaccine was a “whole-cell” vaccine – meaning that the vaccine is made of whole cells of killed bacteria, suspended in liquid. In the 1940s, the whole-cell vaccine was combined with diphtheria and tetanus toxoids to make the combination DTP vaccine (called DTwP), and its use became widespread. Four doses were given at intervals. The whole-cell pertussis vaccine worked well, preventing most (70-90%) serious pertussis disease. By 1965, the number of annual cases had dropped to less than 10,000 cases per year, and deaths from pertussis disease became rare. In 1976, the lowest number of pertussis cases was recorded: 1,010.
But the vaccine, while effective, caused other problems. Local reactions such as swelling, pain, and redness at the injection site were seen in almost half of the children who received the whole-cell vaccine. A significant number of children experienced more serious reactions, such as fever and seizures; and about 1 out of every 100,000 children who received the vaccine ended up hospitalized because of a serious adverse reaction.
While these problems were minor compared to 10,000 deaths a year from whooping cough, they were still unacceptable. So a new and safer vaccine was developed in 1991. The new vaccine, which is still used today, is an “acellular” vaccine: It contains only part of, not the whole, bacteria. Like the whole cell pertussis vaccine, the acellular vaccine is combined with diphtheria and tetanus toxoids.
Pertussis Vaccination Today
Currently, two pertussis vaccines are used, both of them acellular. Children receive the DTaP (diphtheria, tetanus, and pertussis) vaccine, administered at 2 months and afterwards. Teens and adults receive the Tdap vaccine.
The new vaccine causes fewer reactions, so it’s safer to administer. But the immunity it confers doesn’t last as long. Most research suggests that immunity wanes after about 10 years. And since few teens and adults receive Tdap boosters, many people are thought to be vulnerable about 10 years after they receive their last dose of the vaccine. Recent trends seem to fit that timeframe, as rates of pertussis disease have been rising the fastest in teens about 15 years old, who would have received their last DTaP when they were between 4 and 6 years of age -- 10 years ago.
In addition, DTap doesn’t appear to be as effective as the whole-cell version of the vaccine. In research published in June 2013, investigators from Northern California Kaiser Permanente Vaccine Study Center found that teens who had received 4 doses of DTaP vaccines were at almost 6 times higher risk of pertussis than teens who had received 4 doses of DTwP.
So that’s part of the puzzle. However, a less effective vaccine is only partly to blame for upward trend in cases, including the surge in California and Michigan in 2014. Even if the vaccine is not perfect, it does protect against disease, and it does so safely. But in the hardest-hit communities, many parents are opting not to vaccinate their kids. Unimmunized children are about five times more likely to contract the disease than are children who are immunized.
Once the disease enters a community with a high percentage of unvaccinated children (or adults) it spreads more rapidly, even among previously vaccinated children. In most cases, vaccinated children have a less severe bout of disease. But because infants cannot be vaccinated before two months of age, they are at great risk.
For instance, In November 2014, the northern Michigan upscale town of Traverse City was forced to close a charter school with 1,200 students after whooping cough spread from an infected teacher to 167 students and students in 14 neighboring schools. About 17 percent of parents in the school have signed exemptions waivers for required childhood vaccinations. Grand Traverse County has an opt-out rate about six times the national average. That means not enough children are vaccinated to confer what is known as “herd immunity” (i.e. enough people are vaccinated that the disease cannot take hold).
In sum, most experts agree that the limitations of the acellular pertussis vaccine, combined with more parents choosing not to vaccinate their children, has led to steadily rising rates of the disease over the last 20 years.
Protecting Yourself and Others
Here's how you can help to protect yourself, your children, and others:
- If you have young children, check with your pediatrician to make sure they have received all their vaccinations according to schedule. Infants should receive 4 DTaP injections, one at 2, 4, and 6 months. Boosters should be given at 11-18 months and then again at 4-6 years. A Tdap booster is recommended at 11-12 years.
- Older children and teens may need a Tdap booster. Ask your child’s doctor if your child should receive one.
- If you’re an adult, ask your doctor if you need a Tdap booster shot. It’s the best way to protect yourself and those around you. All adults should receive a booster if they work with, live with, or otherwise interact with children, the elderly, or other vulnerable populations. That includes health-care providers, child-care providers, teachers, librarians, and others.
- If you’re pregnant, ask your doctor about the Tdap vaccine. The National Council on Immunization Practices recommends that pregnant women receive the Tdap vaccine during every pregnancy. To be most effective and safe, the vaccine should be given between 27 and 36 weeks of pregnancy.
- If you live in a high-risk area and you know you or your child has been exposed to the disease, ask your doctor about antibiotics to prevent disease. If your doctor prescribes antibiotics, take them exactly as directed.
Advisory Committee on Immunization Practices. (2012). Vaccines for Children Program. Vaccines to Prevent Diptheria, Tetanus, and Pertussis. Atlanta, GA: Centers for Disease Control and Prevention. Retrieved from http://www.cdc.gov/vaccines/programs/vfc/downloads/resolutions/1012-1-dtap.pdf
Centers for Disease Control and Prevention. (2014). Pertussis (Whooping Cough). Surveillance and Reporting. Available at http://www.cdc.gov/pertussis/surv-reporting.html
Rosenthal S, Chen R, Hadler S. (1996). The safety of acellular pertussis vaccine vswhole-cell pertussis vaccine. A postmarketing assessment. Arch Pediatr Adolesc Med. 150(5):457-60. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/8620224
The Joint Commission. (2011). Tdap Vaccination: Tdap Vaccination Strategies for Adolescents and Adults, Including Health Care Personnel. Retrieved from http://www.jointcommission.org/assets/1/6/Tdap_Monograpgh.pdf