A recent whooping cough epidemic in California has affected 4,223 people and sadly resulted in the deaths of nine young babies. But while some pediatricians are keen to blame parents who don’t vaccinate, the issue is far more complicated than that.
The California epidemic is not the first time a whooping cough epidemic has occurred in recent years and the problem of vaccine waning has been discussed in medical journals for decades.
Vaccine Waning
Vaccinations don’t last for a lifetime. In fact, the duration of the whooping cough vaccine is thought to be only about five years. A Polish study found that only 45 percent of vaccinated eight year olds still had any detectable antibodies to pertussis: "Protective antibody levels were detected in 70%, 58%, and 45% children aged 6, 7, and 8, respectively. It shows that decrease of immunity may cause increasing number of pertussis in children above 5."
This study and others like it led to the introduction of a pre-school booster dose of the vaccine. Given its limited time span, even the booster will have worn off by the time the child is 10 or 12. This is why large numbers of cases are now occurring in previously vaccinated teenagers and parents. They can then spread the infection to newborn babies. Babies aren’t considered immune to whooping cough until they have had three or four doses of vaccine (depending on what country you’re from and what schedule you’re working to). The third dose is given at six months old. The higher danger period is in the first six months of life with the majority of deaths occurring before then, so in fact even if a parent has chosen to vaccinate, which most do, their baby isn’t considered immunized in that riskier period.
Vaccinating Older People
To counter this problem, medical policy makers have begun to advise that new parents be vaccinated with DtaP to protect their babies, in addition to introducing more boosters for teenagers. This is a new policy with the theory of minimizing an infant's exposure to pertussis by vaccinating those around him. However, the makers of one such vaccine, Adacel, say they don’t know if this approach will work: "It is unknown whether immunizing adolescents and adults against pertussis will reduce the risk of transmission to infants."
Vaccine Failure
Another issue is those people who have had all the recommended boosters of vaccine and still get whooping cough. Many people affected in epidemics are already fully vaccinated. For instance, the Star Ledger Newspaper reported on February 11, 2009 that in an epidemic of 21 cases of whooping cough, all had been vaccinated. Another cluster of cases at an Elementary school in which 18 young people got whooping cough, 17 of them had had the five recommended doses of vaccine. In a similar outbreak in England, reported in the British Medical Journal, 85.9 percent of the sufferers had been fully vaccinated with all the recommended injections: "64 children had serological evidence of a recent Bordetella pertussis infection; 55 of these children had been fully immunised. At presentation, children with whooping cough were more likely than others to have whooping, vomiting, and sputum production. Children with whooping cough were also more likely to still be coughing two months after the start of their illness continue to have more than five coughing episodes a day and cause sleep disturbance for their parents.
"Conclusions: For school age children presenting to primary care with a cough lasting two weeks or more, a diagnosis of whooping cough should be considered even if the child has been immunized. Making a secure diagnosis of whooping cough may prevent inappropriate investigations and treatment."
Dr. Kari Simonsen, a pediatrician from University of Nebraska Medical Center, said that the vaccine doesn’t work for one in five people vaccinated and that one in five people who have had the shot still go on to develop whooping cough.
“The efficacy of the vaccine is comparatively low”, she said, “but it’s the best vaccine we can build to date.”
Sub-Clinical Infection
In addition to not working, or waning, the vaccination has changed the clinical presentation of the illness, adding to the risk of transmission. In full whooping cough with its range of symptoms, parents would know to keep their children away from other children and to seek prompt treatment, but vaccinated children can have whooping cough without the symptoms and be capable of spreading it to newborn babies without even knowing it.
A study in Israel, mentioned in a CDC document, found that vaccinated people were "silent reservoirs for infection":
"Vaccinated adolescents and adults may serve as reservoirs for silent infection and become potential transmitters to unprotected infants. The whole-cell vaccine for pertussis is protective only against clinical disease, not against infection. Therefore, even young, recently vaccinated children may serve as reservoirs and potential transmitters of infection."
Although they referred to the whole cell vaccine, the new acellular version is known to be less effective.
A New Type of Whooping Cough
Another reason for epidemics is the fact that pertussis has mutated into another form of the illness, just like bacteria evolve to combat antibiotics and lice become resistant to insecticide head lotions. The Journal of Microbiology reported that a new, stronger, resistant type of pertussis was developing in a highly vaccinated population.
The Journal Vaccine also reported a new form of pertussis:
"Bordetella pertussis isolates not expressing Pertussis Toxin (PT) or Pertactin (PRN) have been collected, for the first time in 2007, in France, a highly vaccinated country with acellular vaccines."
So the problem of pertussis in very young infants is clearly much more complex than whether or not we have all had our boosters.
1. Sources: Slusarczyk J, Dulny G, Nowak K, Krszyna J, Wysokinska T, Fordymacka A, Gzyl A, Janaszek W, Gniadek G: Immunity of children aged 6–8 against pertussis, tetanus and diphtheria. Przegl Epidemiol 2002 , 56:39-48
2. VaccinePlace.com - http://www.adacel-locator.com/index.cfm?FA=protect/adacel/content&S=HOME&P=HowS_pread
3. The Star Ledger, 11th February 2009.
4. The Atlanta Journal Constitution, 22nd March 2009.
5. http://www.bmj.com/content/333/7560/174.abstract
6. http://www.cdc.gov/ncidod/eid/vol6no5/pdf/srugo.pdf
7. Journal of Clinical Microbiology, March 2009, p. 680-688, Vol. 47, No. 3
8. Vaccine, Volume 27, Issue 43, 9 October 2009, Pages 6034-6041.
Joanna is a freelance health writer for The Mother magazine and Suite 101 with a column on infertility, http://infertility.suite101.com/. She is author of the book, 'Breast Milk: A Natural Immunisation,' and co-author of an educational resource on disabled parenting, in addition to running a charity for people damaged by vaccines or medical mistakes. Her 13 year old daughter, Jerrica, had whooping cough when she was a baby.