Medicine for Policymakers

Medicine for Policymakers is a new Journal column that provides decision makers with brief explanations of the meaning and

implications for biosecurity of clinical issues. The articles describe, for a nonmedical audience, hospital practices, medical

challenges, healthcare delivery issues, and other topics of current interest. Readers may submit ideas to the column’s editor, Amesh

A. Adalja, MD, through the Journal’s editorial office at jfox@upmc-biosecurity.org.

Vaccines, Immunity, Whooping Cough, and Mumps

Amesh A. Adalja

Vaccinations protect people against a variety ofdiseases, but vaccination is not always a panacea, be-

cause its effects are not permanent. Over time, the antibodiesthat are produced by a vaccine—and that protect againstdisease—may decrease in number and may fall below thethreshold needed to protect against infection. Recent out-breaks of whooping cough and mumps are examples inwhich waning immunity from earlier vaccinations coupledwith falling vaccination rates in the population have pro-duced conditions that foster the spread of disease.

Vaccine-induced ImmunityNot PermanentGenerally, 1 to 2 weeks after a person is vaccinated (or hascompleted a vaccine series: some diseases require severalinoculations to build full immunity), his or her immunesystem will have produced enough antibodies to ward offfuture attacks from that organism. For example, if a personwho has received the hepatitis B vaccine series is exposed tohepatitis B virus, he or she cannot be infected by the virus,because the antibodies generated by the vaccine block theability of the virus to infect.

Over time, however, the immunity of the vaccinatedperson may begin to decrease as the time from the lastvaccination increases, and, in some cases, the person’s im-munity may fall below a critical level, thus opening the doorfor an infection to occur. The time frames vary for differentconditions, but this lessening of immunity usually occursover the course of several years.

Remaining partial immunity may protect a person fromcontracting a severe case of the illness, but that individual isstill able to serve as a host for the microbe and may be ableto pass it on to others who are susceptible because they areunvaccinated for any of a number of reasons, including age(ie, being too young to be fully immunized) or personal orparental choice.

Whooping Cough

In recent months headlines have announced the resurgenceof whooping cough (or pertussis) in several states. Whilemost cases are not severe, several children in California havedied from the disease, and several other states are seeingrecord numbers of cases.1 Pertussis is a disease that manypeople consider a relic of history made irrelevant by mod-ern vaccination. However, pertussis is still with us, andseveral factors explain its resurgence.

100 Days of CoughWhooping cough is a contagious disease that is contractedfrom other people by inhaling the bacterium Bordetellapertussis, which is expelled when a person with pertussiscoughs. Both children and adults can be infected with thebacteria and can develop symptoms.2

Whooping cough is characterized by a protracted illnesswhose most common feature is a chronic cough, which canlast so long it is often referred to as a ‘‘hundred day cough.’’

Biosecurity and Bioterrorism: Biodefense Strategy, Practice, and ScienceVolume 9, Number 1, 2011 ª Mary Ann Liebert, Inc.DOI: 10.1089/bsp.2011.0212

9

At times, the cough can be so violent that ribs can befractured during coughing spells. Vomiting after coughingspells also is common.

The more severe manifestations of whooping cough—including pneumonia, which can be fatal—are primarilyrestricted to the very young. The classic ‘‘whoop’’—asound emitted during inhalation after a fit of violentcoughing—may or may not be heard and is more char-acteristic of the disease in children and infants than inadults.3

Vaccination to Combat PertussisPertussis immunity requires a series of 3 initial vaccina-tions, followed by 3 booster vaccinations before age 12.The first is administered to children aged 2 to 6 months inthe same shot with tetanus and diphtheria vaccines (theDPT shot). After completing the series, the child is pre-sumed to be immune. Recently, however, it has beenfound that the immunity induced by the childhood seriesof vaccinations does not endure through adulthood andcan fall below the level needed to protect against infection.Thus, beginning in 2007 it was recommended that adultsunder age 65 should receive a booster shot against per-tussis with their next tetanus/diphtheria shot, which isusually given every 10 years.3 More recently, clinicianshave been advised to move beyond the age 65 cap andoffer the vaccine to all their patients to fully augment adultimmunity to pertussis.4

A Perilous CombinationWhen adults are not fully immunized and contract theillness, they serve as a means for the pathogen to find newvictims who are not immune. These nonimmune indi-viduals include babies too young to be fully immunized—especially those younger than 2 months of age who havenot yet received any pertussis vaccinations—as well asthose with only partial immunity because they have notyet received the full series of vaccinations, other adultswith lapsing immunity, and those who have not beenvaccinated for personal/parental reasons. If pertussis findsan infant as its new host, it can cause an illness that mayultimately be lethal.

The Resurgence of Mumps

The viral disease mumps is characterized by swollen sali-vary glands, and its most serious complications includesterility and meningitis. Mumps, like pertussis, is a fullyvaccine-preventable illness, and full immunity wasthought to occur after a series of 2 vaccinations by age 6.However, several recent outbreaks in the U.S. have raisedthe question of whether a third dose would lessen the

chance of outbreaks caused by waning immunity andgaps in vaccination. In one outbreak, 75% of those whocontracted mumps had received the recommended 2-doseregimen. Although some locales have offered a thirddose of vaccine, the official recommendation remains at 2doses.5

Herd Immunity

Not everybody has to have been vaccinated to preventsustained spread of a contagious disease. When vaccinationlevels in a population reach about 70%, and there are toofew susceptible members left to be infected by a specificmicroorganism, it is said that the population has ‘‘herdimmunity.’’ Herd immunity prevents large outbreaks fromoccurring because the likelihood that a pathogen will findsomeone who it can infect is small as the majority of peopleit comes into contact with are already immune. However, ifherd immunity has faltered—through waning immunity orfailure to vaccinate—susceptible hosts will abound, as is thecase with pertussis.

Vaccination Rates Must Remain High

In order to ensure that diseases that have been controlled byvaccination do not recur and spark new epidemics, it isessential to understand that the effects of vaccines admin-istered in childhood have limits and may need boosting. Itis equally important to realize that vaccination is a crucialpart of promoting the health of the public and that anypockets of the populace that are not immunized will beexploited by pathogens. Therefore, a personal decision torefuse vaccination has implications beyond the individual.When a person declines vaccination, it increases the risk ofinfection for everybody else, including those who are not orcannot be vaccinated.

References

1. Pertussis Report. California Department of Public Health.November 30, 2010. http://www.cdph.ca.gov/programs/immunize/Documents/PertussisReport2010-11-30.pdf. Ac-cessed December 10, 2010.

2. Waters V, Halperin S. Bordetella pertussis. In: Mandell GL,Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett’sPrinciples and Practice of Infectious Diseases. 7th ed. Phila-delphia, PA: Churchill Livingstone; 2010.

3. Kretsinger K, Broder KR, Cortese MM, et al. Preventingtetanus, diphtheria, and pertussis among adults: use of tetanustoxoid, reduced diphtheria toxoid and acellular pertussis vac-cine. MMWR Recomm Rep 2006;55(No. RR-17):1-44. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5517a1.htm. AccessedDecember 10, 2010.

4. Moyer CS. Pertussis vaccine guidelines expand as diseasespreads. American Medical News November 8, 2010. http://

VACCINES, IMMUNITY, WHOOPING COUGH, AND MUMPS

10 Biosecurity and Bioterrorism: Biodefense Strategy, Practice, and Science

www.ama-assn.org/amednews/2010/11/08/prsb1108.htm.Accessed December 10, 2010.

5. Centers for Disease Control and Prevention. Update: MumpsOutbreak—New York and New Jersey, June 2009-January2010. MMWR Morb Mortal Wkly Rep 2010;59(05):59.http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5905a1.htm. Accessed December 10, 2010.

Address correspondence to:Amesh A. Adalja, MD

AssociateCenter for Biosecurity of UPMC

621 East Pratt St., Ste. 210Baltimore, MD 21202

E-mail: aadalja@upmc-biosecurity.org

ADALJA

Volume 9, Number 1, 2011 11