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The Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) classify more than 2 dozen diseases as vaccine preventable or potentially preventable.[1,2] However, the incidence of these diseases has been rising in recent years—even in countries with a high standard of living and universal access to vaccines. In the United States, outbreaks of vaccine-preventable diseases often occur as a result of nonimmunization or underimmunization among children and adults, as well as from exposure to infections brought into the country by unvaccinated travelers who visit and return from high-risk or endemic regions.
Since 2008, the Global Health Program (GHP) at the Council on Foreign Relations (CFR) has tracked global outbreaks of measles, mumps, polio, rubella (German measles), whooping cough, and other vaccine-preventable diseases (eg, chickenpox, cholera, diphtheria, meningitis, rotavirus, typhoid), as well as attacks against vaccination teams.[3] The CFR interactive map (http://www.cfr.org/interactives/GH_Vaccine_Map/#map) plots the outbreaks by year (from 2008 onward) and by region, provides the estimated numbers of cases, as well as uses relative visual measurements (not to scale). It is important to note that disease outbreaks may largely go unreported in underdeveloped regions.
This slideshow will focus on the reemergence and characteristics of measles, mumps, rubella, pertussis, and polio. The image shows the global immunization coverage of six vaccine-preventable diseases in 2013.
Images courtesy of the World Health Organization (WHO) (adapted chart), CDC (DTP3, polio, measles), Medscape (hepatitis B), R Duperval, MD (pneumococcal), and CDC/ Dr Erskine L. Palmer (rotaviruses).
Community or herd immunity refers to the indirect protection of unimmunized individuals against certain contagious diseases from exposure to a percentage of immune persons in a population (ie, the spread of disease is limited) (shown).[4-7] The proportion of a population that needs to be vaccinated (vaccination rate) to provide community immunity is known as the herd immunity threshold (HIT), and it varies depending on the disease.[5-7]
When the vaccination coverage for a particular contagious disease achieves or exceeds the HIT in a population, most of the individuals in that population, even those few who are not fully vaccinated or who are unable to be vaccinated, will be protected against that disease. Consequently, person-to-person spread of the disease will be contained, because there are not enough susceptible people in the community, and the risk of an outbreak of that disease is significantly reduced.
Adapted image courtesy of the National Institute of Allergy and Infectious Diseases (NIAID).
In contrast, when a large percentage of the population is unvaccinated, the entire group is more susceptible to contagious diseases (shown). For example, the United States has high immunization rates overall, but there remain regions with low vaccination rates where outbreaks of vaccine-preventable diseases can and do occur.[8] Thus, in effect, "herd immunity is generally only as good as the vaccine coverage in a given area."[8]
Note, however, that it is difficult to determine a minimum HIT, because it depends on the infectivity of the agent and the heterogeneity of the populations.[6] From a public health perspective, the target is 100% vaccine coverage. Data for the most contagious vaccine preventable diseases (eg, measles) suggest at least a 50% population coverage may be required.[6]
Adapted image courtesy of NIAID.
Globally, an estimated 20 million cases of measles (rubeola) occur each year.[9] In the United States, although measles has been a vaccine-preventable disease since 1963 and it was declared eliminated from the country in 2000, cases continue to be imported from other countries, and low vaccination rates have allowed domestic spread of these imported cases.[10] In 2014, the reemergence of measles prompted a warning from US health officials. CDC investigators were and remain concerned that worldwide anti-vaccination campaigns are resulting in a serious comeback of measles and other vaccine-preventable diseases. Two outbreaks in particular caused concern, and they illustrate the vulnerability of unvaccinated populations to the importation and domestic transmission of highly contagious illnesses such as measles.
In March 2013 an intentionally unvaccinated 17-year-old from New York City visited London and contracted measles.[11] After the teen returned home, a total of 58 cases of measles were identified in two orthodox Jewish communities with low rates of vaccination. Moreover, officials from the New York City Department of Health and Mental Hygiene (DOHMH) traced 3500 contacts and documented 6 generations (person-to-person spread) of infection. No cases occurred in vaccinated people but, significantly, 21% of the cases were in infants who were too young for the recommended measles/mumps/rubella [MMR] vaccine.[11]
In 2014, there were a record 668 US measles cases from 27 states, mostly in unvaccinated travelers to endemic regions or to areas experiencing a large, ongoing measles outbreak.[12] This was the highest number of cases since eradication was declared in 2000. The largest outbreak occurred in unvaccinated Amish communities in Ohio, totaling 383 cases.[12]
From January 1 through April 24, 2015, the United States has experienced 5 outbreaks, with 166 cases reported (shown).[12] Preliminary investigations of a large multistate outbreak that originated in California revealed 45% of the infected were unvaccinated, and 43% had unknown vaccination status.[12]
Image courtesy of the CDC.
As demonstrated in the previous slide, measles is one of the most contagious infectious diseases in humans, with a greater than 90% secondary attack rate among susceptible close contacts.[10,14] This disease is caused by the rubeola virus (family Paramyxoviridae, genus Morbillivirus) and is transmitted primarily through the air by breathing, sneezing, and/or coughing.[10,14,15] Infected individuals are usually contagious before they develop symptoms/signs (ie, about 4 days before to 4 days after rash onset).[10] Symptoms/signs include a generalized macular, blanching rash; fever; conjunctivitis; malaise; rhinorrhea; and cough.[10]
Dermatologic manifestations of measles include red spots whose diameters range from 0.1 to 1.0 cm (shown) and that appear on the day 4-5 following the onset of symptoms. The nonpruritic measles rash usually coincides with the appearance of a high fever (≤40.6˚C or ≤105°F).[10] It begins on the face at the hairline, and it spreads downward to the neck and trunk (shown).[16] Within 36 hours, it can spread over the entire trunk and extremities (although it often spares the palms and soles). The spots may coalesce, most often in facial areas. The rash usually begins to fade 3-4 days after it first appears.[16]
Image courtesy of DermNet NZ.
In the prodromal or beginning stages of measles, one of the signs of the onset of infection is the eruption of Koplik spots on the buccal mucosa and tongue.[6,18] These lesions appear as irregularly shaped bright red spots, often with a bluish-white central dot.[6,18] It is important to recognize Koplik spots, because they may be the only indication of a measles diagnosis during the nonspecific prodromal phase.
Peak transmission of measles occurs in the late winter and early spring in temperate climates; in tropical climates, it is after the rainy season.[15] Epidemics may occur every 2-3 years, depending on local vaccination coverage rates.[15]
Approximately 30% of measles cases lead to the development of serious complications,[16] including pneumonia, meningitis, hospitalization, and even death.[14] Approximately 1-2 of every 1000 infected children worldwide die from respiratory and neurologic complications of measles.[14] However, public health strategies that include routine pediatric measles vaccination as well as mass immunization campaigns in regions with low vaccination rates has led to a 75% global reduction in measles deaths (2000: 544,000 deaths; 2013: 146,000 deaths).[19]
Recommended routine vaccination with the MMR vaccine (age ≥12 months): A two-dose series administered at ages 12-15 months and 4-6 years.[20] The second dose may be given before age 4 years if the interval between the first and second doses is at least 4 weeks.
Image courtesy of the CDC.
In 2004, the United States verified the elimination of rubella (German measles) and congenital rubella syndrome (CRS) in the country, and on April 29, 2015, the Pan-American Regional Office of the World Health Organization (PAHO/WHO) announced that the Americas region is the world's first region to eliminate rubella and CRS.[21] However, a small percentage of the population in these areas remains at risk for the disease and sporadic outbreaks still occur, usually as a result of importation from endemic regions.[22]
Infection with the rubella virus (family Togaviridae, genus Rubivirus) generally causes mild disease in children and young adults; up to 50% of those affected may be asymptomatic.[23] As with measles, rubella transmission is via respiratory secretions. The nonspecific maculopapular, generalized red rash (shown) appears 14-17 days after exposure, may last up to 3 days, is occasionally pruritic, and has a similar appearance to that of measles, spreading from head to foot.[23] Unlike measles, however, rubella is less contagious, is less severe, and has a shorter duration. Prodromal signs/symptoms that may precede the appearance of the rash include low-grade fever, malaise, mild conjunctivitis, rhinorrhea, and pharyngitis.[22]
Image of the maculopapular, generalized rash of rubella on a patient's abdomen courtesy of the CDC.
Rubella infection in pregnant women can have severe adverse consequences on the unborn child; this is known as CRS. Serious complications and birth defects include vision and hearing loss, cardiac defects, neurologic abnormalities, and liver or spleen damage.[23] Rubella infection during pregnancy can also result in miscarriage, premature delivery, and death of the fetus.
The Measles & Rubella Initiative is a global partnership among the American Red Cross, CDC, United Nations Children's Fund (UNICEF), United Nations Foundation, and WHO.[24,25] Through vaccination efforts and operational/technical support, their goal is to reduce global measles deaths by 95% in 2015 and to eliminate measles and rubella in five of six WHO regions by 2020.[25]
The image shows an infant who was born with multiple blue/purple cutaneous marks/nodules known as "blueberry muffin syndrome."[26] CRS is one of the many causes of this dermatologic manifestation.
Image courtesy of DermNet NZ.
Mumps is a highly contagious acute viral infection (family Paramyxoviridae, genus Rubulavirus) that occurs in the parotid salivary glands.[27,28] Viral transmission occurs through saliva, nasal secretions, and close personal contact. Symptoms/signs typically appear between 14 and 16 days to 18 days after infection and consist primarily of a low-grade fever, malaise, myalgia, loss of appetite, and headache. Up to 30% of cases are asymptomatic.[28]
In 30%-40% of patients, the illness is characterized by unilateral/bilateral edema primarily affecting the parotid gland, although the submandibular and sublingual glands may also be involved (shown).[27] Symptoms of trismus may also occur secondary to parotid gland swelling. In general, the symptoms decrease within 7 days and resolve by 10 days.[27]
Image courtesy of the CDC/Patricia Smith and Barbara Rice.
Although mumps rarely causes death, complications from mumps may include meningitis, encephalitis, hearing loss, orchitis, oophoritis, pancreatitis, and myocarditis.[28]
Over the past few years, sporadic outbreaks of mumps have been reported in several countries, including clusters in the United States, Canada, Vietnam, and Australia, as well as epidemics in the United States, United Kingdom, Germany, Spain, Macedonia, Israel, Egypt, Serbia, the Netherlands, Colombia, and Guam.[3] Factors that may be associated with these outbreaks include misdiagnosis, vaccine failure, inadequate levels of vaccination, and potential antigenic differences in mumps virus strains between the outbreak and those related to the vaccines.
Note that although vaccinated people have contracted mumps during outbreaks, they did so at a much lower rate than the unvaccinated. Current estimates of the MMR vaccine efficacy are 88% (66%-95%).[29]
Image courtesy of the CDC.
Of all the vaccine-preventable diseases in the United States, pertussis (whooping cough) is the most poorly controlled, with peaks in disease occurring every 3-5 years.[31] This highly contagious disease is caused by the bacterium Bordetella pertussis, it is spread via respiratory secretions, and it is treated with antimicrobial agents such as azithromycin.[32]
Pertussis is divided into three stages: catarrhal, paroxysmal, and convalescent.[33] Once infection occurs, the initial catarrhal stage in the first 7-10 days may be indistinguishable from a routine upper respiratory tract infection with symptoms/signs of coryza, low-grade fever, and an occasional cough that gradually becomes more severe. As the illness progresses into the second, paroxysmal, phase, which last an average 1-6 weeks, patients often experience paroxysms of multiple, rapid coughs (shown) accompanied by an inspiratory high-pitched "whoop" at the end of the paroxysms. They may also exhibit cyanosis, vomiting, and exhaustion. The paroxysmal attacks frequently occur at night, with an average of 15 attacks per 24 hours.[33]
In the convalescent stage, the cough gradually becomes less paroxysmal and resolves in 2-3 weeks; however, for several months after the initial infection, recurrence of the paroxysms often accompany subsequent respiratory infections.[30,33]
Image courtesy of the CDC.
In unvaccinated or incompletely vaccinated infants (age <12 months) and young children, pertussis can cause life-threatening complications.[33] An estimated 50% of infants with pertussis who are younger than 12 months are hospitalized, of whom 67% will have apnea, 23% will develop pneumonia, 1.6% will have seizures, 1.6% will die, and 0.4% will have hypoxic or toxin-induced encephalopathy.[34] Anorexia, dehydration, insomnia, epistaxis, hernias, otitis media, and urinary incontinence may occur. In addition, more severe complications may include refractory pulmonary hypertension, pneumothorax, rectal prolapse, and subdural hematomas.[34]
In one study, the most common pertussis complications among adults were weight loss (33%), urinary incontinence (28%), and syncope (6%), as well as rib fractures and subconjunctival hemorrhages (shown) from severe coughing (4%).[35]
Image courtesy of Wikimedia Commons/Raul654.
Following the widespread availability of the pertussis vaccine in the United States from the 1940s till 1970, the average annual number of reported pertussis cases dropped by nearly 98% (from about 200,000/year to <5,000/year).[30] Overall, there has been an 80% reduction in the incidence of pertussis following the advent of the vaccine compared to the prevaccine era.[36] However, from the 1980s to the present, the number of annually reported cases of pertussis has increased,[30,36] with many outbreaks linked to large numbers of unvaccinated children. In 2012, there were 48,277 US cases, with many more unrecognized and unreported.[37]
Recommended routine vaccination with the diphtheria and tetanus toxoids and acellular pertussis (DTaP) vaccine (age <7 years): A five-dose series administered at ages 2, 4, 6, and 15-18 months and 4-6 years.[20] Do not give the vaccine earlier than age 6 weeks. The fourth dose can be administered as early as age 12 months if there has been at least a 6-month interval from the third dose. It is not necessary to repeat the fourth dose if it was given at least 4 months after the third DTaP dose (ie, the fourth dose does not need to be repeated after the 6-month interval between doses 3 and 4).[20]
Recommended routine vaccination with the tetanus and diphtheria toxoids and acellular pertussis (Tdap) vaccine (age ≥7 years): A single dose of the Tdap vaccine at ages 11-12 years, regardless of the interval between the last tetanus and diphtheria toxoid-containing vaccine. For pregnant adolescents, administer a single dose of Tdap for each pregnancy (preferred: 27-36 weeks' gestation), regardless of when the last tetanus/diphtheria toxoid (Td)-containing vaccine was given.[20]
Image of an infant who is being treated for a severe pertussis infection courtesy of the CDC.
In the years following completion of the five-dose DTaP vaccine series in children, the risk of contracting pertussis steadily increases, likely attributable in part to waning immunity from the vaccines.[38] This waning immunity, combined with increased surveillance and reporting of pertussis to public health departments, increased awareness and improved recognition of pertussis among clinicians, and greater access to and use of laboratory diagnostics (especially polymerase chain reaction [PCR]) has likely contributed to the rise in number of reported pertussis cases.
Image of the same infant as in the previous slide courtesy of the CDC.
Poliomyelitis (polio) is a highly infectious and potentially fatal disease caused by poliovirus types 1, 2, and 3 (family Picornaviridae, genus Enterovirus), which invade the nervous system.[39,40] Person-to-person spread occurs via a fecal-oral or oral route. The incubation period is generally 6-20 days.[40]
Of individuals infected with the polio virus, between 72%[9] and 95%[40,41] will be asymptomatic, and about 25% will have minor symptoms/signs that last 2-5 days and then resolve (eg, fatigue, back/neck, stiffness, headache, fever, nausea, flu-like symptoms, abdominal pain, transitory pain in the limbs).[39-41] Fewer than 1% of polio cases result in permanent paralysis of the limbs, usually affecting the legs; of those paralyzed, 2%-10% die when the respiratory muscles are affected.[39] Mortality increases with age.[40]
Although two types of polio vaccines exist—inactivated polio vaccine (IPV) and oral polio vaccine (OPV)—since 2000, only IPV has been used in the United States. However, OPV (shown) is still administered throughout much of the world. Aggressive vaccination campaigns have greatly reduced the global incidence of polio.[42]
Recommended routine vaccination with IPV (age <18 years): A four-dose series at ages 2, 4, and 6-18 months and 4-6 years. The first dose can be given as early as age 6 weeks; the final dose should be given on/after the fourth birthday (≥6 month after the previous dose).[20]
Image courtesy of the CDC.
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