CDC Immunization Schedule and the Facts About Vaccines

2.0 ANCC Contact Hours AACN Category B


At the conclusion of this activity, the learner will be prepared to:

  1. Recall the current nationwide and worldwide statistics regarding immunizations
  2. Demonstrate examples of the efficacy of immunizations in reducing morbidity and mortality
  3. Identify the components of the recommended immunization schedules for children and adults in the U.S. per the Centers for Disease Control and Prevention (CDC)
  4. Discuss the safety of various immunizations during pregnancy
  5. Evaluate the use of immunizations in such worldwide epidemics as dengue fever, malaria, and cholera
  6. Report on the phenomenon of vaccine hesitancy and the emergence of the Antivaxxer Movement 

            The World Health Organization (WHO) makes the assertion that immunizations or vaccines (these terms will be used interchangeably throughout this learning experience) are the single most cost-effective health intervention. Immunizations prevent 2-3 million deaths per year worldwide, and if coverage improves the prediction is that it could prevent 1.5 million more (WHO, 2018c). In 2017, the global coverage for vaccines was estimated by the WHO at roughly 85%. They estimated that almost 20 million children worldwide under the age of one did not receive the recommended three doses of diphtheria, tetanus, and pertussis (DTaP) vaccine. Vaccines can prevent various illnesses from the influenza virus and diarrhea to cervical cancer and paralysis related to polio (WHO, 2018b).  Polio, for example, was once common and has now been nearly eliminated via immunization efforts worldwide. It exists now in just a few small regions of Pakistan, Afghanistan, and Nigeria, with less than 30 cases reported in 2017 (WHO, 2018c).

            The effectiveness of immunizations varies from vaccine to vaccine and from condition to condition. Some, such as the polio vaccine as stated above, are very effective at eradicating disease. Others are simply an adjunctive tool in a large public health toolbox. The meningitis A vaccine, which was introduced in 2010 in sub-Saharan Africa, has led to near elimination of that infection in less than ten years. The immunization campaign for tetanus has led to the elimination of maternal and neonatal tetanus infections in three regions worldwide- the European region, South-East Asian region, and the Americas. The Americas region was also declared the first region to eliminate measles in 2016 (WHO, 2018c). The original vaccine against Streptococcus pneumoniae, called PCV7, was introduced in the U.S. in 2000 and in Africa in 2009. The vaccine was then upgraded to include more serotypes, renamed PCV13, and reintroduced in 2010/2011. Rates of pneumococcal infections in South Africa in children under the age of two decreased from a rate of 54.8 cases per 100,000 person years prior to the vaccination (2005-2008) to just 17 cases per 100,000 person-years after (2011-2012) thanks to a vaccination coverage of 81% in 2012 (von Gottberg et al., 2014). The outcome of introducing new vaccines can be measured in real shifts or changes in medical care trends and outcomes. The varicella vaccine (Varivax or VAR) was introduced in the US in 1995, with 89% vaccine coverage nationwide by 2006. Zostavax (ZVL) is a live attenuated vaccine that was introduced in 2006 for herpes zoster or shingles, a secondary infection related to the same virus. While the VAR vaccine is recommended for children, the ZVL vaccine is recommended for people over age 60. A study published in 2017 found that between 2006 and 2013, there was a 39% decrease in emergency department visits for infection with the herpes zoster virus in folks under age 20 (who would be covered by the VAR vaccine) and an 11% decrease over the same time for people over age 60 (covered by the ZVL vaccine), but a 23% increase in people ages 20-59 who would not be a candidate for either vaccine. The authors felt confident that this trend in decreased utilization of costly emergency department resources was related to effective immunizations in the younger and older age groups over that time (Dommasch, Joyce & Mostaghimi, 2017). In southern China, a cross-sectional ecological study saw that incidence rates decreased and the age of onset increased as an oral rotavirus vaccination (RV) was introduced in that area (Fu et al., 2018). Closer to home, two separate studies have shown encouraging trends related to cervical cancer since the 2006 introduction of the controversial vaccination for human papillomavirus (HPV). A retrospective cohort study done between 2007 and 2014 across 16 clinics serving predominantly low-income and minority populations showed a decrease in abnormal cervical cytology. The detection rate for vaccinated girls (at least 1 dose, ages 11-20) decreased to 79.1 per 1000 person-years, versus a rate of 125.7 per 1000 person years amongst those not vaccinated. This effectiveness was seen most obviously amongst those who initiated the vaccine series between the recommended ages of 11-14 and received all three doses (Hofstetter, Ompad, Stockwell, Rosenthal & Soren, 2016). Similarly, Benard et al. (2017) found a decrease of cervical intraepithelial neoplasia (CIN) amongst girls aged 15-19 in New Mexico over the same period. The incidence per 100,000 women screened decreased from 3,468.3 in 2007 to 1,590.6 in 2014 for CIN1, from 896.4 to 414.9 for CIN2, and from 240.2 to 0 for CIN3. The study found a similar significant decrease in CIN2 lesions amongst women ages 20-24, but an increase in CIN1 and CIN3 lesions amongst women aged 25-29, who would not have had the benefit of vaccination prior to age 14 as recommended (Benard et al., 2017). The effectiveness of vaccination as a public health tool to prevent disease, disability, and death is indisputable.

Immunization Schedule

            The immunization recommendations and schedule in the U.S. is put forth by the Centers for Disease Control and Prevention (CDC). The childhood immunization schedule (Figure 1) can be seen below: 

Figure 1: CDC Recommended Child & Adolescent Immunization Schedule, United States, 2019

            HepB is a vaccination against the hepatitis B virus, which attacks the liver. WHO estimates global coverage for this vaccination at 84%, but within the recommended first 24 hours of life it is only 42%. It is currently available in 187 countries (WHO, 2018b). The CDC recommends 3 doses: one at birth, 1-2 months, and finally again at 6-18 months (CDC, 2019a).

            RV is an oral vaccination against rotavirus, which according to WHO is the most common cause of diarrhea worldwide. Unfortunately, this vaccine is only currently in 85 countries plus 6 partial countries, with a global coverage of 28% (WHO, 2018b). Diarrhea was the 4th leading cause of death worldwide in children under the age of 5 with roughly 500,000 deaths in 2015. Rotavirus was responsible for 29% of these, or 146,500 deaths. The good news is that mortality related to diarrhea has decreased 65% since 1990, mostly secondary to sanitation, clean water, and nutrition advances worldwide. In addition to these lifestyle changes, the RV vaccination has also made quite an impact. The WHO recommended RV in the European and Americas regions in 2006, then worldwide in 2009. In 2016 the rotavirus death rate under age 5 decreased further to 128,500 worldwide, with 104,733 in sub-Saharan Africa. It is estimated that RV saved roughly 28,000 children under the age of 5 in 2016, but expansion of this vaccine could save 20% of all those deaths attributable to diarrhea in children under 5 (Troeger et al., 2018). The CDC recommends two doses of Rotarix at 2 and 4 months or 3 doses of RotaTeq at 2, 4, and 6 months old (CDC, 2019a).

            DTaP is the childhood vaccination against diphtheria, tetanus, and pertussis. Diphtheria is an infection of the nose and throat caused by a bacterium that can lead to difficulty breathing, heart failure, paralysis, and even death. Tetanus is an infection also caused by a bacterium toxin that affects the nervous system and can lead to lockjaw, difficulty breathing, and death. Pertussis, or whooping cough, is a respiratory infection that is caused by a bacterium. It is recommended as five doses at ages two months, four months, six months, 15-18 months and a final booster at four to six years old in the U.S. (CDC, 2019a). The vaccine underwent a change in  the late 1990’s to acellular pertussis due to safety concerns. Then in 2005, a fifth booster dose with lower concentrations of the three toxins was added. Vaccine coverage in the U.S. in 2015 was 95% for three or more doses, 85% for four or more doses. Effectiveness for the series of five is 88.7% against pertussis, but wanes over time. Following this, a tetanus, diphtheria, and acellular pertussis (Tdap) booster is recommended again at age 11-12. Coverage in 2015 in the U.S. was 86% in 13-17-year-old adolescents. In adults (see Figure 2 below) who did not receive a Tdap booster as an adolescent, it can be given once as an adult, followed by a tetanus diphtheria (Td) vaccine every ten years after that (CDC, 2019a). For women, this vaccine was recommended in 2012 to be given during each pregnancy to help protect the fetus and newborn, who are especially susceptible to pertussis infection during the first eight weeks of life (Liang et al., 2018). The CDC recommends Tdap be given between 27-36 weeks gestation (CDC, 2019a). As an alternative to vaccinating pregnant women, a randomized clinical trial tested the use of an acellular pertussis vaccine in newborns under five days old, and found no safety issues with this. They found statistically significantly increased IgG levels against pertussis in the newborns who received the vaccine through ten weeks, but there was some concern that they found decreased IgG levels for other vaccines at 32 weeks of age, calling into question immune interference from an additional vaccine (Wood et al, 2018).

            Haemophilus influenzae type b (Hib) is a bacterial infection that can cause meningitis or pneumonia as well as otitis media, epiglottitis, bronchitis or cellulitis. The vaccine is currently available in 191 countries with an estimated coverage of 72% worldwide and 91% in the region of the Americas (WHO, 2018b). In the U.S., the CDC recommends a four-dose regimen at ages two months, four months, six months, and 12-15 months for most brands, or a three-dose series omitting the 6-month dose if using PedvaxHIB (CDC, 2019a).

            PCV13 is a conjugate vaccine against 13 different pneumococcal bacteria that can cause meningitis, pneumonia, febrile bacteremia, otitis media, sinusitis, or bronchitis. It is currently available in 130 countries plus 5 additional countries partially, but coverage is only 44% worldwide (WHO, 2018b). In the U.S., this vaccine is recommended in infants at ages two months, four months, six months, and 12-15 months. It is also recommended in adults over the age of 65 (see Figure 2 below), or adults with certain immunocompromising conditions that place them at increased risk. A related vaccine, PPSV23, is a 23-valent pneumococcal polysaccharide vaccine introduced in 1983 that is recommended for adults over the age of 65, but should not be given at the same time as PCV13 (they can be safely given 12 months apart with PCV13 recommended first). In additional to adults over 65, PPSV23 is also recommended in children over the age of two and adults with certain chronic medical (heart disease, diabetes mellitus, etc.) or immunocompromising conditions (sickle cell, chronic renal failure, etc.) at least 8 weeks after PCV13 (CDC, 2019a; Jin, 2015).

           The inactivated polio vaccine (IPV) is an injectable immunization to prevent poliomyelitis, which can lead to irreversible paralysis. According to the WHO, coverage for the polio vaccine is 85% worldwide (WHO, 2018b). As previously mentioned, the worldwide campaign to eradicate polio has been especially successful, leaving just a small pocket in a few countries (WHO, 2018c). In the U.S., the injectable vaccine is recommended in four doses at ages two months, four months, 6-18 months and a final booster at four to six years (CDC, 2019a).

           The influenza vaccine is available in multiple forms: an inactivated vaccine (IIV), recombinant (RIV) or live attenuated (LAIV). The CDC recommends the IIV annually for anyone over 6 months old: it is given intramuscularly and is available as a trivalent or quadrivalent (containing three or four strains of the influenza virus). Each brand has a recommended age range, including a couple trivalent IIVs specifically for adults over the age of 65. The RIV is a quadrivalent vaccine for adults over the age of 18 and is given intramuscularly. LAIV is a quadrivalent nasal spray approved for use between the ages of 2 and 49. The CDC also recommends two doses of influenza vaccine separated by at least four weeks for children between six months and eight years who did not receive at least two previous doses of influenza vaccine (their first flu season being vaccinated) (CDC, 2019a). The cost-effectiveness of influenza vaccination strategies was tested in an urban, tertiary, freestanding pediatric emergency department by Hart, Stevenson, Smith, La Joie & Cross (2018). Four different focuses were tested in this study: vaccinate all patients, no patients, patients under the age of 5 only, or patients under the age of 5 or high risk only. They found that vaccinating all of their patients was the most cost-effective strategy, with a cost of $103.69 per patient and 93 flu cases per 1000 patients, versus $129.26 per patient and 120 flu cases per 1000 patients when no one was vaccinated (Hart et al., 2018). The CDC recommends that all healthcare providers (HCPs) are vaccinated for influenza annually to help prevent the spread of the disease to our patients, coworkers, and families. Some hospitals have started requiring their employees to get vaccinated or provide proof of vaccination off-site. In a nationwide survey, the number of hospital systems surveyed requiring influenza vaccination increased from 37% in 2013 to 61% in 2017. Unfortunately, only 3 of 73 Veterans Affairs (VA) hospital systems required influenza vaccination amongst HCPs in 2017 (Greene et al., 2017).

The vaccine for measles, mumps, and rubella (MMR) is recommended by the CDC at 12-15 months and a booster dose at age four to six years (CDC, 2019a). Measles (Rubeola) is a viral rash with associated fever that can lead to blindness, encephalopathy, or even death. Mumps is a viral infection that presents with its characteristics swollen parotid glands as well as fever, headache, body aches and can lead to viral meningitis. Rubella is a viral infection that is mild in children but can be highly dangerous in pregnant women especially if contracted in the first trimester. Internationally, the measles vaccination is available in 167 countries with single-dose worldwide coverage of 85% and two-dose coverage of 67% worldwide (WHO, 2018b). Deaths related to measles have decreased by 84% from 550,000 in 2000 to 89,780 in 2016 (WHO, 2018c). The mumps vaccine is currently only available in 122 countries worldwide, while the Rubella vaccine is available in 162 countries with global coverage of 52% (WHO, 2018b).

The varicella vaccine (VAR) is recommended by the CDC to vaccinate against the chickenpox infection with a two-dose series at 12-15 months old and a booster at four to six years old. If given before the age of 12, the two doses must be given at least three months apart. Over the age of 13 the two doses should be spaced at least four weeks apart. It can also be given as a combination vaccine with the MMR called ProQuad (CDC, 2019a).

Hepatitis A (HepA) is recommended by the CDC as a two-dose series given after the age of 12 months and spaced at least six months apart. It is also recommended prior to international travel to endemic areas (CDC, 2019a).

Meningitis is an infection of the meninges surrounding the brain that can be viral, bacterial, or fungal. Bacterial meningitis can be caused by Neisseria mengitidis, or meningococcus. It can be very serious, with a 10-15% mortality rate even with optimal treatment. It can also lead to loss of limbs, deafness, or brain damage. There is increased risk of transmission in close living quarters, such as environments like dormitories and barracks as it is transmitted via saliva and other respiratory secretions. There are five main serogroups of meningococcus: A, B, C, W and Y. The conjugate vaccine (MenACWY) acts as a vaccine against four of those serotypes (Linder & Malani, 2019). It is recommended by the CDC for 11-12-year-olds with a booster recommended at age 16 or in younger children with significant immunocompromise. It is also required for admission to college in most states. The meningococcal B vaccine targets the B serotype and is a two-dose series recommended at the age of 16-18 based on clinical discretion regarding risk (CDC, 2019a).

The human papillomavirus (HPV) vaccine prevents many types of cancer, including cervical, oropharynx, anal, penile, vaginal, and vulvar cancer, as well as genital warts. The cost for eight million doses of the vaccine is estimated at $1.6 billion, while the estimated treatment cost for HPV-associated disease is $8 billion (Moreno, 2019). Per the CDC, the HPV vaccine is a two-dose series spaced at least five months apart recommended between the ages of 9 and 14. If over the age of 15, it is a three-dose series spaced at least four weeks apart for the first and second doses, and at least 12 weeks apart for the second and third doses, and at least 5 months spacing between the first and third doses (CDC, 2019a). Recommended initially in 2007, the coverage rates have not been as high as most other vaccines introduced in the U.S. One explanation for this has been a lack of state regulations requiring this vaccination for school entry (as of now, only Rhode Island requires it in all students, Virginia and DC require it in girls in the sixth grade or above). Schwartz & Easterling (2015) comment on how much faster the states required previous vaccinations for school entry, such as the varicella (50 states and DC), and hepatitis B vaccine (47 states and DC) which were introduced in the 1990’s, as well as the meningitis conjugate vaccine (29 states and DC) which was introduced in 2005. Another explanation is lack of understanding about what the vaccine does and why adolescents need it. Because HPV is transmitted sexually, parents are uncomfortable giving it to young teens, despite studies that have shown it does not increase sexual activity amongst teens. A short education program for parents lasting about 15 minutes and including a PowerPoint presentation was shown to increase parents knowledge about the vaccine, as well as increase the intent to vaccinate from 34 of 86 (40%) parents prior to the program to 60 of 86 (70%) after the program (Weinstein et al., 2016). The nationwide coverage was only 37.6% in 2013 for adolescent girls and 13.9% for adolescent boys (Schwartz & Easterling, 2015). This number had increased to 65% coverage for a single dose and 48.6% coverage for both doses nationwide in 2017 (Walker et al., 2018).


Figure 2: CDC Recommended Adult Immunization Schedule, United States, 2019

Many of the adult immunizations in Figure 2 (above) have already been discussed, with the exception of the Zoster vaccinations, which are exclusively for use in adults. Used to prevent shingles, there are two options for herpes zoster vaccinations. ZVL or Zostavax is a live vaccine approved as a single dose approved for age 60 or above. RZV, or Shingrix, is a recombinant vaccine approved as a two-dose series that should be given 2-6 months apart at the age of 50 or above (CDC, 2019a). ZVL has been available since 2006 and has been found to decrease the risk of shingles by about 50% and the risk of postherpetic neuralgia by 67%. Because it is a live vaccine it cannot be given to immunocompromised patients. RZV was approved for use in 2017. It reduces the risk of shingles or postherpetic neuralgia by 90% and is thus preferred by the CDC. It is also safe for immunocompromised patients (Jin, 2018).

Pregnancy and Vaccinations

            There are two vaccines that are often intentionally recommended for pregnant women, including the influenza vaccine and Tdap vaccine. A recent study looking at over 60,000 children born to women who had received the influenza vaccine during pregnancy found no increased risk of early childhood morbidity (up to the age of 4-5) (Hviid, Svanstrom, Molgaard-Nielsen & Lambach, 2017). Zerbo et al. (2017) looked at almost 200,000 children in northern California born between 2000 and 2010. Overall, they found no increased risk for autism spectrum disorders (ASD) in children born to mothers with influenza infections or who received the influenza vaccine during pregnancy. When the risk was broken down to trimester, only when the mother was vaccinated during the first trimester was there a slight increase in risk (Zerbo et al., 2017). Regarding efficacy, Madhi et al. found a 50% or better efficacy rate against influenza for up to six months after delivery when pregnant mothers with and without HIV were administered the trivalent IIV in South Africa. Since the recent recommendation change regarding Tdap vaccines during each pregnancy, a study by Sukumaran et al. (2015) sought to determine if repeat Tdap vaccinations within two years of each other increased risk for adverse effects. They found no increased risk of acute adverse effects (local reaction, etc.) or adverse birth outcome (preterm labor, small for gestational age, etc.) even in the subset of women who have received the vaccination within two years (Sukumaran et al., 2015). Other vaccinations, such as the HPV vaccine, may occur inadvertently when the woman is not yet aware that she is pregnant. A study in Denmark reviewed over 1,600 pregnancies that had been exposed to the HPV vaccine. They found no significantly increased rate in exposed versus unexposed pregnancies of major birth defects (3.9% versus 3.3%), spontaneous abortion (4.3% versus 7%), preterm delivery (6.5% versus 5.7%), low birth weight (4.3% versus 3.9%), small for gestational age (9.7% versus 11%) or stillbirth (.4% versus .2%) (Scheller, Pasternak, Molgaard-Nielsen, Svanstrom & Hviid, 2017). Voysey et al. (2017) found that a higher concentration of maternally-derived antibodies reduces an infant’s immune response to vaccination, but that this effect is reduced as the child ages.

Future Work Towards Worldwide Health Through Immunization

            There are diseases that are found more frequently outside of the U.S. and represent significant risk to worldwide health, such as dengue fever, malaria, and cholera. Dengue fever (or just dengue) is caused by the dengue virus. Up to 20% of the severe form of dengue is lethal. It is found in very rainy areas/seasons of Bangladesh and India mostly, but roughly 40% of the world is at risk with 390 million cases worldwide annually. It is a mosquito-borne illness. The vaccine developed for dengue by Sanofi is a live attenuated vaccine called CYD-TDV or Dengvaxia. It was released in 2015 and is approved currently in 20 endemic countries for people ages 9-45 only. While the vaccine is helpful, it is far from a perfect solution. While the vaccine helps improve immunity in patients with a prior history of dengue infection (seropositive), it increases the risk of severe dengue and hospitalizations in seronegative people. For that reason, people should be screened with an antibody titer or confirm a history of dengue prior to vaccination. For this reason, most prevention methods currently focus on preventing transmission via the mosquito Aedes aegypti (WHO, 2018a).

            Malaria is a parasitic infection transmitted by Anopheles mosquitoes. Worldwide, there were 219 million cases of malaria in 2017 with 435,000 associated deaths. RTS,S/AS01, or Mosquirix, is an injectable vaccine that provides partial protection in young children with pilots in scheduled for this year in Malawi, Kenya, and Ghana (WHO, 2019b). In 2015 the RTS,S phase III clinical trials were published. The vaccine was given to infants age 6-12 weeks as well as toddlers age 5-17 months. Group 1 received a series of three injections monthly plus a booster 18 months later. Group 2 received just the initial series of three injections monthly and an unrelated meningococcal conjugate booster 18 months later. Finally, the control group was given only rabies and meningococcal conjugate vaccines. All participants also received insecticide-treated bednets, a current mainstay in malaria prevention efforts worldwide. Within group 1 there were 6,616 episodes of malaria in children, 116 of which were severe, and 4,993 episodes of malaria in infants, 96 of which were severe. In group 2 there was 7,396 episodes of malaria in children, 169 were severe, and 5,444 episodes of malaria in infants, 104 of which were severe. Finally, the control group was found to have 9,585 episodes of malaria amongst children, 171 severe, and 6,170 episodes of malaria amongst infants, 116 were severe. In total, they saw 306 deaths secondary to malaria within the study. The only safety concern was about 40 cases of meningitis reported amongst vaccinated patients within 30 days of vaccination (RTS,S Clinical Trials Partnership, 2015). A later study looking at efficacy of RTS,S/AS01 at seven years found the vaccine was effective short term, but offered no protection in the fourth year following vaccination. Even worse, the vaccine produced a rebound effect in the fifth year causing an increase in malaria cases during that year amongst those patients with higher than average exposure compared to the control group (Olotu et al., 2016). The relatively poor performance of this vaccine has been attributed to the parasitic nature of its target, citing the complexity of parasitic vaccines as a huge difficulty. The cons of the vaccine include decreased efficacy in infants versus toddlers as well as a rapidly decreasing effectiveness after the first three years. This, in combination with safety concerns regarding meningitis as well as an increased mortality rate amongst vaccinated girls, has led many to call for increased prevention efforts via vector control and improved treatment facilities and protocols. In addition, work has begun on a possible transmission-blocking vaccine (instead of RTS,S which is a pre-erythrocytic vaccine). Despite all of this, the European Medicines Agency (EMA) recommended RTS,S for licensure among young children ages 6 weeks-17 months (Mahmoudi & Keshavarz, 2017).

            Cholera causes acute diarrhea, and 80% of cases can be treated effectively with oral rehydration. There are currently three oral vaccines available to prevent cholera. Dukoral is approved for use in children over the age of two, with three doses recommended in age two to five, or two doses recommended for adults or children over the age of five. This provides protection for a period of two years and can be used for people travelling to areas with higher risk of cholera. Shanchol and Euvichol-Plus are both approved for use in adults and children over the age of one year, consists of two doses, and provide protection for three years (WHO, 2019a). Results of practical use of Shanchol was tested recently in a group of patients in Bangladesh. A single dose of the vaccine was shown to have an efficacy rate of 40% against all cholera episodes and 63% against severe cholera episodes. It was most efficacious in children age 5-14 years old. A limitation of this study was its short follow-up, which was only 180 days (Qadri et al., 2016).

Vaccine Hesitancy and the Antivaxxer Movement

            The WHO listed vaccine hesitancy as one of the top ten threats to global health in 2019. They define vaccine hesitancy as reluctance or refusal to vaccinate despite availability of vaccines. According to the WHO, this hesitancy has led to a 30% increase in measles cases worldwide. This movement against vaccinating children has been dubbed the Antivaxxer Movement. The most common reasons cited for vaccine hesitancy include complacency, inconvenience in access, and lack of confidence in vaccine efficacy and safety (WHO, 2019c). A recent study on the public health and economic consequences of vaccine hesitancy predicted that a 5% decrease in MMR vaccine coverage in the U.S. would lead to three times the number of measles cases in this country between the ages of 2 and 11 yearly. This would correlate with over $2 million in public sector costs. These figures would not include costs and cases amongst infants, adolescents and adults. They cited the most common reasons to refuse or delay vaccination as misinformation related to safety and a reduced perceived risk of the disease itself (Lo & Hotez, 2017). Despite the fact that the U.S. achieved elimination of endemic measles in 2000, there have been several measles outbreaks in the last five years in the U.S. related to unvaccinated individuals. 383 cases were reported in and around an Amish community in Ohio in 2014. In 2014-15, an outbreak that began at Disneyland in California lead to 147 cases being reported. In 2017, 75 cases were reported in and around a Somali-American community in Minnesota. In 2018, there were 282 cases reported in and around an Othrodox Jewish community in New Jersey and New York. It can cost up to $142,000 to respond to a single case of measles. Measles is not only dangerous during the active infection, but also causes a post-infection immunosuppression that increases all-cause mortality for 2-3 years following the infection secondary to resetting of previously acquired immunity, a phenomenon known as immunological amnesia. Outbreaks also cause strain on our public health and healthcare system in general, diverting human and other resources away from other important ongoing projects (Sundaram, Guterman & Omer, 2019). In an attempt to increase vaccination rates, the state of California passed SB277 in 2016, eliminating the personal belief exemption (PBE). This meant that any children entering a public or private kindergarten in the fall of 2016 would have to be vaccinated or obtain a medical exemption (ME). PBEs decreased in the 2016-17 school year from 2.37% to 0.56% (due to grandfathering in some students already enrolled in multiyear transitional kindergarten programs), the lowest since 1996. To obtain an ME, a child must receive a note from their doctor which includes the medical reason why the child may not be vaccinated. There is slightly broader discretion to obtain an ME, which now includes family medical history as a potential reason. The number of MEs increased from 0.17% to 0.51% in the 2016-17 school year, but the total number of exemptions from both sources decreased from 2.54% to 1.06%, the lowest since 2000 (Delamater, Leslie & Yang, 2017). The CDC currently lists 314 cases of measles nationwide so far in 2019 (CDC, 2019b). The 2018-19 measles outbreak in Rockland County, New York currently lists 159 cases as of March 29, 2019 (Rockland County Department of Health, 2019). The New York City Department of Health (2019) has reported 214 cases of measles in Brooklyn and Queens since October. This outbreak started in and around an Orthodox Jewish community there after international travel to Israel. There have been 14 cases of measles reported thus far in Texas in 2019 (Texas Department of State Health Services, 2019). The state of Washington has declared a state of emergency because of an outbreak there, with 74 cases reported thus far (Washington State Department of Health, 2019). That outbreak has also spread to neighboring Oregon, with 10 total cases reported there, four of which have been directly linked to the outbreak in Washington’s Clark County (Oregon Health Authority, 2019).


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