Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians With morbidity and mortality from vaccine-preventable diseases [VPDs] having reached record lows, vaccines are one of the most successful tools for biomedical science and public health. Yet paradoxically, the effectiveness of vaccination has led to the reemergence of anti-vaccination sentiments. Vaccines may be seen unnecessary or dangerous because incidence rates of VPDs in developed countries have plummeted. Vaccine “reactions” – negative health events following vaccination, attributed to the vaccine – then appear to be more common than the diseases themselves. In this way, vaccines can be considered victims of their own success. 1 Immunization rates continue to be high but concerns about vaccine safety are increasing. Current communication methods do not appear to lead to more comfort with vaccines, making it more important than ever that state and territorial public health agencies, charged with promoting, monitoring and tracking vaccine use, understand the growing reluctance among parents and guardians to fully vaccinate their children and identify effective messages about the benefits of vaccines. In August 2009, ASTHO commissioned a survey of 1,278 U.S. parents and guardians to gather information about effective messages and materials for addressing parental concerns, support more informed decisions on the part of parents and guardians, and how best to clearly and accurately promote the benefits of vaccines in ways that resonate with family decision makers. The study was designed to explore: • • • The reasons parents and guardians have for not vaccinating their children The most effective messages for addressing this resistance Information sources about vaccines that are the most trusted and influential. An additional objective was to understand the characteristics that distinguish parents who vaccinate from those who refuse, including their demographics, attitudes and beliefs, and responsiveness to messages for and against childhood vaccinations. This paper is a summary of the findings from the ASTHO study. Methods During a two week period in August 2009, interviews were conducted online using an established survey panel. Interviews averaged 25 minutes in duration. To qualify for the survey, respondents had to live in the United States with a child under the age of 18, and be responsible for decisions about the health care the child receives. The sample was weighted to be demographically representative of the U.S. population of households with children under 18 years with respect to geography, age of the respondent, presence of children under 6 years, race and ethnicity, household income, and child’s health insurance status. To better understand differences between parents who vaccinate and those who refuse, the study included both groups. Refusers were divided into two groups: SIGNIFICANT REFUSERS, who have refused any of Diphtheria-Tetanus-Pertussis (DTaP), Haemophilus Influenza type B (Hib), Hepatitis B, Meningococcal, Measles-Mumps-Rubella (MMR), Pneumococcal, Polio, Rotavirus, or Varicella vaccines; and MINOR REFUSERS who have refused any of Hepatitis A, Human Papillomavirus (HPV) or Influenza vaccines. Vaccines for the MINOR REFUSERS category were chosen because most states do not have school entry requirements for these vaccines, allowing parents to elect to not vaccinate their children without encountering substantial obstacles. Vaccines in the SIGNIFICANT REFUSERS category are required for school entry in most or all states, thus requiring parents to take extra steps to obtain an exemption. © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 1 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians Respondents whose children had received at least one vaccine were further grouped according to: • Major concerns, including those who self-identified as being “very uncomfortable/unconfident” or “not comfortable/confident” about children receiving vaccinations • Minor concerns, including those who self-identified as being “comfortable/confident” about children receiving vaccinations • No concerns, including those who self-identified as being “very comfortable/confident” about children receiving vaccinations Respondents were blinded as to which category they were grouped into; determinations were made by the survey tool based on their responses to which vaccines they refused and, if their child had received all vaccines, their level of comfort with vaccinating. The majority of the parents surveyed were vaccinators with minor or no concerns (their children had received all of the recommended vaccines), however, in order to drill down to the issues of parents and guardians who had refused vaccines, additional interviews with SIGNIFICANT and MINOR REFUSERS were conducted. To adjust for this over- and under-sampling, the data was weighted so that the total reflected the actual U.S. population as determined by the survey. See Figure 1 below. Figure 1. Survey sample and actual U.S. population. Survey Sample Actual Population Vaccinators with No Concerns 19% 28% Significant Refusers Vaccinators with No Concerns 36% 43% Minor Refusers 24% 13% 16% Vaccinators with Major Concerns Vaccinators with Minor Concerns © 2010 Association of State and Territorial Health Officials 202-371-9090 5% 6% 10% Significant Refusers Minor Refusers Vaccinators with Major Concerns Vaccinators with Minor Concerns 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 2 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians Regardless of the vaccination status of the child in their care, all respondents answered all following survey questions, including questions about vaccine exemptions; whether and why vaccines may have been delayed (if not refused); attitudes about government, vaccine requirements, and vaccine risks and benefits; messages about vaccines; messengers for vaccine-related messages; and sources of vaccine information. Results Refusing and Delaying Vaccines Of those surveyed, 47% reported being very comfortable/confident with their children receiving vaccinations, 43% were comfortable/confident, while 8% were not comfortable/confident, and 2% were very uncomfortable. Interestingly, the majority of both SIGNIFICANT REFUSERS and MINOR REFUSERS said they were very comfortable (25% for both groups) or comfortable (38% and 46% respectively) about their children receiving vaccinations, although the percentages are lower than among VACCINATORS WITH NO CONCERNS. Among all respondents, 16% have refused a vaccine. Of these, 6% are MINOR REFUSERS (who refused only HepA, HPV or Flu) and 10% are SIGNIFICANT REFUSERS. Influenza and HPV being the most commonly refused (8% each), followed by Varicella (5%) and other vaccines at 2-3%. Additionally, 13% have delayed a vaccine, with DTaP being the most commonly delayed (4% of respondents) and other vaccines at 2-3%. People who refused Hib or Polio vaccines were mostly likely to refuse other vaccines as well, while those who refused HPV or influenza refused the fewest other vaccines. The most common reason across all categories of respondents for delaying or refusing vaccines was concern about too many vaccines being given at the same time. Additional reasons for delaying vaccines are found in Figure 2. Figure 2. Reasons for Delaying or Refusing Vaccines. Stated reasons for delaying or refusing vaccines Total Significant Refuser Minor Refuser Vax-Major Concern VaxMinor Concern Vax-No Concern Unweighted Base (278) (130) (57) (47) (31) (13) 53% 59% 66% 51% 51% 35% 12 14 6 12 15 8 Child was sick 9 8 2 23 11 5 Family/friend recommended delaying 5 7 3 12 4 0 Other (Grand Net) 33 32 35 30 30 37 Insurance Concerns (Net) 3 0 2 1 3 10 Had no insurance 2 0 1 1 0 10 % Selecting Each Reason Did not want too many vaccines given at same time Doctor recommended delaying the vaccine © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 3 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians Stated reasons for delaying or refusing vaccines Total Significant Refuser Minor Refuser Vax-Major Concern VaxMinor Concern Vax-No Concern Not covered by our insurance 1 0 1 0 3 0 Safety Concerns (Net) 9 9 18 10 10 0 Concerned about side effects 4 3 3 0 10 0 Risk of autism 2 3 2 4 0 0 Too new 1 0 5 0 0 0 Other safety concerns 3 4 8 8 0 0 Unnecessary (Net) 4 4 6 9 2 0 Wait for child to acquire it naturally 2 2 1 7 0 0 Didn’t think it was necessary 2 1 5 1 2 0 My own research/ research myself 4 5 2 2 0 8 Waiting for the child to be older 3 3 5 0 4 0 Not comfortable with it 2 5 3 0 2 0 Miscellaneous Profiles of Respondents Demographic Profile Overall, we found few significant demographic differences across the categories. The SIGNIFICANT REFUSERS tend to be better educated, and have slightly higher household incomes than other groups. MINOR REFUSERS tend to have older, rather than younger children, which we suggest may be related to refusal of HPV vaccine, though we did not ask this question. VACCINATORS WITH MAJOR CONCERNS include a higher percentage of African-Americans, a lower percentage of Whites, and are less likely to be employed. Conversely, VACCINATORS WITH MINOR CONCERNS include a lower percentage of AfricanAmericans and Hispanics, and a higher percentage of Whites. Geographic Profile We found considerable geographic differences in the distribution of the categories. There are more SIGNIFICANT REFUSERS in the Pacific states (14%) (CA, OR, WA). There are fewer SIGNIFICANT REFUSERS and more VACCINATORS WITH MINOR CONCERNS in East South Central states (4% and 51%) (KY, TN, MS, AL) and West North Central states (5% and 46%)(ND, SD, NE, KS, MN, IA, MO). There are the most VACCINATORS WITH NO CONCERNS in South Atlantic states (50%)(DE, MD, DC, WV, VA, NC, SC, GA, FL) and West South Central states (51%)(TX, OK, AR, LA). Attitudinal Profile We asked various questions to get a sense of attitudes about government, immunization requirements, and vaccine risks and benefits. In general, respondents had a positive view about the role of public health and tended to agree that protecting and improving public health is an important job of the government. Generally, parents are not well informed about vaccination requirements and exemption © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 4 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians options. Only 27% of VACCINATORS WITH MAJOR CONCERNS and 28% of VACCINATORS WITH MINOR CONCERNS felt well informed about the exemptions available in their state. By contrast, 52% of SIGNIFICANT REFUSERS felt well informed about the exemptions. Opinions about vaccine requirements vary by category. VACCINATORS WITH MINOR or NO CONCERNS tend to disagree that vaccinations should only be required against the most dangerous diseases, and do not have concerns about state vaccination requirements. In contrast, VACCINATORS WITH MAJOR CONCERNS, MINOR CONCERNS and SIGNIFICANT REFUSERS agree that children should only be required to get vaccinations against the most dangerous diseases, and disagree that the government’s immunization requirements for children are flexible. VACCINATORS WITH MAJOR CONCERNS are the most concerned about vaccine safety and the most likely to feel government does not take vaccine safety concerns seriously enough. Across all categories of respondents, the most concerning side effects are seizures, encephalopathy, Guillian-Barre Syndrome, blood clots and intussusception. Least concerning side effects include swollen/sore arm or leg, fever under 101, headache, drowsiness, or skin reaction. Vaccine Administration Location The majority of the children in this survey received their health care and vaccinations at a doctor’s office, and over 90% receive the majority of their vaccinations at the same place they get most of their health care. However, SIGNIFICANT REFUSERS are the most likely to use different venues for vaccinations versus other health care, and they, along with VACCINATORS WITH MAJOR CONCERNS, are less likely to receive care or vaccinations at doctor’s offices, compared to the other groups. Reasons for Opposing Vaccinations Concern about Vaccine Safety and Side Effects: The survey included an open-ended question asking, “In your own words, please describe the biggest reasons why you, yourself, might oppose vaccinations for your child or prefer not to have your child vaccinated”. The most common response was concern about vaccine safety and side effects. VACCINATORS WITH MAJOR CONCERNS and those with MINOR CONCERNS are both more likely than REFUSERS to mention safety concerns, while those with NO CONCERNS are least likely to do so. Almost one-fifth of VACCINATORS WITH MAJOR CONCERNS specifically mention concern about autism, whereas only 5% of parents, overall, mentioned autismrelated concerns. VACCINATORS WITH MAJOR CONCERNS are also the most likely to mention concerns about giving too many vaccines at the same time. Lack of Necessity or Trust: SIGNIFICANT REFUSERS were more likely than others to mention that not all vaccines are necessary – that some diseases are not serious enough to warrant a vaccine, that they reduce the body’s natural immunity, or they do not trust the vaccines. MINOR REFUSERS are more likely than others to mention lack of trust (in vaccines and the government), as well as opposition to HPV in particular. About one-quarter of parents said they do not oppose vaccinations, and over one-third did not volunteer any reasons not to vaccinate. Reasons for Supporting Vaccinations Protecting Their Child’s Health: An open-ended question was posed to parents about why they support vaccinations for their child, to which the most common reason is to protect their child’s health. SIGNIFICANT REFUSERS and VACCINATORS WITH MAJOR CONCERS are less likely to mention this than © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 5 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians are the other groups; however, it is mentioned by at least 60% of each of these groups. (SIGNIFICANT REFUSERS – 63%, MINOR REFUSERS – 66%, VACCINATORS WITH MAJOR CONCERNS – 60%, VACCINATORS WITH MINOR CONCERNS – 76%, VACCINATORS WITH NO CONCERNS – 72%). Preventing the Spread of Disease: The next most commonly mentioned reason is to prevent the spread of disease. MINOR REFUSERS are more likely than other parents to mention this, while SIGNIFICANT REFUSERS and VACCINATORS WITH MAJOR CONCERNS are again less likely to mention it. About 10% of parents mention that vaccines are required by the government or recommended by their doctors. VACCINATORS WITH MAJOR CONCERNS are particularly likely to mention requirements for school admission. Messages Negative Messages The respondents were given a list of negative messages about vaccines and asked to rate whether they had previously heard it, and whether each was believable and convincing. The negative messages tested that were ranked as the most believable and the most convincing all have to do with risks of adverse effects. The messages were: • • • • Vaccines can cause serious health problems, like auto-immune disorders, asthma or autism. Vaccines are unsafe due to ingredients such as thimerosal or aluminum. Too many vaccines given too soon can harm children. Combination vaccines are more likely to cause adverse reactions. There was little difference across categories in their ratings of the negative messages, or in their ranking of the most convincing arguments. See Figure 3. Positive Messages Generally, positive messages about vaccination are rated as much more convincing and much more believable than the negative messages, as well as more familiar. The most compelling positive message (also the most believable and the most familiar) is that “Vaccination is one of the most important ways I can protect my child.” The least compelling positive message (also the least believable and the least familiar) is that “Scientific studies do not support the concern that thimerosal causes autism.” There was little difference across categories in the ratings of the positive arguments, or the ranking of the most convincing arguments. See Figure 4. © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 6 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians Figure 3. Negative Messages about Vaccinations. © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 7 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians Figure 4. Positive Messages about Vaccinations. Influencers In an effort to better understand what most influences a parent’s decision on vaccines, participants were asked to identify the sources of influence. Parents typically give themselves over half of the “votes”, and their spouses about a quarter of the votes, as to whether their child receives vaccines. The other major influence is the pediatrician, who has less influence than the parents. SIGNIFICANT REFUSERS give slightly less influence to pediatricians, while VACCINATORS WITH MAJOR CONCERNS give slightly more influence to pediatricians, and slightly less influence to themselves. Pediatricians and spouses are generally the most used and influential sources. Nurses and CDC are additional sources and are influential among VACCINATORS WITH MINOR or NO CONCERNS, but are less so among the other groups. Websites are commonly used by all segments except VACCINATORS WITH NO CONCERNS, but are not very influential. © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 8 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians Figure 5. Information Sources about Vaccinating Children. Significant Refusers Used & Influential Vax-Major Concerns Vax-Minor Concerns Vax-No Concerns Pediatrician Spouse Pediatrician Spouse Pediatrician Spouse Nurse CDC Pediatrician Nurse Public Health Officials CDC Websites Public Health Officials CDC School Officials Other family Nurse Websites Grandparents Parenting experts Grandparents Non-government health orgs Public health officials Minor Refusers Pediatrician Spouse Used, but Not Influential Websites Nurse CDC Websites Nurse Public Health Officials Influential, but not used Expert in alternative medicine Books CDC Blogs/on-line forums Grandparents TV/Radio Programs Participants were asked, “of the convincing reasons for vaccinating your child, what is the most convincing source of the messages?” Responses indicated that pediatricians are by far the most convincing source of positive messages about vaccination, followed by the CDC and Public Health Officials. Figure 6. Most Convincing Positive Message Sources. (% selecting as “most convincing source”) Protect Child (n=448) Disease still a threat (n=217) Most Influential Pediatrician (87%) Moderately Influential CDC (26%) Pediatrician (52%) CDC (39%) Public Health Officials(23%) Somewhat Influential Public Health Officials (13%) Non-Govt Health Orgs (14%) Prevent Disease Episodes (n=163) Pediatrician (66%) CDC (40%) Public Health Off (21%) Non-Gov Health Orgs (13%) Wipe out Diseases (n=150) Pediatrician (65%) CDC (36%) Public Health Off (16%) Websites (11%) Non-Gov Health Orgs (10%) Social Obligation (n=123) Pediatrician (70%) CDC (26%) Public Health Off (21%) Spouse (14%) Studies Show Vaccines are Safe (n=119) Pediatrician (71%) CDC (42%) Public Health Off (32%) Non-Gov Health Orgs (14%) Expert in alternative medicine (12%) Parents generally believe their pediatricians support vaccinations. However, they are less likely to believe that their pediatricians are well-informed about childhood vaccinations or spend sufficient time with them explaining risks and benefits of vaccinations. Additionally, 53% of VACCINATORS WITH MAJOR CONCERNS felt that their child’s doctor did not take enough time to explain the risks and benefits of vaccinations. © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 9 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians Discussion The results of this survey support other findings in that the majority of parents continue to fully vaccinate their children and are comfortable with the benefits of vaccines. This study found that 90% of the respondents were either very comfortable or comfortable with their children receiving vaccinations. A study conducted in 2005 found 84% of parents agreed or strongly agreed that vaccines are necessary. 2 A study in 2000 found 87% deemed immunization an extremely important action that parents can take to keep their children well. 3 This research is also consistent with other studies, however, that have found that parents continue to have concerns about vaccine safety. The most common reason given by parents not to vaccinate was the risk of adverse effects. Misconceptions about immunizations continue. For example, concerns about thimerosal continue to be high and messages that scientific studies do not support the concern are the least convincing and least believable of the messages tested. These findings indicate that factors other than current scientific facts contribute to the decision making process. …more consideration must be given to the social discourses underlying anti-vaccinationismreasons for refusing vaccines may involve alternative understandings of health, different perspectives on parental responsibility, or questioning the legitimacy of traditional authorities. These discourses exemplify postmodern tensions in society, making the anti-vaccination issue one of significant complexity. 4 All parents, except VACCINATORS WITH NO CONCERNS, were concerned by messages such as, “vaccines can cause serious health problems like auto-immune disorders, asthma or autism” and “too many vaccines given too soon can harm children.” The challenge for public health is how to effectively address these underlying concerns so that they do not lead to more parents delaying or refusing vaccines. Positive messages were generally rated as more convincing and more believable than negative messages. For instance: “Vaccination is one of the most important ways you can protect your child from lifethreatening illness and it’s the best-known protection against a number of infectious diseases.” A telephone survey in 2000 found that between 19% and 25% of parents surveyed have misconceptions about immunizations. 5 A recent study entitled, “Parental Vaccine Safety Concerns in 2009” found that over half of their respondents expressed concerns regarding serious adverse effects. 6 The ASTHO research found 16% of respondents refused a vaccine, while 13% have delayed a vaccine. The refusal rate is higher compared to previous studies, such as a 2009 study by Freed et al., which found an 11% refusal rate. Our study is the first recent study to include influenza vaccine, which may have contributed to the higher refusal rate in our study. If a parent refused the influenza vaccine one year for their child, it was recorded as refusing a vaccine. The study also found that positive messages were generally rated as more convincing and more believable than negative messages. The positive message that resonated with the SIGNIFICANT AND MINOR REFUSERS, and with VACCINATORS WITH MINOR OR NO CONCERNS was that “vaccination is one of the most important ways I can protect my child from life-threatening illness and it’s the best-known protection against a number of infectious diseases.” It may seem effective to confront negative messages about vaccines with negative messages about, for example, the consequences about not © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 10 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians vaccinating, but such messages did not test well in our study, and caution may be warranted in using this approach. Demographic information about vaccine refusers and vaccine concerns is essentially consistent with past work, with one variation. The basic finding is that there are few significant demographic differences across parent groups. In contrast to a 2005 study on immunization attitudes and beliefs, this survey found that SIGNIFICANT REFUSERS tend to be better educated and have slightly higher household incomes than the other groups. The The study found that 2005 study found that parents in the category labeled “fully VACCINATORS WITH MAJOR vaccinated with concerns” tended to have college degrees, higher CONCERNS were less likely to income, and private medical care. 7 Comparing these two findings have private health may indicate that college educated, higher income groups have insurance and less likely to moved from vaccinating their children despite concerns, to now receive care or vaccinations refusing vaccines. at a doctor’s office. Another interesting, though perhaps not surprising, finding is that VACCINATORS WITH MAJOR CONCERNS are less likely to have private health insurance and less likely to receive care or vaccinations at a doctor’s office. The above mentioned 2005 study also found that not having a regular doctor resulted in delayed immunizations. 8 Finally, this study found that the most influential source of information about vaccinations, aside from parents, is pediatricians. This is consistent with other findings. In the report on “Do Parents Understand Immunizations?” the authors state, Because health care providers are perceived by parents to be the most important source of information about communications – they have an opportunity and obligation to educate parents and correct misconceptions. 9 As was pointed out above, 53% of VACCINATORS WITH MAJOR CONCERNS felt that their child’s doctor did not take enough time to explain the risks and benefits of vaccinations. CDC and professional organizations are looking into ways to facilitate these communications. Conclusion The results of this survey bolster the notion that a strong majority of parents support vaccinations, but continue to have concerns about their safety and the potential for adverse effects. The fear of disease is not as prevalent as it was in the past, so convincing parents that vaccines continue to be necessary is an ongoing challenge. While immunization rates continue to be high, concerns about vaccine safety are increasing. Current communication methods based on scientific research do not appear to lead to more comfort with vaccines. The results of this survey suggest that pediatricians, public health officials and the Centers for Disease Control and Prevention are seen as reliable sources of information on vaccine issues. With a better understanding of which messages resonate with the public about the benefits of vaccines, public health officials can tailor their communications in a way to address the concerns of parents along the spectrum. If public health officials and providers can succeed in communicating the benefits of vaccines, then the country can continue to maintain high rates of coverage and avoid unnecessary loss of life due to © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 11 Communicating Effectively About Vaccines Summary of a Survey of U.S. Parents and Guardians vaccine preventable diseases. As stated by Freed and colleagues, Although information is available to address many vaccine safety concerns, such information is not reaching parents in an effective or convincing manner. Public health officials should construct and redesign vaccine information programs to address current safety concerns in a manner that is more targeted and tailored to specific subgroups of parents. 10 1 Kata, Anna. A postmodern Pandora’s box: Anti-vaccination misinformation on the Internet. Vaccine 28 (2010) 1709-1716. 2 Gust et al. American Journal of Health Behavior, 2005; 29(1):81-92. Immunization Attitudes and Beliefs Among Parents: Beyond a Dichotomous Perspective. P. 89. 3 Gellin, Bruce, et al. Do Parents Understand Immunizations? A National Telephone Survey. Pediatrics, Volume 106, Number 5, November 2000. p- 1097. 4 Kata, page 1715. 5 Gellin et al, 6 Freed, Gary et al. Parental Vaccine Safety Concerns in 2009. Pediatrics, Volume 125, Number 4, April 2010. 7 Gust et al. 8 Gust et al. 9 Gellin et al, pg 1101. 10 Freed, et al. P 658. © 2010 Association of State and Territorial Health Officials 202-371-9090 2231 Crystal Drive, Ste 450, Arlington, VA www.ASTHO.org 12
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