Effective Messages in Vaccine Promotion. A Randomized Trial

Transcription

1 : A Randomized Trial Brendan Nyhan Dartmouth College Jason Reifler University of Exeter Sean Richey Georgia State University Gary L. Freed University of Michigan Pediatrics (2014)

2 Vaccines: The threat of another UK Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children A J Wakefield, S H Murch, A Anthony, J Linnell, D M Casson, M Malik, M Berelowitz, A P Dhillon, M A Thomson, P Harvey, A Valentine, S E Davies, J A Walker-Smith 50,000 MMR vaccinations so far in battle to halt Welsh measles epidemic But up-take remains too low among the worst-hit 10 to 18 age group Antony Stone Thursday, 16 May 2013

3 US: The threat of MMR selective non-receipt MMR vaccination rates over 90% target but... Many states close to threshold High nonmedical exemption rates in some states Concerns about clustering leading to outbreaks Record post-elimination outbreaks this year

4 US: The threat of MMR selective non-receipt TABLE 2 Parental Perspectives on Vaccines Perspective % That Strongly Agreed or Agreed With Statement Getting vaccines is a good way to protect my child(ren) from disease. 90 Generally I do what my doctor recommends about vaccines for my child(ren). 88 I am concerned about serious adverse effects of vaccines. 54 New vaccines are recommended only if they are as safe as older vaccines. 51 Parents should have the right to refuse vaccines that are required for school 31 for any reason. Some vaccines cause autism in healthy children. 25 My child(ren) does(do) not need vaccines for diseases that are not common 11 anymore. (Freed et al. 2010)

5 Theoretical approach Motivated reasoning: Disconfirmation bias (Nyhan and Reifler 2010) Implication: Corrections can fail or backfire Loss frames: Prospect theory: Loss frames more effective for behaviors seen as risky (Bartels, Kelly, and Rothman 2010) Risk: Fear appeals that are too strong may backfire (though see Witte and Allen 2000) and graphic messages can produce reactance (e.g., Erceg-Hurn and Steed 2011)

6 Experimental conditions Each treatment adapted from public health materials: Correction of vaccine misinformation (CDC) Disease danger: Text (VIS) Disease danger: Images (IL DPH) Disease danger: Narrative (CDC) Control group

7 Correction of vaccine misinformation All children should be vaccinated for measles, mumps, and rubella. The measles, mumps, and rubella vaccine (MMR) is safe and effective. Because signs of autism may appear around the same time children receive the MMR vaccine, some parents may worry that the vaccine causes autism. Vaccine safety experts, including experts at the Centers for Disease Control (CDC) and the American Academy of Pediatrics, agree that MMR vaccine is not responsible for recent increases in the number of children with autism. A 2004 Institute of Medicine report concluded that there is no link between autism and MMR vaccine, and that there is no link between autism and vaccines that contain thimerosal as a preservative. Many scientific studies have found no link between MMR vaccine and autism. These studies include: A September 2008 published in Public Library of Science was conducted to determine whether results from an earlier study claiming to find measles virus RNA in the intestinal tissue of autistic children could be confirmed. The results could not be confirmed, and no link between MMR and autism was found. A 2006 study published in the Journal of Autism and Developmental Disorders of 351 children with autism and 31 typically-developing children did not find a link between MMR vaccination and autism. A 2002 study by CDC in the New England Journal of Medicine followed more than 500,000 children and found no association between MMR vaccination and autism.

8 Disease danger: Text All children should be vaccinated for measles, mumps, and rubella. These are serious diseases. Measles Measles virus causes rash, cough, runny nose, eye irritation, and fever. It can lead to ear infection, pneumonia, seizures (jerking and staring), brain damage, and death. Mumps Mumps virus causes fever, headache, and swollen glands. It can lead to deafness, meningitis (infection of the brain and spinal cord covering), painful swelling of the testicles or ovaries, and, rarely, death.

9 Disease danger: Text (cont.) Rubella (German Measles) Rubella virus causes rash, mild fever, and arthritis (mostly in women). If a woman gets rubella while she is pregnant, she could have a miscarriage or her baby could be born with serious birth defects. You or your child could catch these diseases by being around someone who has them. They spread from person to person through the air. Measles, mumps, and rubella (MMR) vaccine can prevent these diseases. Most children who get their MMR shots will not get these diseases. Many more children would get them if we stopped vaccinating.

10 Disease danger: Images All children should be vaccinated for measles, mumps, and rubella. These are serious diseases. Because of advances in public health, most people in the United States have never had measles, mumps, and rubella or seen a child with these diseases. Please look at these pictures of children with the diseases before proceeding. Measles Mumps Rubella Rubella [SHOW IF DOV_STORY=5] Please examine the following information about bird feeding carefully. Q: What are the costs and benefits of bird feeding? A: It is difficult to assess the costs and benefits of bird feeding because it is difficult to compare the health of birds without access to feeders with birds that frequent feeders. Only one study was able to obtain some sound results. That study found that any benefits of feeding only appear to occur sporadically under extreme climactic conditions. No research has been able to demonstrate a cost. Aside from costs and benefits to birds, there is a cost and benefit to humanity. The costs are obvious--the expense of bird feeding supplies.

11 Disease danger: Narrative All children should be vaccinated for measles, mumps, and rubella. This is a true story that shows why vaccination is so important. If you hear 106 degrees you probably think heat wave, not a baby s temperature. But for Megan Campbell s 10-month-old son, a life-threatening bout of measles caused fevers spiking to 106 degrees and sent him to the hospital.

12 Disease danger: Narrative (cont.) We spent 3 days in the hospital fearing we might lose our baby boy, Campbell said. He couldn t drink or eat, so he was on an IV, and for a while he seemed to be wasting away. When he could drink again, we got to take him home. But the doctors told us to expect the disease to continue to run its course, including high fever which spiked as high as 106 degrees. We spent a week waking at all hours and soothing him with damp washcloths. Thankfully, the baby recovered fully. Megan now knows that her son was exposed to measles when another mother brought her ill son into their pediatrician s waiting room.

13 Study design/sample Two-wave Knowledge Networks survey experiment (with control group): Wave 1: Parents of children ages 17 and younger (n=2,299, June 2011) Measure vaccine attitudes (pre-treatment) Wave 2: Parents of children ages 17 and younger (n=1,759, June-July 2011) Experimental manipulation Measure vaccine attitudes (post-treatment)

14 Can we correct health misinformation? TABLE 2 Effects of Interventions on MMR Misperceptions Vaccines Cause Autism MMR Side Effects Autism correction 0.55* ( ) 0.81 ( ) Disease risks 1.15 ( ) 0.93 ( ) Disease narrative 1.35 ( ) 1.92* ( ) Disease images 1.47* ( ) 1.18 ( ) Somewhat favorable toward vaccines (baseline: least favorable) 0.22* ( ) 0.49* ( ) Most favorable toward vaccines (baseline: least favorable) 0.06* ( ) 0.23* ( ) N Ordered logit models with coefficients expressed as aors and 95% confidence intervals in parentheses (cutpoints omitted; *P, 0.05). Vaccines cause autism measures agreement on a 5-point scale from Strongly disagree (1) to Strongly agree (5) to the statement Some vaccines cause autism in healthy children. MMR side effects measures responses on a 6-point scale from Very unlikely (1) to Very likely (6) to the question Just based on what you know, how likely is it that children who get the measles, mumps, and rubella vaccine, which is known as the MMR vaccine, will suffer serious side effects? The experimental interventions are provided in the Supplemental Information. to vaccinate future children ( MMR next child ). The model in the left column of they would be less likely to vaccinate future children (aor = 0.52; 95% CI,

15 Can we correct health misinformation? 20% Vaccines cause autism: Strongly agree 20% MMR side effects: Very likely 15% 15% 10% 10% 5% 5% 0% Control Correction Risks Narrative Images 0% Control Correction Risks Narrative Images

16 Can we correct health misinformation? TABLE 3 Effects of Interventions on MMR Intention All Vaccine Attitudes Least Favorable Somewhat Favorable Most Favorable Autism correction 0.52* ( ) 0.36* ( ) 1.12 ( ) 2.98 ( ) Disease risks 0.98 ( ) 0.96 ( ) 1.23 ( ) 0.82 ( ) Disease narrative 1.09 ( ) 0.87 ( ) 2.26 ( ) 7.29 ( ) Disease images 1.29 ( ) 1.20 ( ) 2.00 ( ) 0.86 ( ) Somewhat favorable toward vaccines (baseline: least favorable) 7.61* ( ) Most favorable toward vaccines (baseline: least favorable) 16.19* ( ) N Ordered logit models with coefficients expressed as aors and 95% confidence intervals in parentheses (cutpoints omitted; *P, 0.05). MMR intention measures responses on a 6-point scale from Very unlikely (1) to Very likely (6) to the question If you had another child, how likely is it that you would give that child the measles, mumps, and rubella vaccine, which is known as the MMR vaccine? Indicators for vaccine attitudes groups (least, somewhat, and most favorable) are based on a tercile split of responses to the vaccine attitudes scale from Freed et al, 11 which was administered in a previous wave of the study. The experimental interventions are provided in the Supplemental Information. DISCUSSION We find that pro-vaccine messages do not always work as intended and that the effectiveness of those messages may vary depending on parental attitudes toward vaccines. Unlike several other studies of resistance to scientific evidence, corrective information that is broadly consistent with the literature on motivated reasoning about politics and vaccines In addition, our data provide little evidence that messages emphasizing the risks of vaccine-preventable diseases were effective in promoting vaccination intent. This finding is consistent with previous creased intent to vaccinate among parents who are the least favorable toward vaccines (those with more favorable attitudes were extremely likely to intend to vaccinate, reducing the scope for a positive effect). As with any study, these results have limitations that are worth noting. First,

17 Can we correct health misinformation? Very likely to give MMR to another child 100% Least favorable toward vaccines 100% Somewhat favorable toward vaccines 100% Most favorable toward vaccines 80% 80% 80% 60% 60% 60% 40% 40% 40% 20% 20% 20% 0% Control Correction Risks Narrative Images 0% Control Correction Risks Narrative Images 0% Control Correction Risks Narrative Images

18 Can we correct health misinformation? Very like 100% Least favorable toward vaccines 100% S 80% 80% 60% 60% 40% 40% 20% 20% 0% Control Correction Risks Narrative Images 0% Control

19 Conclusions Pro-vaccine messages can make vaccine backlash worse Corrective information may backfire, reduce vaccination intention Trying to scare parents can also be counterproductive Messaging should be tested experimentally

20 Sample demographics TABLE 1 Sample Demographics Wave 1 Wave 2 Wave 2 by Experimental Condition Disease Risks Autism Correction Narrative Danger Disease Images Control Sex, % Female Male Race/ethnicity, % White Black Hispanic Other Multiracial Education, % Not a high school graduate High school graduate Some college College graduate Household income, % Less than $ $ $ $ $ $ Age, % Younger than 30 y y y and older Region, % Northeast Midwest South West Number of children in household, % ,1,1,1,1 1,1 7+,1,1 Refused, %,1 N Sample statistics are computed by using weights calculated by Knowledge Networks41; weights are calculated separately for each wave so that the sample reflects the population of parents of children age 0 to 17 y from the Knowledge Networks panel. Due to rounding, some percentages may not add to 100%. The number of children in household was only asked in wave 1; the proportions listed for wave 2 reflect answers from wave 1 among those who completed both waves of the survey. Pearson s x 2 is non-significant for differences across intervention groups after a Bonferroni correction for multiple comparisons. the risk interventions had equal effects (F(2, 1744) = 7.98, P,.01). Likewise, whereas Disease images did not have a significant effect on MMR side effects, it did increase beliefs that vaccines cause autism (aor, 1.47; 95% CI, ), although the effect was not distinct from the other risk interventions (F(2, 1734) = 0.96, not significant). We could not reject the null hypothesis that intervention effects do not vary by vaccine attitude group for any intervention on Vaccines cause autism or MMR side effects. We thus do not estimate the effects of the treatments separately byvaccine attitudegroup in Table 2. We also could not reject the null hypothesisthat theeffects of the3 risk interventions were jointly 0 for Vaccines cause autism. However, we found that they were jointly significant for MMR side effects owing to the Disease narrative effect described above (F(3, 1743) = 6.17, P,.01). (In addition to these results, pre-specified interactions between the interventions and measures of trust in health professions and institutions were not consistently significant.) Figure 1 summarizes the effects of the interventions on vaccine misperceptions for a respondent in the least favorable vaccine attitude group using predicted probabilities from Table 2. Autism correction is most effective in reducing agreement with the autism misperception. Strong agreement declines from a predicted probability of 8.9% to 5.1% (and likewise for other response options). By contrast, the pre-

21 Control group Q: What are the costs and benefits of bird feeding? A: It is difficult to assess the costs and benefits of bird feeding because it is difficult to compare the health of birds without access to feeders with birds that frequent feeders. Only one study was able to obtain some sound results. That study found that any benefits of feeding only appear to occur sporadically under extreme climactic conditions. No research has been able to demonstrate a cost. Aside from costs and benefits to birds, there is a cost and benefit to humanity. The costs are obvious the expense of bird feeding supplies.

22 Control group (cont.) The benefits include learning more about birds and the joy of connecting with the natural world. Bird feeding provides a direct, intimate view of the natural world for more than 50 million Americans who feed the birds in their yards. It is most popular in winter, when birds seem to need the most help. Some people worry that birds will suffer unless they make great efforts to the feeder filled, but research indicates that most birds do not depend on feeders.

23 children (29% vs 17%; P.0008), and (CI): ), to beli Moderator: Vaccine attitudes (pre-treatment) s - s s s TABLE 2 Parental Perspectives on Vaccines Perspective Scale from Freed et al. (2010): Getting vaccines is a good way to protect my child(ren) from disease. Generally I do what my doctor recommends about vaccines for my child(ren). I am concerned about serious adverse effects of vaccines. New vaccines are recommended only if they are as safe as older vaccines. Parents should have the right to refuse vaccines that are required for school for any reason. Some vaccines cause autism in healthy children. My child(ren) does(do) not need vaccines for diseases that are not common anymore. % That Agree Provided by University of Michigan on May 13, 2010

24 DV: Vaccines cause autism Some vaccines cause autism in healthy children. Strongly agree Agree Neutral Disagree Strongly disagree

25 DV: Side effects Just based on what you know, how likely is it that children who get the measles, mumps, and rubella vaccine, which is known as the MMR vaccine, will suffer serious side effects? Very likely Somewhat likely Slightly likely Slightly unlikely Somewhat unlikely Very unlikely

26 DV: MMR intention If you had another child, how likely is it that you would give that child the measles, mumps, and rubella vaccine, which is known as the MMR vaccine? Very likely Somewhat likely Slightly likely Slightly unlikely Somewhat unlikely Very unlikely