Importance Parents hesitant to vaccinate their children may delay routine immunizations or seek exemptions from state vaccine mandates. Recent outbreaks of vaccine-preventable diseases in the United States have drawn attention to this phenomenon. Improved understanding of the association between vaccine refusal and the epidemiology of these diseases is needed. Objective To review the published literature to evaluate the association between vaccine delay, refusal, or exemption and the epidemiology of measles and pertussis, 2 vaccine-preventable diseases with recent US outbreaks. Evidence Review Search of PubMed through November 30, 2015, for reports of US measles outbreaks that have occurred since measles was declared eliminated in the United States (after January 1, 2000), endemic and epidemic pertussis since the lowest point in US pertussis incidence (after January 1, 1977), and for studies that assessed disease risk in the context of vaccine delay or exemption. Findings We identified 18 published measles studies (9 annual summaries and 9 outbreak reports), which described 1416 measles cases (individual age range, 2 weeks-84 years; 178 cases younger than 12 months) and more than half (56.8%) had no history of measles vaccination. Of the 970 measles cases with detailed vaccination data, 574 cases were unvaccinated despite being vaccine eligible and 405 (70.6%) of these had nonmedical exemptions (eg, exemptions for religious or philosophical reasons, as opposed to medical contraindications; 41.8% of total). Among 32 reports of pertussis outbreaks, which included 10 609 individuals for whom vaccination status was reported (age range, 10 days-87 years), the 5 largest statewide epidemics had substantial proportions (range, 24%-45%) of unvaccinated or undervaccinated individuals. However, several pertussis outbreaks also occurred in highly vaccinated populations, indicating waning immunity. Nine reports (describing 12 outbreaks) provided detailed vaccination data on unimmunized cases; among 8 of these outbreaks from 59% through 93% of unvaccinated individuals were intentionally unvaccinated. Conclusions and Relevance A substantial proportion of the US measles cases in the era after elimination were intentionally unvaccinated. The phenomenon of vaccine refusal was associated with an increased risk for measles among people who refuse vaccines and among fully vaccinated individuals. Although pertussis resurgence has been attributed to waning immunity and other factors, vaccine refusal was still associated with an increased risk for pertussis in some populations.

Anaphylaxis is a potentially life-threatening allergic reaction. The risk of anaphylaxis after vaccination has not been well described in adults or with newer vaccines in children. We sought to estimate the incidence of anaphylaxis after vaccines and describe the demographic and clinical characteristics of confirmed cases of anaphylaxis. Using health care data from the Vaccine Safety Datalink, we determined rates of anaphylaxis after vaccination in children and adults. We first identified all patients with a vaccination record from January 2009 through December 2011 and used diagnostic and procedure codes to identify potential anaphylaxis cases. Medical records of potential cases were reviewed. Confirmed cases met the Brighton Collaboration definition for anaphylaxis and had to be determined to be vaccine triggered. We calculated the incidence of anaphylaxis after all vaccines combined and for selected individual vaccines. We identified 33 confirmed vaccine-triggered anaphylaxis cases that occurred after 25,173,965 vaccine doses. The rate of anaphylaxis was 1.31 (95% CI, 0.90-1.84) per million vaccine doses. The incidence did not vary significantly by age, and there was a nonsignificant female predominance. Vaccine-specific rates included 1.35 (95% CI, 0.65-2.47) per million doses for inactivated trivalent influenza vaccine (10 cases, 7,434,628 doses given alone) and 1.83 (95% CI, 0.22-6.63) per million doses for inactivated monovalent influenza vaccine (2 cases, 1,090,279 doses given alone). The onset of symptoms among cases was within 30 minutes (8 cases), 30 to less than 120 minutes (8 cases), 2 to less than 4 hours (10 cases), 4 to 8 hours (2 cases), the next day (1 case), and not documented (4 cases). Anaphylaxis after vaccination is rare in all age groups. Despite its rarity, anaphylaxis is a potentially life-threatening medical emergency that vaccine providers need to be prepared to treat.

We computed the annual change in the rates of nonmedical exemptions from school immunization requirements and compared these rates between states that allow philosophical exemptions and states that allow only religious exemptions. We also compared states with respect to how difficult it is to obtain nonmedical exemptions because of certain administrative procedures. We used data compiled by the Centers for Disease Control and Prevention (CDC) for school years 2005–2006 through 2010–2011.¹ State-specific categories of difficulty in obtaining exemptions were based on several factors: whether completion of a standardized form was permissible, as opposed to a letter from a parent; where the parent obtained the form (i.e., school vs. health department); whether the form had to be notarized; and whether a letter from a parent, if required, needed to be worded a specific way, resulting in extra effort on the part of the parent.

OBJECTIVE: Previous surveys on hypothesized sexual activity changes after human papillomavirus (HPV) vaccination may be subject to self-response biases. To date, no studies measured clinical markers of sexual activity after HPV vaccination. This study evaluated sexual activity–related clinical outcomes after adolescent vaccination. METHODS: We conducted a retrospective cohort study utilizing longitudinal electronic data from a large managed care organization. Girls enrolled in the managed care organization, aged 11 through 12 years between July 2006 and December 2007, were classified by adolescent vaccine (HPV; tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis, adsorbed; quadrivalent meningococcal conjugate) receipt. Outcomes (pregnancy/sexually transmitted infection testing or diagnosis; contraceptive counseling) were assessed through December 31, 2010, providing up to 3 years of follow-up. Incidence rate ratios comparing vaccination categories were estimated with multivariate Poisson regression, adjusting for health care–seeking behavior and demographic characteristics. RESULTS: The cohort included 1398 girls (493 HPV vaccine–exposed; 905 HPV vaccine–unexposed). Risk of the composite outcome (any pregnancy/sexually transmitted infection testing or diagnosis or contraceptive counseling) was not significantly elevated in HPV vaccine–exposed girls relative to HPV vaccine–unexposed girls (adjusted incidence rate ratio: 1.29, 95% confidence interval [CI]: 0.92 to1.80; incidence rate difference: 1.6/100 person-years; 95% CI: −0.03 to 3.24). Incidence rate difference for Chlamydia infection (0.06/100 person-years [95% CI: −0.30 to 0.18]) and pregnancy diagnoses (0.07/100 person-years [95% CI: −0.20 to 0.35]), indicating little clinically meaningful absolute risk differences. CONCLUSIONS: HPV vaccination in the recommended ages was not associated with increased sexual activity–related outcome rates.

Background. Influenza infection during pregnancy is associated with adverse fetal outcomes such as preterm birth and small for gestational age (SGA). Maternal influenza immunization may prevent these adverse infant outcomes during periods of influenza circulation. Methods. We conducted a retrospective cohort study of live births within Kaiser Permanente (KP) Georgia and Mid-Atlantic States (n = 3327) during the period of 2009 influenza A (H1N1) virus circulation. Primary outcomes were third-trimester preterm birth (27–36 weeks), birth weight, low birth weight (LBW, <2500 g), and SGA. Results. There were 327 (9.8%) preterm, 236 (7.4%) LBW, and 267 (8.4%) SGA births. Among H1N1-vaccinated mothers (n = 1125), there were 86 (7.6%) preterm, 68 (6.4%) LBW, and 99 (9.3%) SGA births, and the mean birth weight was 3308.5 g (95% confidence interval [CI], 3276.6–3340.4). Among unvaccinated mothers (n = 1581), there were 191 (12.1%) preterm, 132 (8.8%) LBW, and 123 (8.2%) SGA births, and the mean birth weight was 3245.3 g (95% CI, 3216.5–3274.2). Infants of H1N1-vaccinated mothers had 37% lower odds of being born preterm than infants of unvaccinated mothers (adjusted odds ratio, 0.63 [95% CI, .47–.84]). The mean birth weight difference between infants of H1N1-vaccinated mothers and infants of unvaccinated mothers was 45.1 g (95% CI, 1.8–88.3). There was no significant association between maternal H1N1 influenza immunization and LBW or SGA. Conclusions. Pregnant women who received H1N1 influenza vaccine were less likely to give birth preterm, and gave birth to heavier infants. The findings support US vaccine policy choices to prioritize pregnant women during the 2009 influenza A (H1N1) pandemic.

Pertussis (whooping cough) is a vaccine-preventable illness that has been increasing in incidence over the past decade in the United States.^1-3 Neonates and infants are at increased risk of pertussis-related hospitalization and death compared with older children and adults. Many public health strategies have been recommended to decrease the burden of pertussis in neonates and infants.^4-6 Most recently, in 2012, the Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) recommended tetanus, diphtheria, and acellular pertussis (Tdap) vaccination for all pregnant women during each pregnancy regardless of prior immunization status.⁶