Neal A. Halsey

Bio: Neal A. Halsey is an academic researcher from Johns Hopkins University. The author has contributed to research in topics: Vaccination & Population. The author has an hindex of 67, co-authored 348 publications receiving 15851 citations. Previous affiliations of Neal A. Halsey include Centers for Disease Control and Prevention & Syracuse University.

Vaccine refusal, mandatory immunization, and the risks of vaccine-preventable diseases

Abstract: Vaccines are among the most effective prevention tools available to clinicians. However, the success of an immunization program depends on high rates of acceptance and coverage. There is evidence of an increase in vaccine refusal in the United States and of geographic clustering of refusals that results in outbreaks. Children with exemptions from school immunization requirements (a measure of vaccine refusal) are at increased risk for measles and pertussis and can infect others who are too young to be vaccinated, cannot be vaccinated for medical reasons, or were vaccinated but did not have a sufficient immunologic response. Clinicians can play a crucial role in parental decision making. Health care providers are cited as the most frequent source of immunization information by parents, including parents of unvaccinated children. Although some clinicians have discontinued or have considered discontinuing their provider relationship with patients who refuse vaccines, the American Academy of Pediatrics Committee on Bioethics advises against this and recommends that clinicians address vaccine refusal by respectfully listening to parental concerns and discussing the risks of nonvaccination.

Factors Associated With Refusal of Childhood Vaccines Among Parents of School-aged Children: A Case-Control Study

Abstract: Background The rate of nonmedical exemptions to school immunization requirements has been increasing, and children with exemptions have contributed to outbreaks of vaccine-preventable diseases. Objectives To determine why parents claim nonmedical exemptions and to explore differences in perceptions of vaccines and vaccine information sources between parents of exempt and fully vaccinated children. Design Case-control study. Setting Colorado, Massachusetts, Missouri, and Washington. Participants Surveys were mailed to the parents of 815 exempt children (cases) and 1630 fully vaccinated children (controls randomly selected from the same grade and school) recruited from 112 private and public elementary schools. Surveys were completed by 2435 parents (56.1%). Main Outcome Measures Parental reports. Results Most children (209 [75.5%] of 277) with nonmedical exemptions received at least some vaccines. The most common vaccine not received was varicella (147 [53.1%] of 277 exempt children). The most common reason stated for requesting exemptions (190 [69%] of 277) was concern that the vaccines might cause harm. Parents of exempt children were significantly more likely than parents of vaccinated children to report low perceived vaccine safety and efficacy, a low level of trust in the government, and low perceived susceptibility to and severity of vaccine-preventable diseases. Parents of exempt children were significantly less likely to report confidence in medical, public health, and government sources for vaccine information and were more likely to report confidence in alternative medicine professionals than parents of vaccinated children. Conclusion Continued efforts must be made to educate parents about the utility and safety of vaccines, especially parents requesting nonmedical exemptions to school immunization requirements.

The Clinical Significance of Measles: A Review

Abstract: Forty years after effective vaccines were licensed, measles continues to cause death and severe disease in children worldwide. Complications from measles can occur in almost every organ system. Pneumonia, croup, and encephalitis are common causes of death; encephalitis is the most common cause of long-term sequelae. Measles remains a common cause of blindness in developing countries. Complication rates are higher in those 20 years old, although croup and otitis media are more common in those <2 years old and encephalitis in older children and adults. Complication rates are increased by immune deficiency disorders, malnutrition, vitamin A deficiency, intense exposures to measles, and lack of previous measles vaccination. Case-fatality rates have decreased with improvements in socioeconomic status in many countries but remain high in developing countries.

Immunization responses in rheumatoid arthritis patients treated with rituximab: results from a controlled clinical trial.

Abstract: Objective To examine immunization responses in patients with rheumatoid arthritis (RA) treated with rituximab and to investigate the effects of rituximab-induced CD20+ B cell depletion on immune responses to tetanus toxoid (T cell–dependent antigen), pneumococcal polysaccharide (T cell–independent antigen), and keyhole limpet hemocyanin (KLH) (neoantigen) and on delayed-type hypersensitivity (DTH). Methods In a controlled trial, we enrolled 103 patients with active RA receiving a stable dose of methotrexate (MTX). Tetanus toxoid, pneumococcal polysaccharide, and KLH vaccines as well as a Candida albicans skin test were administered to 1 group of patients receiving rituximab plus MTX (called rituximab-treated patients) for 36 weeks and to 1 group of patients receiving MTX alone for 12 weeks. The primary end point was the proportion of patients with a ≥4-fold rise in antitetanus IgG levels. Antitetanus, antipneumococcal, and anti-KLH serum IgG levels were measured prior to and 4 weeks following vaccine administration. The DTH response to C albicans was measured 2–3 days following placement. Results Responses to tetanus toxoid vaccine (≥4-fold rise) were similar in both groups (39.1% of rituximab-treated patients and 42.3% of patients treated with MTX alone). The ability to maintain a positive DTH response to the C albicans skin test was comparable in both groups (77.4% of rituximab-treated patients and 70% of patients treated with MTX alone), showing no effect of rituximab treatment. Rituximab-treated patients had decreased responses to pneumococcal polysaccharide vaccine (57% of patients had a 2-fold rise in titer in response to ≥1 serotype, compared with 82% of patients treated with MTX alone) and to KLH vaccine (47% of patients had detectable anti-KLH IgG, compared with 93% of patients treated with MTX alone). Conclusion Recall responses to the T cell–dependent protein antigen tetanus toxoid as well as DTH responses were preserved in rituximab-treated RA patients 24 weeks after treatment. Responses to neoantigen (KLH) and T cell–independent responses to pneumococcal vaccine were decreased, but many patients were able to mount responses. These data suggest that polysaccharide and primary immunizations should be administered prior to rituximab infusions to maximize responses.

Nonmedical exemptions to school immunization requirements: secular trends and association of state policies with pertussis incidence.

Abstract: ContextSchool immunization requirements have played a major role in controlling vaccine-preventable diseases in the United States. Most states offer nonmedical exemptions to school requirements (religious or personal belief). Exemptors are at increased risk of acquiring and transmitting disease. The role of exemption policies may be especially important for pertussis, which is endemic in the United States.ObjectiveTo determine if (1) the rates of nonmedical exemptions differ and have been increasing in states that offer only religious vs personal belief exemptions; (2) the rates of nonmedical exemptions differ and have been increasing in states that have easy vs medium and easy vs difficult processes for obtaining exemptions; and (3) pertussis incidence is associated with policies of granting personal belief exemptions, ease of obtaining exemptions, and acceptance of parental signature as sufficient proof of compliance with school immunization requirements.Design, Setting, and ParticipantsWe analyzed 1991 through 2004 state-level rates of nonmedical exemptions at school entry and 1986 through 2004 pertussis incidence data for individuals aged 18 years or younger.Main Outcome MeasuresState-level exemption rates and pertussis incidence.ResultsFrom 2001 through 2004, states that permitted personal belief exemptions had higher nonmedical exemption rates than states that offered only religious exemptions, and states that easily granted exemptions had higher nonmedical exemption rates in 2002 through 2003 compared with states with medium and difficult exemption processes. The mean exemption rate increased an average of 6% per year, from 0.99% in 1991 to 2.54% in 2004, among states that offered personal belief exemptions. In states that easily granted exemptions, the rate increased 5% per year, from 1.26% in 1991 to 2.51% in 2004. No statistically significant change was seen in states that offered only religious exemptions or that had medium and difficult exemption processes. In multivariate analyses adjusting for demographics, easier granting of exemptions (incidence rate ratio = 1.53; 95% confidence interval, 1.10-2.14) and availability of personal belief exemptions (incidence rate ratio = 1.48; 95% confidence interval, 1.03-2.13) were associated with increased pertussis incidence.ConclusionsPermitting personal belief exemptions and easily granting exemptions are associated with higher and increasing nonmedical US exemption rates. State policies granting personal belief exemptions and states that easily grant exemptions are associated with increased pertussis incidence. States should examine their exemption policies to ensure control of pertussis and other vaccine-preventable diseases.

The Mathematics of Infectious Diseases

Abstract: Many models for the spread of infectious diseases in populations have been analyzed mathematically and applied to specific diseases. Threshold theorems involving the basic reproduction number $R_{0}$, the contact number $\sigma$, and the replacement number $R$ are reviewed for the classic SIR epidemic and endemic models. Similar results with new expressions for $R_{0}$ are obtained for MSEIR and SEIR endemic models with either continuous age or age groups. Values of $R_{0}$ and $\sigma$ are estimated for various diseases including measles in Niger and pertussis in the United States. Previous models with age structure, heterogeneity, and spatial structure are surveyed.