From January 1 to June 20, 2019, 1,077 individual cases of measles have been confirmed in 28 states. This is the greatest number of cases reported in the U.S. since measles was declared eliminated in 2000.
We retrieved data from the Vaccine Adverse Event Reporting System (VAERS) database, a national post-licensure vaccine safety surveillance system, through the CDC WONDER interface for reports of children aged 12 months to 6 years vaccinated with the MMR vaccine in the U.S. between January 1, 1989 and January 1, 2019. Specific ADRs evaluated in this analysis included anaphylaxis, febrile seizures, encephalitis, and orchitis. Disproportionate reporting of ADRs was assessed using proportional reporting ratios (PRRs) to identify possible new vaccine safety signals.
A total of 158,602 ADR reports were identified for the MMR vaccine (all manufactures) and 329,379 reports for all other vaccines. No disproportionate reporting of any AE was found, except for orchitis, even though we might expect to see a higher proportion of these ADRs with the MMR vaccine than for all other vaccines.
The findings of this analysis appear to be reassuring as we found no disproportionate reporting of ADRs historically associated with the MMR vaccine as compared to all other vaccines over a period of 30 years. Although vaccine safety may be a well-known fact for healthcare providers, the use of the CDC WONDER interface and PRRs is an easy and quick way to reassure clinicians and patients regarding vaccine safety.
Vaccine, Safety, Measles, Mumps, Rubella, Adverse reactions, Adverse events, VAERS, Reporting system
VAERS: Vaccine Adverse Event Reporting System; CDC: Centers for Disease Control and Prevention; MMR: Measles, Mumps and Rubella vaccine; ADRs: Adverse Drug Reactions; AE: Adverse Events; PRRs: Proportional Reporting Ratios
From January 1 to June 20, 2019, 1,077 individual cases of measles were confirmed in 28 states [1]. This is the greatest number of cases reported in the U.S. since measles was declared eliminated in 2000 [1]. Concerns about vaccine safety is a common reason parents express for refusing vaccinations for their children [2]. The CDC Wide-ranging Online Data for Epidemiologic Research (CDC WONDER) is a system developed to promote information-driven decision making and provide access to detailed public health information to healthcare providers [3]. This study aims to evaluate reports submitted to the VAERS system of children exposed to the MMR vaccine and the speed, simplicity, and versatility of the CDC WONDER web interface.
We retrieved data from the Vaccine Adverse Event Reporting System (VAERS) database, a national post-licensure vaccine safety surveillance system, through the CDC WONDER interface for reports of children aged 12 months to 6 years vaccinated with the MMR vaccine in the U.S. between January 1, 1989 and January 1, 2019. Specific ADRs evaluated in this analysis included anaphylaxis, febrile seizures, encephalitis, orchitis, and idiopathic thrombocytopenic purpura. Disproportionate reporting of ADRs was assessed using proportional reporting ratios (PRRs) to identify possible new vaccine safety signals. This is a statistical aid to signal generation based on the proportionate approach and the stability of a large database. It involves the calculation of the proportions of specified reactions or groups of reactions of drugs of interest where the comparator is all other drugs in the database [4]. The result is the PRR where the PRR is a/(a + c) divided by b/(b + d) in a two by two table [4].
A total of 158,602 ADR reports were identified for the MMR vaccine (all manufactures) and 329,379 reports for all other vaccines (Table 1). ADRs terms with disproportionately higher reporting after MMR vaccine compared to all other vaccines were assessed using the criteria of Evans, et al. (PRR ≥ 2, the χ2 ≥ 4 with Yates correction, and the number of individual cases ≥ 3) [4]. No disproportionate reporting of any AE was found, except for orchitis (Table 2), even though we might expect to see a higher proportion of these ADRs with the MMR vaccine than for all other vaccines. We further evaluated disproportionate reporting of severe orchitis (defined as orchitis that resulted in death, permanent disability, life threatening, hospitalized, existing hospitalization prolonged, congenital anomaly or birth defect, as specified by the CDC WONDER "Serious" tab selection) and no disproportionate reporting was found.
Table 1: CDC WONDER reports retrieved. Anaphylaxis included anaphylactic reaction (122 MMR vaccine reports; 187 all other vaccines) and anaphylactic shock (8 MMR vaccine reports; 10 all other vaccines). ITP, idiopathic thrombocytopenic purpura; ADR, adverse drug reactions. View Table 1
Table 2: Proportional Reporting Ratios (PRR) analysis. Evans, et al. criteria for signal detection: PRR ≥ 2, the χ2 ≥ 4, and the number of individual cases ≥ 3.4 ITP, idiopathic thrombocytopenic purpura. View Table 2
Measles virus is highly infectious and, before the introduction of vaccines > 90% individuals were infected by age 10 [5]. The findings of this analysis appear to be reassuring as we found no disproportionate reporting of ADRs historically associated with the MMR vaccine as compared to all other vaccines over a period of 30 years [6]. Although vaccine safety may be a well-known fact for healthcare providers, the use of the CDC WONDER interface and PRRs is an easy and quick way to reassure clinicians and patients regarding vaccine safety.
All the listed authors contributed to the design and implementation of the research, to the analysis of the results and to the writing of the manuscript.