A re-assessment of 4CMenB vaccine effectiveness against serogroup B invasive meningococcal disease in England based on an incidence model

Background The four-component serogroup B meningococcal 4CMenB vaccine (Bexsero, GSK) has been routinely given to all infants in the United Kingdom at 2, 4 and 12 months of age since September 2015. After 3 years, Public Health England (PHE) reported a 75% [95% confidence interval 64%; 81%] reduction in the incidence of serogroup B invasive meningococcal disease (IMD) in age groups eligible to be fully vaccinated. In contrast, vaccine effectiveness (VE) evaluated in the same immunization program applying the screening method was not statistically significant. We re-analyzed the data using an incidence model. Methods Aggregate data—stratified by age, year and doses received—were provided by PHE: serogroup B IMD case counts for the entire population of England (years 2011–2018) and 4CMenB vaccine uptake in infants. We combined uptake with national population estimates to obtain counts of vaccinated and unvaccinated person-time by age and time. We re-estimated VE comparing incidence rates in vaccinated and non-vaccinated subjects using a Bayesian Poisson model for case counts with person-time data as an offset. The model was adjusted for age, time and number of doses received. Results The incidence model showed that cases decreased until 2013–2014, followed by an increasing trend that continued in the non-vaccinated population during the immunization program. VE in fully vaccinated subjects (three doses) was 80.1% [95% Bayesian credible interval (BCI): 70.3%; 86.7%]. After a single dose, VE was 33.5% [12.4%; 49.7%]95%BCI and after two doses, 78.7% [71.5%; 84.5%]95%BCI. We estimated that vaccination averted 312 cases [252; 368]95%BCI between 2015 and 2018. VE was in line with the previously reported incidence reduction. Conclusions Our estimates of VE had higher precision than previous estimates based on the screening method, which were statistically not significant, and in line with the 75% incidence reduction previously reported by PHE. When disease incidence is low and vaccine uptake is high, the screening method applied to cases exclusively from the population eligible for vaccination may not be precise enough and may produce misleading point-estimates. Precise and accurate VE estimates are fundamental to inform public health decision making. VE assessment can be enhanced using models that leverage data on subjects not eligible for vaccination.

Nonspecific symptoms dominate at first contact to emergency healthcare services among cases with invasive meningococcal disease

Background An early appropriate response is the cornerstone of treatment for invasive meningococcal disease. Little evidence exists on how cases with invasive meningococcal disease present at first contact to emergency medical services. Methods Retrospective observational study of cases presenting with invasive meningococcal disease from January 1st of 2016 to December 31st of 2020 in the Capital Region of Denmark with a catchment area population of 1,800,000. A single medical emergency center provides services to the region. Data was collected from emergency medical services’ call audio files, data from the call receiver registrations, registrations from ambulance personal and electronic health record data from the hospitalization. Results Of 1527 cases suspected of meningitis, 38 had invasive meningococcal disease and had been in contact with the emergency service. Most contacts were to the medical helpline rather than the emergency call center at initial contact to emergency medical services. All were hospitalized within 12 h. At initial contact, fever was present in 28 (74%) of 38 cases, while specific symptoms such as headache (n=12 (32%)), a rash or petechiae (n=9 (23%)) and stiffness of the neck (n=4 (11%)) varied and were infrequent. Cases younger than 18 years of age were more often male and more often presented with fever and rash/petechiae. Only 4 (11%) received prehospital antibiotic treatment. Conclusions Cases with invasive meningococcal disease presented with fever and unspecific symptoms. Although few were acutely ill at their initial contact, all were admitted within 12 h. We suggest that all feverish cases should be systematically asked about specific symptoms and should be wary of symptom progression to optimize the early management if cases with invasive meningococcal disease.