Hospitalizations within 14days of vaccination among pediatric recipients of the live attenuated influenza vaccine, United States 2010-2012

Myopericarditis following COVID-19 vaccination and non-COVID-19 vaccination: a systematic review and meta-analysis

Background

Myopericarditis is a rare complication of vaccination. However, there have been increasing reports of myopericarditis following COVID-19 vaccination, especially among adolescents and young adults. We aimed to characterise the incidence of myopericarditis following COVID-19 vaccination, and compare this with non-COVID-19 vaccination.

Methods

We did a systematic review and meta-analysis, searching four international databases from Jan 1, 1947, to Dec 31, 2021, for studies in English reporting on the incidence of myopericarditis following vaccination (the primary outcome). We included studies reporting on people in the general population who had myopericarditis in temporal relation to receiving vaccines, and excluded studies on a specific subpopulation of patients, non-human studies, and studies in which the number of doses was not reported. Random-effects meta-analyses (DerSimonian and Laird) were conducted, and the intra-study risk of bias (Joanna Briggs Institute checklist) and certainty of evidence (Grading of Recommendations, Assessment, Development and Evaluations approach) were assessed. We analysed the difference in incidence of myopericarditis among subpopulations, stratifying by the type of vaccine (COVID-19 vs non-COVID-19) and age group (adult vs paediatric). Among COVID-19 vaccinations, we examined the effect of the type of vaccine (mRNA or non-mRNA), sex, age, and dose on the incidence of myopericarditis. This study was registered with PROSPERO (CRD42021275477).

Findings

The overall incidence of myopericarditis from 22 studies (405 272 721 vaccine doses) was 33·3 cases (95% CI 15·3–72·6) per million vaccine doses, and did not differ significantly between people who received COVID-19 vaccines (18·2 [10·9–30·3], 11 studies [395 361 933 doses], high certainty) and those who received non-COVID-19 vaccines (56·0 [10·7–293·7], 11 studies [9 910 788 doses], moderate certainty, p=0·20). Compared with COVID-19 vaccination, the incidence of myopericarditis was significantly higher following smallpox vaccinations (132·1 [81·3–214·6], p<0·0001) but was not significantly different after influenza vaccinations (1·3 [0·0–884·1], p=0·43) or in studies reporting on various other non-smallpox vaccinations (57·0 [1·1–3036·6], p=0·58). Among people who received COVID-19 vaccines, the incidence of myopericarditis was significantly higher in males (vs females), in people younger than 30 years (vs 30 years or older), after receiving an mRNA vaccine (vs non-mRNA vaccine), and after a second dose of vaccine (vs a first or third dose).

Interpretation

The overall risk of myopericarditis after receiving a COVID-19 vaccine is low. However, younger males have an increased incidence of myopericarditis, particularly after receiving mRNA vaccines. Nevertheless, the risks of such rare adverse events should be balanced against the risks of COVID-19 infection (including myopericarditis).

Funding

None.

Evaluation of the safety of live attenuated influenza vaccine (LAIV) in children and adolescents with asthma and high-risk conditions: a population-based prospective cohort study conducted in England with the Clinical Practice Research Datalink

OBJECTIVES

To assess the safety of live attenuated influenza vaccine (LAIV) in children in high-risk groups.

DESIGN

Non-interventional cohort study.

SETTING

England during 2013-2014 and 2014-2015 influenza seasons.

PARTICIPANTS

LAIV recipients identified from the Clinical Practice Research Datalink, aged 2-17 years, and with at least one underlying high-risk condition. LAIV recipients were matched with inactivated influenza vaccine (IIV) recipients and unvaccinated controls.

PRIMARY OUTCOME MEASURES

Primary safety endpoints were any hospitalisation documented in the linked Hospital Episodes Statistics database within 42 days and up to 6 months after vaccination.

RESULTS

11 463 children and adolescents were included: 4718 received the trivalent LAIV formulation during the 2013-2014 influenza season and 6745 received the quadrivalent formulation during the 2014-2015 influenza season. The risks of hospitalisation within 42 days were 231 per 1000 person-years (95% CI 193 to 275) in season 2013-2014 and 231 (95% CI 198 to 267) in season 2014-2015. These risks were not significantly different when compared with matched unvaccinated children (relative risks (RR) 0.96 (95% CI 0.78 to 1.19) in season 2013-2014, 0.90 (95% CI 0.76 to 1.07) in season 2014-2015) and consistently lower than after IIV administration (RR 0.47 (95% CI: 0.37 to 0.59) in season 2013-2014, 0.42 (95% CI 0.35 to 0.51) in season 2014-2015). A similar pattern was observed up to 6 months postvaccination with a risk of hospitalisation after LAIV administration that did not differ from what was observed in unvaccinated controls and was lower than after IIV administration.

CONCLUSIONS

This study did not identify new safety concerns associated with the administration of LAIV in children and adolescents with high-risk conditions. However, as with any other observational study, treatment administration was not randomly assigned and our findings may be confounded by differences between the groups at baseline.

TRIAL REGISTRATION NUMBER

EUPAS18527.

Generalized herd effects and vaccine evaluation: impact of live influenza vaccine on off-target bacterial colonisation

Interactions between pathogens and commensal microbes are major contributors to health and disease. Infectious diseases however are most often considered independent, viewed within a one-host one-pathogen paradigm and, by extension, the interventions used to treat and prevent them are measured and evaluated within this same paradigm. Vaccines, especially live vaccines, by stimulating immune responses or directly interacting with other microbes can alter the environment in which they act, with effects that span across pathogen species. Live attenuated infl uenza vaccines for example, while safe, increase upper respiratory tract bacterial carriage density of important human commensal pathogens like Streptococcus pneumoniae and Staphylococcus aureus. Further, by altering the ecological niche and dynamics of phylogenetically distinct microbes within the host, vaccines may unintentionally affect transmission of non-vaccine targeted pathogens. Thus, vaccine effects may span across species and across scales, from the individual to the population level. In keeping with traditional vaccine herd-effects that indirectly protect even unvaccinated individuals by reducing population prevalence of vaccine-targeted pathogens, we call these cross-species cross-scale effects "generalized herd-effects". As opposed to traditional herd-effects, "generalized" relaxes the assumption that the effect occurs at the level of the vaccine-target pathogen and "herd effect" implies, as usual, that the effects indirectly impact the population at large, including unvaccinated bystanders. Unlike traditional herd-effects that decrease population prevalence of the vaccine-target, generalized herd-effects may decrease or increase prevalence and disease by the off-target pathogen. LAIV, for example, by increasing pneumococcal density in the upper respiratory tract of vaccine recipients, especially children, may increase pneumococcal transmission and prevalence, leading to excess pneumococcal invasive disease in the population, especially among the elderly and others most susceptible to pneumococcal disease. However, these effects may also be beneficial, for example the large reductions in all-cause mortality noted following measles vaccines. Here we discuss evidence for these novel vaccine effects and suggest that vaccine monitoring and evaluation programs should consider generalized herd effects to appreciate the full impacts of vaccines, beneficial or detrimental, across species and scales that are inevitably hiding in plain sight, affecting human health and disease.