Active SMS-based influenza vaccine safety surveillance in Australian children

IntroductionAustralia’s novel, active surveillance system, AusVaxSafety, monitors the post-market safety of vaccines in near real time. We analysed cumulative surveillance data for children aged 6 months to 4 years who received seasonal influenza vaccine in 2015 and/or 2016 to determine: adverse event following immunisation (AEFI) rates by vaccine brand, age and concomitant vaccine administration.MethodsParent/carer reports of AEFI occurring within 3 days of their child receiving an influenza vaccine in sentinel immunisation clinics were solicited by Short Message Service (SMS) and/or email-based survey. Retrospective data from 2 years were combined to examine specific AEFI rates, particularly fever and medical attendance as a proxy for serious adverse events (SAE), with and without concomitant vaccine administration. As trivalent influenza vaccines (TIV) were funded in Australia’s National Immunisation Program (NIP) in 2015 and quadrivalent (QIV) in 2016, respectively, we compared their safety profiles.Results7402 children were included. Data were reported weekly through each vaccination season; no safety signals or excess of adverse events were detected. More children who received a concomitant vaccine had fever (7.5% versus 2.8%; p < .001). Meningococcal B vaccine was associated with the highest increase in AEFI rates among children receiving a specified concomitant vaccine: 30.3% reported an AEFI compared with 7.3% who received an influenza vaccine alone (p < .001). Reported fever was strongly associated with medical attendance (OR: 42.6; 95% Confidence Interval (CI): 25.6–71.0). TIV and QIV safety profiles included low and expected AEFI rates (fever: 4.3% for TIV compared with 3.2% for QIV (p = .015); injection site reaction: 1.9% for TIV compared with 3.0% for QIV (p < .001)). There was no difference in safety profile between brands.DiscussionActive participant-reported data provided timely vaccine brand-specific safety information. Our surveillance system has particular utility in monitoring the safety of influenza vaccines, given that they may vary in composition annually.     

Continuous active surveillance of adverse events following immunisation using SMS technology

IntroductionOn-going post-licensure surveillance of adverse events following immunisation (AEFI) is critical to detecting and responding to potentially serious adverse events in a timely manner. SmartVax is a vaccine safety monitoring tool that uses automated data extraction from existing practice management software and short message service (SMS) technology to follow-up vaccinees in real-time. We report on childhood vaccine safety surveillance using SmartVax at a medical practice in Perth, Western Australia.MethodsParents of all children under age five years who were vaccinated according to the Australian National Immunisation Schedule between November 2011 and June 2015 were sent an SMS three days post administration to enquire whether the child had experienced a suspected vaccine reaction. Affirmative replies triggered a follow-up SMS requesting details of the reaction(s) via a link to a survey that could be completed using a smartphone or the web. Rates of reported AEFI including fever, headache, fatigue, rash, vomiting, diarrhoea, rigours, seizures, and local reactions were calculated by vaccination time point.ResultsOverall, 239 (8.2%; 95% CI 7.2–9.2%) possible vaccine reactions were reported for 2897 vaccination visits over the 44 month time period. The proportion of children experiencing a possible AEFI, mostly local reactions, was significantly greater following administration of diphtheria–tetanus–pertussis–poliomyelitis vaccine at 4 years of age (77/441; 17.5%; 95% CI 13.9–21.0%) compared to the vaccinations given at 2–18 months (p < 0.001). Across all time points, local reactions and fatigue were the most frequently reported AEFI.ConclusionAutomated SMS-based reporting can facilitate sustainable, real-time, monitoring of adverse reactions and contribute to early identification of potential vaccine safety issues.     

Vaxtracker: Active on-line surveillance for adverse events following inactivated influenza vaccine in children

Vaxtracker is a web based survey for active post marketing surveillance of Adverse Events Following Immunisation. It is designed to efficiently monitor vaccine safety of new vaccines by early signal detection of serious adverse events. The Vaxtracker system automates contact with the parents or carers of immunised children by email and/or sms message to their smart phone. A hyperlink on the email and text messages links to a web based survey exploring adverse events following the immunisation. The Vaxtracker concept was developed during 2011 (n = 21), and piloted during the 2012 (n = 200) and 2013 (n = 477) influenza seasons for children receiving inactivated influenza vaccine (IIV) in the Hunter New England Local Health District, New South Wales, Australia. Survey results were reviewed by surveillance staff to detect any safety signals and compare adverse event frequencies among the different influenza vaccines administered. In 2012, 57% (n = 113) of the 200 participants responded to the online survey and 61% (290/477) in 2013. Vaxtracker appears to be an effective method for actively monitoring adverse events following influenza vaccination in children.     

Review of prescribing information for influenza vaccines for pregnant and lactating women

Information provided by most influenza vaccine manufacturers do not reflect the recommendations of WHO and/or national public health advisory groups with regard to the use of influenza vaccines in pregnant or lactating women. The majority of vaccines contain precautionary language which could discourage use in pregnant women and some include stronger language discouraging or contradicting use in pregnant or lactating women. Regulators and manufacturers should regularly assess the language of pregnancy and lactation sections in product information for vaccines and include information from national public health advisory groups regarding use by pregnant or lactating women and data from relevant studies.     

Safety profile of rubella vaccine administered to pregnant women: A systematic review of pregnancy related adverse events following immunisation,including congenital rubella syndrome and congenital rubella infection in the foetus or infant

BackgroundData on the safety of inadvertent rubella vaccination in pregnancy is important for rubella vaccination programs aimed at preventing congenital rubella syndrome.MethodsThe association between monovalent rubella or combination vaccinations in or shortly before pregnancy and potential harm to the foetus was examined by conducting a systematic review and meta-analysis using fixed effect methods and simulation.ResultsFour cohort studies of inadvertently vaccinated and unvaccinated women were found, 15 cohorts of pregnant women who were rubella susceptible at time of inadvertent vaccination and 9 cohort studies with no information on susceptibility and case series. No case of vaccine associated congenital rubella syndrome (CRS) was identified. Cohort studies with an unvaccinated comparison group were limited in number and size, and based on these only a theoretical additional risk of 6 or more cases of CRS per 1000 vaccinated women (0% observed, upper 95% CI 0.6%) could be excluded. Based on cohorts of vaccinated rubella susceptible pregnant women a maximum theoretical risk of 1 CRS case in 1008 vaccinated women (0% observed, upper 95% CI 0.099%) was estimated. Asymptomatic rubella vaccine virus infection of the neonate was also noted (fixed effects estimate of risk overall 1.74%, 95% CI 1.21, 2.28).ConclusionThere is no evidence that CRS is caused by rubella-containing vaccines but transplacental vaccine virus infection can occur. CRS is effectively prevented by vaccination, thus the risk/benefit balance is unequivocally in favour of vaccination. The data confirm previous recommendations that inadvertent vaccination during pregnancy is not an indication for termination of pregnancy.     

Value of an in-depth analysis of unpublished data on the safety of influenza vaccines in pregnant women

BackgroundUnpublished data can sometimes provide valuable information on the safety of biologic products.MethodsWe assessed information potentially available from regulatory authorities, manufacturers, and public health agencies. We explored 4 recently established vaccine registries, reviewed package inserts from 99 influenza vaccines, and contacted vaccine manufacturers and regulatory agencies for data on influenza vaccine safety in pregnant women.ResultsThe vaccine registries did not have sufficient data to analyze and there are problems with the quality of the information. The majority of package inserts provided no product-specific safety information for pregnant women, especially in less developed countries. The majority of available data come from reports gathered from passive adverse event reporting systems in the general population and reports of women enrolled in clinical trials of influenza vaccines who became pregnant at various times before or after receiving influenza vaccine. The information was not collected in a systematic manner, there are inconsistencies in the follow up of pregnant women and the available information about pregnancy outcomes. Considerable resources would be needed to systematically identify all of the information, try to obtain missing follow up information, and conduct analyses. There would be substantial limitations to any attempt to conduct a systematic analysis.ConclusionsThe value of trying to analyze unpublished data on the safety of influenza vaccine in pregnancy is limited and would require considerable resources to thoroughly investigate. Expanding efforts to identify and review unpublished data regarding the safety of influenza vaccines in pregnancy is not likely to produce information of high scientific value or information that could not be identified from publications and other publically available data.     

Enhanced surveillance for adverse events following immunization during the 2019 typhoid conjugate vaccine campaign in Harare,Zimbabwe

BackgroundDuring February 25–March 4, 2019, Zimbabwe’s Ministry of Health and Child Care conducted an emergency campaign using 342,000 doses of typhoid conjugate vaccine (TCV) targeting individuals 6 months–15 years of age in eight high-risk suburbs of Harare and up to 45 years of age in one suburb of Harare. The campaign represented the first use of TCV in Africa outside of clinical trials.MethodsThree methods were used to capture adverse events during the campaign and for 42 days following the last dose administered: (1) active surveillance in two Harare hospitals, (2) national passive surveillance, and (3) a post-campaign coverage survey.ResultsThirty-nine adverse events were identified during active surveillance, including 19 seizure cases (16 were febrile), 16 hypersensitivity cases, 1 thrombocytopenia case, 1 anaphylaxis case, and two cases with two conditions. Only 21 (54%) of 39 patients were hospitalized and 38 recovered without sequelae. Attack rates per 100,000 TCV doses administered were highest for seizures (6.27) and hypersensitivity (5.02). Only 6 adverse events were reported through passive surveillance by facilities other than the two active surveillance hospitals. A total of 177 (10%) of 1,817 vaccinees surveyed reported experiencing an adverse event during the post-campaign coverage survey, of which 25 (14%) sought care.ConclusionsIn line with previous evaluations of TCV, enhanced adverse event monitoring during an emergency campaign supports the safety of TCV. The majority of reported events were minor or resulted in recovery without long-term sequelae. Attack rates for seizures and hypersensitivity were low compared with previous active surveillance studies conducted in Kenya and Burkina Faso. Strengthening adverse event monitoring in Zimbabwe and establishing background rates of conditions of interest in the general population may improve future safety monitoring during new vaccine introductions.     

Active surveillance for influenza vaccine adverse events: the integrated vaccine surveillance system

Objectives

We conducted a pilot study of the Integrated Vaccine Surveillance System (IVSS), a novel active surveillance system for monitoring influenza vaccine adverse events that could be used in mass vaccination settings.

Methods

We recruited 605 adult vaccinees from a convenience sample of 12 influenza vaccine clinics conducted by public health departments of two U.S. metropolitan regions. Vaccinees provided daily reports on adverse reactions following immunization (AEFI) using an interactive voice response system (IVR) or the internet for 14 consecutive days following immunization. Followup with nonrespondents was conducted through computer-assisted telephone interviewing (CATI). Data on vaccinee reports were available real-time through a dedicated secure website.

Results

90% (545) of vaccinees made at least one daily report and 49% (299) reported consecutively for the full 14-day period. 58% (315) used internet, 20% (110) IVR, 6% (31) CATI, and 16% (89) used a combination for daily reports. Of the 545 reporters, 339 (62%) reported one or more AEFI, for a total of 594 AEFIs reported. The majority (505 or 85%) of these AEFIs were mild symptoms.

Conclusions

It is feasible to develop a system to obtain real-time data on vaccine adverse events. Vaccinees are willing to provide daily reports for a considerable time post vaccination. Offering multiple modes of reporting encourages high response rates. Study findings on AEFIs showed that the IVSS was able to exhibit the emerging safety profile of the 2008 seasonal influenza vaccine.     

Investigating adverse events following immunisation with pneumococcal polysaccharide vaccine using electronic General Practice data

BackgroundIn early 2011, following an increased number of reports of severe vaccine-related injection site reactions, Australian authorities recommended against administering repeat doses of the 23-valent pneumococcal polysaccharide vaccine (23vPPV) in otherwise healthy adults. The aim of this study was to assess a source of electronic medical record data from primary care providers (General Practitioners, GPs), for validity and ability to retrospectively detect this adverse event signal.MethodsThe General Practice Research Network (GPRN) holds data routinely collected from a representative sample of Australian GPs. Data were extracted on persons 18 years or older who had received at least one dose of 23vPPV or influenza vaccine (as comparator) between January 2002 and June 2012. Increases above background levels were assessed using 95% confidence intervals of reaction rates, calculated from the Poisson distribution of counts.ResultsThere was an average of 253 practices and 532 GPs contributing data per year. Over the study period there were 95,760 recorded 23vPPV administrations and 823 reactions, of which 233 were local. For influenza vaccine the numbers were 683,829 doses, 3001 and 387 respectively. Patterns of vaccinations and reactions were consistent with known safety profiles. There were 3 local reactions following 23vPPV in early 2011 (235/100,000 doses, 95% CI 49–717), which was not significantly different to the historical average (260, 225–298). We estimate that this system could have detected a 3-fold increase over background levels.ConclusionsUsing GP consultation data, we were unable to confirm an increase in local reactions detected by passive surveillance, suggesting that this apparent signal was artefactual. GP consultation data captures large numbers of vaccine recipients and medically attended adverse reactions at low cost. If available in a timely manner and expanded, this system has significant potential for use in validation of apparent signals from passive surveillance.     

Post-marketing surveillance of adverse events following immunization with inactivated quadrivalent and trivalent influenza vaccine in health care providers in Western Australia

In 2015, inactivated quadrivalent influenza vaccine (QIV) was first introduced into the Australian market. A routine vaccine safety surveillance system in Western Australia was used to conduct post-licensure surveillance of adverse events following immunization with inactivated QIV and trivalent influenza vaccines (TIV) in a sample of 1685 healthcare providers (HCPs). A similar percentage of HCPs who received QIV reported having any reaction seven days post-vaccination as HCPs who received TIV (13.6 vs. 12.8%, respectively; p = 0.66). However, a slightly higher percentage of HCPs who received QIV reported pain or swelling at the injection site as compared to HCPs who received TIV (6.9% vs. 4.2%, respectively; p = 0.02). No serious vaccine-associated adverse events were detected during follow-up of either vaccine. Acknowledging the study limitations, the results of this post-marketing surveillance support the safety of QIV, suggesting there is little difference in the reactogenicity of QIV as compared to TIV.     

Spontaneous reporting of adverse events following immunisation against pandemic influenza in Denmark November 2009-March 2010

Our study reviews the spontaneous reports of adverse events following immunisation submitted to the Danish Medicines Agency during the 2009-2010 influenza A/H1N1v season. During the study period (4 November 2009-31 March 2010), 607 reports comprising 1885 adverse events were reported among 339,507 influenza A/H1N1v vaccinated individuals (reporting rate, 179 per 100,000 vaccinated). The majority of individual case safety reports (85%) were submitted by physicians and other health care professionals and concerned known and non-serious reactions occurring within 1 day of vaccination (82%). Events of special interest as defined by EMA prior to vaccination campaign start, comprised 1% of all events. In conclusion, we did not observe any strong signals of any unknown or serious adverse events associated with influenza A/H1N1v vaccination in Denmark. Our experience also demonstrates the well-known limitations of spontaneous reports with respect to evaluation of a casual relationship and highlights the importance for a timely availability of background events rates and the need for new approaches to study late adverse effects following immunisation.     

Willingness to receive a vaccine is influenced by adverse events following immunisation experienced by others

An adverse event following immunization (AEFI) can have consequences for an individual’s future decision making and may contribute to vaccine hesitancy. AEFIs vary in severity and can be experienced directly (by an individual themselves) or indirectly (through witnessed or recounted events). We sought to measure the prevalence of specific AEFIs and understand which AEFIs have the greatest associations with reduced willingness to receive a vaccine and how injection anxiety may moderate the relationship.We conducted a cross-sectional online survey with both qualitative and quantitative elements in a sample of adults aged 18 years and over in Australia. Nineteen percent of the 1050 respondents reported experiencing an AEFI that they found stressful. Those who experienced an AEFI reported significantly higher levels of injection anxiety than those who did not. Within the group who reported experiencing an AEFI, respondents were significantly less likely to be willing to receive a COVID-19 vaccine if they reported: indirect exposure to an uncommon/rare AEFI compared with other AEFIs (aOR:0.39; 95% CI: 0.18–0.87); indirect exposure to a scientifically unsupported AEFI compared with other AEFIs (aOR:0.18; 95% CI: 0.05–0.57). Direct exposure to an AEFI was not associated with willingness to receive a COVID-19 vaccine. For those who reported experiencing an AEFI, the odds of willingness to receive a COVID-19 vaccine decreased significantly with an increase in injection anxiety (aOR:0.94; 95% CI: 0.9–0.98).Our results suggest that more is needed to mitigate the consequences of AEFIs on vaccine willingness. Empathically acknowledging at a community level, the experience of both real and perceived AEFIs and incorporating accounts of positive vaccination experiences in vaccine hesitancy interventions may be useful.     

Comparison of text-messaging to voice telephone interviews for active surveillance of adverse events following immunisation

ObjectivesIn 2013, the Follow-up and Active Surveillance of Trivalent Influenza Vaccine in Mums (FASTMum) program began using short message service (SMS) to collect adverse event information in pregnant women who recently received trivalent influenza vaccine (TIV). This study was designed to compare data collected via SMS and telephone for the purposes of monitoring vaccine safety.MethodsA number of 344 women who received TIV were randomly assigned to a telephone interview group. They were telephoned seven days post-vaccination and administered a standard survey soliciting any adverse events following immunisation (AEFI) they experienced. They were matched by brand of vaccine, age group, and residence to 344 women who were sent a SMS seven days post-vaccination. The SMS solicited similar information. AEFI reported by SMS and telephone interview were compared by calculating risk ratios.ResultsResponse rate was higher to SMS compared to telephone interview (90.1% vs. 63.9%). Women who were surveyed by SMS were significantly less likely to report an AEFI compared to women who were surveyed by telephone (RR: 0.41; 95% CI: 0.29–0.59). The greatest discrepancies between SMS and telephone interview were for self-reported injection site reactions (3.1% vs. 16.8%) and unsolicited (or “other”) events (11.4% vs. 4.1%). Data collected by SMS was significantly timelier.ConclusionsData collection by SMS results in significantly improved response rates and timeliness of vaccine safety data. Systems which incorporate SMS could be used to more rapidly detect safety signals and promote more rapid public health response to vaccine quality issues.     

Parental perspectives of vaccine safety and experience of adverse events following immunisation

Introduction

We aimed to determine demographic predictors of parental vaccine safety and risk perceptions, and assess the relationship between the occurrence of children's perceived adverse events following immunisation (AEFI) on parents’ opinions.

Methods

Computer-assisted telephone interviews (CATI) were conducted in 2011 with a cross-sectional, random general population sample of rural and metropolitan residents in South Australia. Multivariate ordinal logistic regression analyses examined associations between parental vaccine safety attitudes and socio-demographic factors, adjusting for whether children had ever experienced a previous suspected AEFI.

Results

Of 469 parents interviewed, 95% were confident in vaccine safety in general, but almost half expressed concern for pre-licensure testing of vaccines. Of all parents, 41% responded that at least one of their children had experienced an AEFI. Almost one third of the AEFI parent group indicated they reported their children's symptoms to either a healthcare professional or the Department of Health. Parental acceptability of the risks of febrile convulsion and anaphylaxis were 73% and 76% respectively. Ordinal logistic regression analyses showed parents of children who had experienced a suspected AEFI were associated with greater concern for vaccine safety (OR:0.53, p ≤ 0.01) and more were likely to expect either a mild or a serious AEFI. After adjusting for demographics, parental confidence in vaccine safety was significantly associated with higher levels of education (OR:2.58, p = 0.01) and being born in Australia OR:2.30, p = 0.004. Mothers, when compared with fathers, were less accepting of the two vaccine risks presented: febrile convulsion (OR:0.57, p = 0.04) and anaphylaxis, (OR:0.55, p = 0.04).

Conclusions

Parents commonly perceive and report that their child has experienced an AEFI. In this group of parents the subsequent expectation of an AEFI and vaccine safety concerns may be heightened. Further research should investigate parental understandings of differentiating an expected event from an adverse event as this could inform immunization risk communication and consumer AEFI reporting strategies.     

Participant centred safety surveillance of health care workers receiving influenza vaccination

Following the introduction of mandatory influenza vaccination for staff working in high risk clinical areas in 2018, we conducted active surveillance for adverse events following immunisation utilising an automated online survey to vaccine recipients at three and 42?days post immunisation. Most participants 2285 (92%) agreed to participate; 515 (32%) staff reported any symptom and eight (1.6%) sought medical attention. The odds of having a reaction decreased with age by approximately 2% per year. The system was acceptable to staff, and the data demonstrated rates of reported symptoms within expected rates for influenza vaccines from clinical trials. Rates of medical attendance were similar to previous surveillance. Participant centred real-time safety surveillance proved useful in this staff influenza vaccination context, providing reassurance with expected rates and profile of common adverse events following staff influenza vaccination.     

Building capacity for active surveillance of vaccine adverse events in the Americas: A hospital-based multi-country network

New vaccines designed to prevent diseases endemic in low and middle-income countries are being introduced without prior utilization in countries with robust vaccine pharmacovigilance systems. Our aim was to build capacity for active surveillance of vaccine adverse events in the Americas. We describe the implementation of a proof-of-concept study for the feasibility of an international collaborative hospital-based active surveillance system for vaccine safety. The study was developed and implemented in 15 sentinel sites located in seven countries of the region of the Americas, under the umbrella of the World Health Organization (WHO) Global Vaccine Safety Initiative. The study evaluated the associations between measles-mumps-rubella vaccines and two well-recognized adverse events: Immune thrombocytopenic purpura (ITP) and aseptic meningitis. The regional network contributed 63 confirmed ITP and 16 confirmed aseptic meningitis eligible cases to the global study, representing, respectively, 33% and 19% of the total cases. To ensure long-term sustainability and usefulness to investigate adverse events following new vaccine introductions in low and middle-income countries, the network needs to be strengthened with additional sites and integrated into national health systems.     

Postlicensure surveillance for pre-specified adverse events following the 13-valent pneumococcal conjugate vaccine in children

Although no increased risk was detected for serious adverse events in the prelicensure trials for the 13-valent pneumococcal vaccine, Prevnar 13^® (PCV13), continued monitoring of rare but serious adverse events is necessary. A surveillance system using cohort study design was set up to monitor safety of PCV13 immediately after it was included in the childhood immunization program in the United States. The exposed population included children of 1 month to 2 years old who received PCV13 from April, 2010 to January, 2012 from the eight managed care organizations participating in the Vaccine Safety Datalink Project in the United States. The historical unexposed population was children of the same age who received the 7-valent pneumococcal conjugate vaccine Prevnar 7^® (PCV7) in 2007 (or 2005 depending on the outcome of interest) to 2009. The risk of pre-specified adverse events in the risk window following PCV13 was repeatedly compared to that in the historical comparison group. The number of doses included in the study was 599,229. No increased risk was found for febrile seizures, urticaria or angioneurotic edema, asthma, thrombocytopenia, or anaphylaxis. An increased risk for encephalopathy was not confirmed following the medical record review. The relative risk for Kawasaki disease in 0–28 days following vaccination was 1.94 (95% confidence interval: 0.79–4.86), comparing PCV13 to PCV7. Comparing to PCV7 vaccine, we identified no significant increased risk of pre-specified adverse events in the Vaccine Safety Datalink study cohort. The possible association between PCV13 and Kawasaki disease may deserve further investigation.     

Surveillance of influenza immunisation uptake in people aged under 65 years with chronic disease

Historically, it has been difficult to obtain population based data on the uptake of influenza immunisation in people aged under 65 years who are at risk of serious illness or death from influenza and its complications. Data obtained electronically from 96% of all practices in Wales demonstrated that uptake in this group is low, with only a quarter of eligible patients immunised. Uptake varies considerably between patient groups and between geographical areas. This suggests an opportunity for significant health gain from targeted interventions to improve uptake.     

A systematic review of adverse events following immunization during pregnancy and the newborn period

In 2013, the WHO Strategic Advisory Group of Experts on Immunization (SAGE) requested WHO to develop a process and a plan to move the maternal immunization agenda forward in support of an increased alignment of data safety evidence, public health needs, and regulatory processes. A key challenge identified was the continued need for harmonization of maternal adverse event following immunization (AEFI) research and surveillance efforts within developing and developed country contexts. We conducted a systematic review as a preliminary step in the development of standardized AEFI definitions for use in maternal and neonatal clinical trials, post-licensure surveillance, and other vaccine studies. We documented the current extent and nature of variability in AEFI definitions and adverse event reporting among 74 maternal immunization studies, which reported a total of 240 different types of adverse events. Forty-nine studies provided explicit AEFI case definitions describing 35 separate types of AEFIs. We identified variability in how AEFIs were determined to be present, in how AEFI definitions were applied, and in the ways that AEFIs were reported. Definitions for key maternal/neonatal AEFIs differed on four discrete attributes: overall level of detail, physiological and temporal boundaries and cut-offs, severity strata, and standards used. Our findings suggest that investigators may proactively address these inconsistencies through comprehensive and consistent reporting of AEFI definitions and outcomes in future publications. In addition, efforts to develop standardized AEFI definitions should generate definitions of sufficient detail and consistency of language to avoid the ambiguities we identified in reviewed articles, while remaining practically applicable given the constraints of low-resource contexts such as limited diagnostic capacity and high patient throughput.