ARE SYNCOPES COMMON IN TEENAGERS AFTER VACCINATION?
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Introduction
It is generally accepted that adolescents are more likely than other age groups to experience episodes of syncope following vaccine administration or venous infusion. In fact, in 2011, the Institute of Medicine published a summary of 12 studies that concluded that there was a causal relationship between syncope and parenteral vaccine administration (Straton K, Institute of Medicine, 2011). However, for various reasons, the true incidence of these events is unknown.
Although vasovagal syncope itself is not dangerous, it can lead to falls that cause various types of injuries (CDC, MMWR 2008). Recently, a teenager in France died from a head injury due to vasovagal syncope after vaccination (Dib F, J Adolesc Health 2024). In fact, the ACIP (Advisory Committee on Immunization Practices) recommended in 2006, after the inclusion of HPV, Men ACWY, and Tdpa vaccines in the adolescent immunization schedule, that a period of observation after vaccination be maintained to reduce the risk of vasovagal syncope-related injuries (Kroger AT, MMWR 2006).
Recently, the results of a study were published describing the incidence of vasovagal syncope and its potential consequences after vaccination in adolescents aged 9-18 years, recorded in the electronic clinical records of an integrated health care system (Kaiser Permanente Northwest) from 2013 to 2019 (Groom HC, J Adolesc Health 2024).
In this note we summarize the main results of the study.
Key Results
During the study period, a total of 197,642 vaccinations and 12,246 vein extractions were recorded. In 70% of cases, one vaccine was administered, in 17% two vaccines were administered simultaneously, and in 13% three or more vaccines were administered simultaneously.
Fainting after vaccination
The electronic clinical record recorded a diagnosis of syncope associated with vaccination in 549 adolescents. 81% of the syncope events reported occurred before vaccination, and only in 70 cases after vaccination. Of these 70 syncope events, 59 (84%) occurred immediately after vaccination, and the remaining 11 were attributed by medical personnel to venous blood sampling performed after vaccine administration. 
The incidence of vasovagal syncope following vaccination was 10.7% (59/549). That The global incidence of post-vaccination syncope was 2.99 per 10,000 vaccinations. (IC95·%: from 2.27 to 3.85). The incidence by sex was the same (3.72 in women/2.28 in men). By age, the highest incidence was observed in the 9-12 year old group (4.58/10,000; 95% CI from 3.24 to 6.29). In the 13-15 year old age group, the incidence was 1.52/10,000; 95% CI from 0.65 to 2.99, and in the 16-18 year old group it was 2.10/10,000; 95% CI from 1.12 to 3.59 (Fig. 2).
Regarding the number of vaccines administered, the incidence after administration of one vaccine was 1.51/10,000 vaccinations (95% CI 0.93 to 2.30), compared with 3.92 (95% CI 2.09 to 6.70) after co-administration of two vaccines and 9.94 (95% CI 6.43 to 14.67) after administration of three or more vaccines. The incidence of syncope was similar in those who received the HPV vaccine and those who did not (Figure·3). 
The incidence of syncope after blood sampling was 16.33/10,000 samples. Thus, syncope was observed significantly less frequently after vaccine administration than after venipuncture (incidence rate 0.18, 95% CI 0.11 to 0.31).
Postsyncopal injuries
There were 12 post-syncope injuries, 11 of which occurred to the head or face and were minor contusions that did not require medical attention or follow-up. Only one patient sustained a contusion that took several days to heal.
Discussion
Some vaccine safety studies in the US have found syncope rates associated with Tdpa vaccination in adolescents at 0.13/10,000 doses (Chang S, Vaccine 2013) and with HPV vaccines at 0.47–0.82/10,000 doses (Ji J, Vaccine 2011). A study in Australia found a syncope rate of 2.69/10,000 HPV doses in 12–13 year olds (Philips A, Vaccine 2020).
There are no data on the association between syncope and the number of vaccines administered in adolescents. This study shows a syncope rate of up to 9.9 per 10,000 doses when 3 or more vaccines were administered, with no significant differences by age group. It is important to keep in mind that the ACIP recommendations for adolescent vaccination call for three vaccines (Tdpa, MenACWY, HPV) to be administered simultaneously, so a study that takes into account the effect of age and the number of vaccines administered would be desirable. vaccines administered on the development of post-vaccination syncope.
One article reported that in adults, the incidence of syncope increased by 286% when 3 or more vaccines were administered at the same time (AFHSC, MSMR 2013).
Another interesting point is that while previous articles have suggested an association between the HPV vaccine and syncope (Arana JE, Vaccine 2018) (Slade BA, JAMA 2009), this study did not prove that HPV vaccination was associated with a higher incidence of syncope.
conclusions
– The incidence of fainting after vaccination was 2.99/10,000 vaccinations, which is clearly lower than the incidence of fainting after blood sampling.
– The incidence of syncope was higher when more than one vaccine was administered simultaneously.
– There was no difference in the incidence of syncope with or without HPV vaccine.
– Injuries occurred in 15% of patients with vasovagal syncope, most of them were minor and did not require assistance.
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Bibliographic references
- Arana J.E., and others. Postlicensure safety monitoring of a quadrivalent human papillomavirus vaccine in the Vaccine Adverse Event Reporting System (VAERS), 2009-2015. Vaccine 2018; 36:1781e8
- Military Health Surveillance C. Syncope, Active and Reserve Components, U.S. Armed Forces, 1998–2012. MSMR 2013;20:5e9
- CDC. Fainting after vaccination – United States, January 2005 – July 2007. MMWR Morb Mortal Wkly Rep. 2008;57:457e60
- Chang S. and others. Postlicensure safety surveillance of tetanus, diphtheria, and acellular pertussis vaccines for adolescents and adults in the United States: 2005–2007. Vaccine 2013;31:1447e52
- Dib F, and others. When immunization-related stress response (ISRR) interrupts school vaccination programs: the case of France. J Adolescent Health 2024; 74:857
- GJ, and others. Monitoring the safety of a quadrivalent human papillomavirus vaccine: results from an analysis of vaccine safety data. Vaccine 2011;29:8279e84
- Kroger A.T., and others. General recommendations for immunization: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recommendation Report 2006;55(RR-15):1-48
- Groom HC, and others. Incidence of adolescent syncope and related injuries after vaccination and routine venipuncture. J Adolescent Health. 2024;74(4):696-702
- Phillips A. and others. Adverse events following HPV vaccination: 11 years of follow-up in Australia. Vaccine 2020;38:6038e46
- Slade B.A. Postlicensing safety surveillance of a quadrivalent recombinant human papillomavirus vaccine. JMA 2009; 302:750
- Straton K. and others. Institute of Medicine. Vaccine Adverse Events: Evidence for Causality. Washington, DC: National Academies Press; 2011.