Covid: qué es la miocarditis, por qué la asocian con las vacunas (y por qué no es alarmante) / Myocarditis After COVID Vaccination Is Rare, Resolves Quickly, Studies Confirm

El riesgo de miocarditis es una de las razones por las que algunas personas dudan sobre vacunarse o vacunar a sus hijos contra el coronavirus, pero ¿qué es esa condición y qué tan infundado es ese temor?

La palabra miocarditis empezó a aparecer en titulares y en cadenas de WhatsApp.

Una de las razones es que el Comité de Evaluación de Riesgos de Farmacovigilancia en Europa (PRAC, por sus siglas en inglés) recomendó incluirla como un nuevo efecto secundario de las vacunas de tecnología ARNm que se aplican contra el coronavirus.

Aunque concluyó, también, que la probabilidad de que esta ocurra es muy baja, hay quienes le temen al punto de preferir no vacunarse.

Aquí tres preguntas para entender mejor este tema:

  1. ¿Qué es la miocarditis?
    Es la inflamación del músculo del corazón conocido como miocardio, este se encarga de facilitar la contracción para bombear la sangre, así que cuando se inflama, ese movimiento se puede dificultar.

«El síntoma más común es dolor en el pecho y algunas personas pueden tener fiebre. En manifestaciones más severas puede haber falla en el corazón, es decir, que le falta el aire al paciente, puede presentarse hinchazón en las piernas y en casos muy muy severos podría incluso llevar a la muerte», explicó el doctor Jorge Salinas, médico infectólogo y epidemiólogo hospitalario en la Universidad de Stanford en entrevista con BBC Mundo.

  1. ¿Por qué aparece y cuál es su relación con la covid?
    La miocarditis puede aparecer «después de una infección, cualquiera que esta sea, o a causa de una falla en nuestro sistema inmune», dijo Salinas.

Así que, como la covid es un virus que infecta al organismo, puede causar que aparezca la inflamación.

«Algunos estudios han citado que la incidencia de la miocarditis es de más de 100 por 100.000 casos en personas con covid, mientras que la incidencia antes de que la covid existiera era entre uno y 10 casos por 100.000.

«En otras palabras, la infección por coronavirus parece aumentar el riesgo de desarrollar miocarditis en más de 10 veces», continúo.

Otro asunto es la severidad de la miocarditis, pues tal y como ocurre con el coronavirus, en la mayoría de los casos su afectación es leve, pero puede llegar a complicarse.

«Si uno deja actuar al sistema inmune por sí solo, la respuesta varía mucho entre persona y persona, pero si la persona esta vacunada y aparece la miocarditis, se sabe que esta tiende a ser leve», añadió.

  1. Vacunarse contra la covid ¿aumenta el riesgo, aunque sea leve?
    Según Salinas, no es totalmente claro que las vacunas causen miocarditis, pero podría pasar, aun así la incidencia es bastante baja.

Según un estudio israelí publicado en The New England Journal of Medicine y realizado en colaboración con la Universidad de Harvard y el Instituto de Investigación Clalit:

«Entre los pacientes de un gran sistema de salud israelí que habían recibido al menos una dosis de la vacuna de ARNm BNT162b2, la incidencia estimada de miocarditis fue de 2,13 casos por cada 100.000 personas; la incidencia más alta fue entre pacientes masculinos entre las edades de 16 y 29 años. La mayoría de los casos de miocarditis fueron de gravedad leve o moderada«.

De todas formas, explicó Salinas, «al vacunarnos, lo que estamos haciendo es disminuir el riesgo de tener miocarditis. Porque si usted no se vacuna va a tener covid y si tiene covid el riesgo de miocarditis es mayor y su severidad puede ser impredecible».

«Si usted se vacuna su riesgo es menor y si es que le llegara a dar miocarditis, lo más probable es que esta sea leve», agregó.

Ahora, supongamos que una persona tiene alguna condición cardiaca, por lo que teme que al vacunarse esta empeore.

En ese caso «la enfermedad por covid pone en riesgo su vida, así que el riesgo de enfermarse severamente es mayor que el que se puede tener con una miocarditis leve y poco probable asociada a la vacuna», indicó Salinas.

«La maravilla de las vacunas es que entrenan a nuestro cuerpo para que no nos infectemos y para que aún si nos infectamos este pueda reaccionar de una manera ordenada.

«Cuando el virus llega al cuerpo, establece una serie de barreras ordenadas para combatirlo; sin embargo, cuando uno no está vacunado y el virus entra al cuerpo, el sistema inmune puede actuar de manera desesperada y, en este caso, puede producir una miocarditis», concluyó el experto.
Por BBC News Mundo –

Myocarditis After COVID Vaccination Is Rare, Resolves Quickly, Studies Confirm

Data from the CDC and from a comparison of mRNA and inactivated vaccine add reassurance about risks in young people.

Myocarditis is rare after vaccination for COVID-19, two new studies affirm, with a rapid onset of symptoms and a mild disease course that resolves with pain medication and no adverse outcomes. Both studies highlight the low risk of myocarditis compared with the known benefits of vaccination.

In the first study, researchers led by Matthew E. Oster, MD, MPH (Centers for Disease Control and Prevention, Atlanta, GA), report on over 1,600 cases of myocarditis that occurred following vaccination with the BNT162b2 vaccine (Pfizer/BioNTech) or the mRNA-1273 vaccine (Moderna) and were reported to the Vaccine Adverse Event Reporting System (VAERS). More than 80% of those cases occurred in males ages 16 to 31 years, with rapid symptom onset occurring primarily after a second dose. While the vast majority required hospitalization (96%), symptoms were resolved completely in 87% by hospital discharge, with 87% requiring only nonsteroidal anti-inflammatory drugs (NSAIDs) and no reported deaths.

Commenting for TCTMD, Biykem Bozkurt, MD, PhD (Baylor College of Medicine, Houston TX), said the new CDC data are confirmatory of earlier reports but also offer a larger sample size, with data through August 2021. She was lead author of a paper last summer that provided a comprehensive review of available evidence on vaccine-related myocarditis cases reported in VAERS and from the Vaccine Safety Datalink (VSD), as well as reports from the US Department of Defense and the Israeli Ministry of Health.

“We know myocarditis is rare in terms of its absolute risk. The risk is higher for younger ages and predominantly males. Interestingly, in this analysis, they’re actually providing US subgroup risk profiles that are clarifying the highest-risk group as being 16 to 17 years of age for males,” Bozkurt noted. She added that compared with prior reports from VAERS showing an overall risk of myocarditis ranging from one in 16,000 to one in 20,000 for individuals ages 12-17, the new CDC estimate lowers that to about one in 14,000 for ages 12-15 and one in 9,500 for ages 16-17, and the risk decreases with increasing age.

Since the earliest reports of myocarditis in vaccinated patients, the Vaccine Safety Technical (VaST) Work Group has said they believe there is a “likely association” between myocarditis and mRNA vaccines in adolescents and young adults, with cases predominantly being seen after the second dose in males.

In the report by Oster and colleagues, published today in JAMA, the median time to symptom onset after a second dose was 2 days, with 90% of myocarditis events occurring within 7 days. Individuals with vaccine-related myocarditis were primarily of white (69%) or Hispanic ethnicity (17%). By vaccine type, 947 myocarditis patients received Pfizer/BioNTech and 382 received Moderna. Although myocarditis cases were reported in females, the rates were lower than in males across all age groups under age 50, Oster and colleagues found.

Of the 1,600 cases, 1,305 occurred in patients under age 30. The most commonly reported symptoms were chest pain, pressure, or discomfort in 89%, followed by dyspnea or shortness of breath in 30%. Nearly all patients had elevated troponin levels (98%), and 72% had an abnormal electrocardiogram. Only two required intubation or mechanical ventilation, and none required heart transplant, extracorporeal membrane oxygenation, or a ventricular assist device.

“Even though almost all individuals with cases of myocarditis were hospitalized and clinically monitored, they typically experienced symptomatic recovery after receiving only pain management,” Oster and colleagues write. They add that the risk of myocarditis “should be considered in the context of the benefits of COVID-19 vaccination.”

Comparing mRNA and Inactive Vaccine-Related Myocarditis

The second study, published online ahead of print, in Annals of Internal Medicine, and led by Francisco Tsz Tsun Lai, PhD (Hong Kong Special Administrative Region, China), examined data on 160 hospitalized patients aged 12 years or older with a first diagnosis of carditis (myocarditis or pericarditis) according to ICD-9-CM codes, and 1,533 hospitalized control participants without carditis. Of the latter group, 10 were randomly matched with each case patient by age, sex, and admission date. All admissions occurred between February and August 2021.

Patients were classified as unvaccinated, or as having received one or two doses of either the Pfizer/BioNTech or the CoronaVac vaccine (Sinovac Life Sciences). Unlike Pfizer/BioNTech or Moderna, which utilize mRNA technology, CoronaVac is an inactivated SARS-CoV-2 vaccine.

The majority of patients in the study were not vaccinated (n = 1,408). Among those who were, seven confirmed carditis cases occurred with CoronaVac versus 20 with Pfizer/BioNTech. In the Pfizer/BioNTech-vaccinated patients, the risk was most frequently seen after the second dose, with a doubling of the odds ratio compared with the first dose. The cumulative incidence of carditis after vaccination was 0.57 (CI 0.36-0.90) per 100,000 doses with Pfizer/BioNTech and 0.31 (CI 0.13-0.66) per 100,000 doses with CoronaVac, driven by myocarditis rather than pericarditis. Symptom onset occurred in the first week after vaccination in 75% of all carditis cases vaccinated with Pfizer/BioNTech and more than 30 days after vaccination in most of those who received CoronaVac.

According to Lai and colleagues, none of the 20 patients with carditis after Pfizer/BioNTech vaccination were admitted to the ICU or died within the observation period, as compared with 14 of 133 unvaccinated patients, 12 of whom died. The absolute risk of myocarditis after Pfizer/BioNTech vaccination was 0.25 per 100,000 after the first dose and approximately one per 100,000 after the second dose.

In an email, senior author Ian C.K. Wong, PhD (Hong Kong Special Administrative Region, China), said the absence of an association between carditis and CoronaVac suggests that it “might be specific to mRNA vaccines, which is consistent with the existing literature.” As with Oster and colleagues, Lai et al say the increased risk of vaccine-related myocarditis “should be made known to vaccine recipients and physicians and be weighed against the benefits of vaccination.”

Follow-up and Causality

Bozkurt said the Hong Kong data support current thinking that there is no association between preexisting conditions or comorbidities and vaccine-associated myocarditis. She also noted that despite the reassuring data from both studies, long-term follow-up is still needed to fully understand the health implications of vaccine-associated myocarditis. Oster and colleagues say the CDC has started active surveillance in adolescents and young adults to assess health, functional status, and cardiac outcomes at 3-6 months in probable and confirmed cases.

The message about myocarditis risk also needs to be paired with information on what COVID-19 can do to the heart. Bozkurt pointed to a recent paper in the New England Journal of Medicine that showed an 18-fold higher risk of myocarditis and substantially higher risks of arrhythmia, MI, deep vein thrombosis, pulmonary embolism, and pericarditis in unvaccinated people infected with SARS-CoV-2 compared with those vaccinated with Pfizer/BioNTech. Another recent study in Nature Medicine that compared Pfizer/BioNTech, Moderna, and AstraZeneca’s ChAdOx1 vaccine found one to 10 extra myocarditis cases per 1,000,000 vaccinations versus 40 extra per 1,000,000 with SARS-CoV-2 infection. That study also hinted at a potential dose-response gradient with higher mRNA-dose vaccines in younger individuals.

To TCTMD, Wong said his group believes myocarditis is likely related to the immune response triggered by vaccination, a response that is typically stronger in younger people.

“Currently, we are working with stem cell researchers to explore the possibilities of examining the specific mechanism that explains these differences using different biomedical models as well,” Wong said. “We agree that young males, or their parents, should be made aware of this elevated risk after the second dose and seek medical help if needed.”

Bozkurt said while a dysregulated immune response is one theory, testosterone could play a role, as could molecular mimicry between components of the vaccine, such as the spike protein, and production of self-antigens or autoantibodies. Either way, she said experimental, translational, and clinical studies are needed to further understand vulnerability to vaccine-associated myocarditis.

“There is a necessity for clarifying genetic predisposition, maladaptive immune response, dysregulated immune response, and whether augmentation of certain type of cells in the immune response is playing a role,” she said.

For the big picture, Bozkurt said all evidence points to vaccine-related myocarditis being self-limited with no long-term sequelae, whereas myocarditis with SARS-CoV-2 is not mild and is associated with increased death. “If people are worried about their heart, the infection itself is a much higher risk than not getting the vaccine,” she added.
by L.A. McKeown