One of the ongoing concerns of COVID-19 vaccines has been reports around thromboembolic and cardiovascular events. There have been reports of blood clots following adenovirus-based COVID-19 vaccines, with an association that was further assessed in observational studies. Later on, mRNA-based vaccines were found to be associated with the risk of rare myocarditis events.

Contrary to these past associations, a new study published in the journal, Heart, reported there was a major reduction of risk (45–81%) for thromboembolic and cardiac events for post-acute COVID-19 venous thromboembolism (VTE), arterial thrombosis/thromboembolism (ATE) and heart failure (HF) in patients who had been vaccinated.

“Vaccination against SARS-CoV- 2 substantially reduced the risk of acute post-COVID- 19 thromboembolic and cardiac complications, probably through a reduction in the risk of SARS-CoV- 2 infection and the severity of COVID-19 disease due to vaccine-induced immunity,” the study authors wrote.

The Study’s Parameters and Findings
The investigators performed a staggered cohort study based on national vaccination campaigns using EHR from the UK, Spain and Estonia. Vaccine rollout was grouped into 4 stages with predefined enrollment periods. The study included 10.17 million vaccinated and 10.39 million unvaccinated people.

Each stage included all individuals eligible for vaccination, with no previous COVID-19 infection or vaccine at the start date. Vaccination status was used as a time-varying exposure. Outcomes included the 3 aforementioned adverse events: HF, VTE, and ATE. The 4 windows of post infection: 0–30, 31–90, 91–180 and 181–365 days.

The vaccines used for the study were approved within the study period from January 2021 to July 2021, including the ChAdOx1 (Oxford/AstraZeneca), BNT162b2 (Pfizer-BioNTech) Ad26.COV2.S (Janssen). and mRNA-1273 (Moderna).

VTE:
“Reduced risk associated with vaccination is observed for acute and post-acute VTE, DVT, and PE: acute meta-analytic sHR are 0.22 (95% CI, 0.17–0.29); 0.36 (0.28–0.45); and 0.19 (0.15–0.25), respectively. For VTE in the post-acute phase, sHR estimates are 0.43 (0.34–0.53), 0.53 (0.40–0.70) and 0.50 (0.36–0.70) for 31–90, 91–180, and 181–365 days post COVID-19, respectively,” the investigators reported.

ATE:
“Similarly, the risk of ATE, IS and MI in the acute phase after infection was reduced for the vaccinated group, sHR of 0.53 (0.44–0.63), 0.55 (0.43–0.70) and 0.49 (0.38–0.62), respectively. Reduced risk associated with vaccination persisted for post-acute ATE, with sHR of 0.74 (0.60–0.92), 0.72 (0.58–0.88) and 0.62 (0.48–0.80) for 31–90, 91–180 and 181–365 days post-COVID- 19, respectively,” they wrote.

HF:
“Meta-analytic estimates in the acute phase showed sHR of 0.45 (0.38–0.53) for HF, 0.41 (0.26– 0.66) for MP and 0.41 (0.27–0.63) for VACA. Reduced risk persisted for post-acute COVID-19 HF: sHR 0.61 (0.51–0.73) for 31–90 days, 0.61 (0.51–0.73) for 91–180 days and 0.52 (0.43–0.63) for 181–365 days,” the investigators noted. “For post-acute MP, risk was only lowered in the first post-acute window (31–90 days), with sHR of 0.43 (0.21–0.85). Vaccination showed no association with post-COVID- 19 HS.”

The Length of the Vaccine’s Efficacy
In terms of the vaccine’s benefit against VTE, ATE, and HF, the investigators said the protection against the events lasted up to 1 year; although it was not clear for other complications. 

The investigators also noted that new research would be needed to determine the possible waning of the risk reduction over time as well as the impact of booster vaccination.

Reference
Mercadé-Besora N, Li X, Kolde R, et al. The role of COVID-19 vaccines in preventing post-COVID-19 thromboembolic and cardiovascular complications. Heart. Published online March 12, 2024. doi:10.1136/heartjnl-2023-323483