Risk of Serious Blood Clot Events Spike In The Months After COVID-19

黃文英

New observational research out of Sweden has tracked more than one million COVID-19 cases for months after their acute illness in order to determine how the disease influences subsequent risk of blood clots. The findings indicate COVID-19 significantly increases a person's risk of deep vein thrombosis and pulmonary embolism in the months after infection.

The large study，published in The BMJ，looked at health data from 1，057，174 positive COVID-19 cases. This covers every single positive recorded case in Sweden from the beginning of the pandemic up to May 2021. A control group of four million age- and sex-matched subjects not positive with COVID was generated to quantify the increase in risk for blood clots caused by infection.

In the 30 days after an initial COVID-19 diagnosis the researchers found a 33- fold increase in pulmonary embolism risk，a five-fold increase in deep vein thrombosis （DVT）risk and a two- fold increase in general bleeding events. The heightened risk，compared to the uninfected control group，persisted 60 days for bleeding，90 days for DVT，and 180 days for pulmonary embolism.

瑞典一項觀察研究對100多萬新冠病例進行了數月追蹤，以確定新冠是如何影響感染者隨后出現血栓的風險的。研究結果表明，人們在感染新冠后幾個月內深靜脈血栓形成和肺栓塞的風險明顯增加。

這項研究樣本龐大，對1057174新冠病毒陽性感染者的健康數據進行了分析，涵蓋了瑞典從疫情暴發以來到2021年5月的所有陽性感染者。研究設置了一個對照組，從而量化感染新冠導致的血栓風險增加程度，對照組由400萬年齡和性別相仿的受試者組成，這些受試者的新冠病毒檢測結果未呈陽性。該研究發表在《英國醫學雜志》上。

研究人員發現，感染者在最初確診新冠30天后，肺栓塞風險增加33倍，深靜脈血栓形成風險增加5倍，一般性出血事件風險增加2倍。與未感染新冠的對照組相比，出血風險升高持續60 天，深靜脈血栓形成風險升高持續90天，肺栓塞風險升高持續180天。

Factoring in acute disease severity，the researchers found those initially hit hardest with COVID-19 did experience greater long-term risk for blood clotting events. However，the increased risk was not zero in those experiencing mild COVID. Those with only a mild infection still showed a three-fold risk of DVT and a seven-fold risk of pulmonary embolism.

While this new study is the most robust to investigate the relationship between blood clots and SARS-CoV-2 infection it is not the first to identify this association. A large UK study last year found similar signs when it compared rates of hematological and vascular events after COVID-19 to rates of those same events after COVID vaccination.

That study more generally found significant increases in rates of stroke，heart attack and blood clotting a month after a COVID infection. It also found these rates of adverse events were much higher after CO VID- 19 than after vaccination，validating the suggestion that the deleterious after-effects of COVID-19 are much more impactful than any potential harms caused by vaccination.

Another UK study published last year found incidences of and deaths from thromboembolism doubled in the first six months of the pandemic compared to rates seen in the years prior.

Ioannis Katsoularis，an author on the new Swedish study from Umea University，said the findings affirm the value of vaccination in reducing the likelihood and severity of COVID- 19.

研究人員發現，重癥感染者血栓形成的風險更大。但輕癥感染者血栓形成的風險也有所增加。輕癥患者的深靜脈血栓形成風險增加3倍，而肺栓塞風險增加7倍。

該項最新研究是探索血栓形成與新冠病毒感染之間相關度的最有力研究，但它并不是第一項發現這種關聯的研究。2021年英國的一項大型研究也發現了類似跡象，該研究比較了感染新冠后與接種新冠疫苗后的血液血管疾病的發生率。

該研究更普遍地發現，在感染新冠一個月后，中風、心臟病發作和血栓的發生率顯著增加。研究還發現，在感染新冠后，這些疾病的發生率要比接種疫苗之后高得多，這驗證了新冠后遺癥的危害比接種疫苗造成的任何潛在危害的影響更大的觀點。

去年發布的另一項英國研究發現，在新冠疫情發生的前六個月，血栓栓塞癥的發病率和死亡率比前幾年翻了一番。

該最新研究的論文作者，瑞典于默奧大學的伊奧尼斯·卡蘇拉里斯稱，這些研究結果肯定了疫苗接種在降低感染風險和減少重癥方面的價值。