DVT risk not raised after COVID-19 vaccination

There is no apparent increased risk of deep vein thrombosis (DVT) following receipt of the COVID-19 vaccine, according to a study presented at ASH 2021.

“Rates of thrombosis after COVID-19 vaccination are low and similar to what might be expected for population rates,” presented study author Dr Damon Houghton from the Gonda Vascular Center, Mayo Clinic, Rochester, Minnesota, US.

Using electronic medical records from the Mayo Clinic database, the researchers identified 382,524 adults (median age 61 years, 55.3 percent male) who had received ≥1 COVID-19 vaccination* between 1 November, 2020 and 1 June, 2021. They analysed acute upper and lower extremity DVT and pulmonary embolism (PE) venous Duplex ultrasound (DUS) examination reports that were conducted in 5,960 patients (7,265 ultrasounds) in the 90 days pre- and post-vaccination date (first dose for Pfizer and Moderna vaccines).

The Pfizer vaccine was the most commonly used (64.2 percent), followed by the Moderna and Janssen vaccines (31.6 and 4.3 percent, respectively). The mean age at vaccination was 61.0, 56.5, and 54.7 years for recipients of the Moderna, Pfizer, and Janssen vaccines, respectively. Women were more likely to receive the Pfizer compared to the Moderna or Janssen vaccines (56.3, 54.1, and 49.5 percent, respectively), while non-White vaccine recipients were more likely to receive the Janssen compared to the Moderna or Pfizer vaccines (21, 7.7, and 8.2 percent, respectively). Ninety-one percent of Pfizer vaccine recipients had received two doses compared with 82.4 percent of Moderna vaccine recipients.

Moderna vaccine recipients tended to have more comorbidities than Pfizer or Janssen vaccine recipients specifically cancer (20.5, 16.6, and 14.0 percent, respectively), diabetes (17.7, 13.8, and 14.7 percent), pulmonary disease (19.9, 18.2, and 18.2 percent), myocardial infarction or stroke (8.1, 6.5, and 6.1 percent), and renal disease (9.5, 7.6, and 6.4 percent).

Using the Natural Language Processing (NLP) algorithm, acute DVT was identified in 11.1 percent of ultrasounds (714 patients). This corresponded with an overall acute DVT rate of 1.86 per 1,000 patients. [ASH 2021, abstract 291]

When categorized by extremity, acute DVT was identified in 10.7 and 13.5 percent of lower and upper extremity DUS, respectively.

Acute DVT rates did not significantly differ between the post- and pre-vaccination periods (unadjusted hazard ratio [HR], 1.12, 95 percent confidence interval [CI], 0.97–1.29). However, an increased risk of PE was observed in the post-vaccination period (unadjusted HR, 1.21, 95 percent CI, 1.02–1.43).

Factors that may have influenced the elevated PE rate were surgery and hospitalization/emergency department (ED) visits – both of which were more common during the post-vaccination periods – and COVID-19 infection (more frequent pre-vaccination).

There was a trend toward increased risk of post-vaccination PE in individuals with a COVID-19 infection within 30 days pre-vaccination.

“[However,] COVID-19 infection prior to vaccination was not a risk factor for post-vaccination thrombosis,” noted Houghton.

When death was used as a competing risk for PE, after adjusting for pre- and post-vaccination surgeries, ED visits, hospitalization, COVID-19 infection, and non-angiogram CT scans, post-vaccination PE risk was not increased regardless of cancer presence or absence (HRs, 1.23 and 1.16, respectively).

The rates of thrombosis were generally low, said Houghton. PE events occurred in 0.08 vs 0.07 percent of vaccine recipients in the post- vs pre-vaccination period (p=0.04), while DVT occurred in 0.10 vs 0.09 percent (p=0.12). A total of 713 deaths occurred (0.19 percent).

Ninety days post-vaccination, the rates of DVT following receipt of the Pfizer or Janssen vaccine did not differ from that of the Moderna vaccine** (HR, 0.80, 95 percent CI, 0.98–1.25 and HR, 0.75, 95 percent CI, 0.42–1.32, respectively).

“We found no difference in post-vaccination DVT and PE between vaccines after adjustment,” said Houghton.

“Approved vaccines for COVID-19 are effective in preventing infection and serious illness. There have, however, been rare and unusual thrombotic events associated with thrombocytopenia that have been observed with some of these vaccines. We’ve also witnessed thrombotic events in close proximity to vaccination; this has led to speculation about thrombotic risk more generally with these vaccines,” he said.

“Compared to baseline pre-vaccination rates, there was no significant increase in the post-vaccination risk of DVT and PE more generally,” he added.