New Delhi: People who have received the one-shot Johnson & Johnson Covid vaccine may be at a higher risk of blood clots in the brain, compared to pre pandemic-rates, according to a study published in the journal JAMA Internal Medicine. This finding is especially applicable to women, the researchers from Mayo Clinic noted.
However, the researchers added that the risk of blood clots should be considered in context of the vaccine’s efficacy, saying it is effective in offering protection from severe Covid-19.
They added that the study does not establish direct causality; that is, it does not prove that the blood clots were caused by the J&J vaccine.
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Methodology
The study sought to investigate the prevalence of cerebral venous sinus thrombosis (CVST), which occurs when a blood clot forms in the brain’s venous sinuses and prevents blood from draining out of the brain.
It was based on two datasets. First, the researchers identified all the cases of CVST at Olmsted County in the US state of Minnesota from 1 January 2001 to 31 December 2015.
Then, using the US Centers of Disease Control’s Vaccine Adverse Event Reporting System (VAERS) data from 28 February 2021 (vaccine approval date) to 7 May, the researchers sought to estimate the incidence of CVST after vaccination with the Johnson & Johnson Ad26.CoV2.S vaccine.
According to their findings, 39 Olmsted County residents developed acute-incident CVST between 2001 and 2015. A total of 29 patients — or 74.4 per cent — had pre-existing risk factors for CVST, such as infection, active cancer or use of oral contraceptives in the preceding 92 days.
This translated to an overall CVST incidence rate of 2.34 per 100,000 person-years. Person-years is a type of measurement that takes into account both the number of people in a study and the amount of time each person spends in the study. For example, a study that followed 1,000 people for 1 year would contain 1,000 person-years of data.
Meanwhile, as of 7 May 2021, 46 potential CVST events, occurring within 92 days after vaccination, were reported to VAERS. Of these, eight cases were excluded because they were potentially duplicate reports or were not objectively diagnosed.
The overall CVST incidence rate post-vaccination was 8.65 per 100,000 person-years after 15 days, 5.02 per 100,000 person-years at 30 days, and 1.73 per 100,000 person-years at 92 days.
The post-vaccination CVST rate among females was over five times higher than the pre-Covid pandemic rate. The rate was highest among women aged between 40 and 49 years.
“We found that the CVST incidence rate 15 days after Ad26.COV2.S vaccination was significantly higher than the pre-pandemic rate. However, the higher rate of this rare adverse effect must be considered in the context of the effectiveness of the vaccine in preventing Covid-19,” the researchers said in their study.
They added that the risk of severe or critical Covid-19 was 940 per 100,000 person-years.
The team said it was unclear why women had a higher incidence of post-vaccination CVST.
(Edited by Sunanda Ranjan)
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