According to a Swedish study, after a Covid infection, there is an increased risk of having a major blood clot for the next six months. People with severe Covid, as well as those infected during the initial wave, had the highest clot risk. Therefore, the researchers emphasize the need of getting vaccinated against the virus. Blood clots can happen after immunization, but the risk is far lower, according to a major UK study. Patients who have received Covid-19 are more prone to develop a blood clot, especially those who have had to go to the hospital.
Scientists sought to know when the risk returns to normal and whether it has altered from one pandemic wave to the next. Between February 2020 and May 2021, the researchers followed the health of just over one million persons in Sweden who tested positive for Covid. They then compared them to four million others of the same age and sex who had never tested positive.
No certain explanation
The study concluded the following things. Those with Covid had an increased risk for clots in:
- leg, or deep vein thrombosis (DVT), for up to three months
- blood clots in the lungs, or pulmonary embolism, for up to six months
- internal bleeding, such as a stroke, for up to two months
When compared with those at normal risks, it was found that:
- Four out of every 10,000 Covid patients got DVT, compared to one out of every 10,000 non-Covid patients.
- A blood clot in the lung affected roughly 17 out of every 10,000 Covid patients, compared to less than one out of every 10,000 non-Covid patients.
The increased risk of blood clots was larger in the first wave than in later waves, according to the study. It is likely because treatments improved during the pandemic and older patients began to get vaccinated by the second wave. In those who were extremely critically unwell with Covid, the chance of a blood clot in the lung was 290 times higher than normal, and seven times higher than normal after moderate Covid. There is no certain explanation for why the clots occur. Vaccines are highly effective against severe Covid, but they provide less protection against infection.