People who have tested positive for coronavirus are at a “significantly increased” risk of developing blood clots for up to six months after infection, according to a new study.

Researchers found the risk of deep vein thrombosis (DVT) was “significantly” higher for three months after Covid infection, six months for pulmonary embolism (blocked blood vessel in the lungs), and two months for bleeding.

The findings show people with underlying health problems are most at risk, as are those with more severe Covid-19.

Risks were higher during the first wave of the pandemic compared to the second and third waves.

Researchers said this could reflect the role of vaccines and treatments, particularly for older people, in cutting their chances of suffering complications.

What you should do if you test positve for Covid

New finding ‘strengthen importance of vaccination’

For the research, experts from Umea University in Sweden looked at data for more than a million people in the country who tested positive between February 2020 and May 2021.

They were compared to more than four million people without the virus.

The team also looked at the risk of clots in the period after Covid symptoms began, compared to long before people tested positive, and long after their symptoms disappeared.

The results showed a five-fold increase in risk of deep vein thrombosis, a 33-fold increase in risk of pulmonary embolism, and an almost two-fold increase in risk of bleeding in the 30 days after infection.

In absolute terms, this means a first DVT occurred in 401 patients with Covid-19 (absolute risk 0.04%) and 267 patients without (absolute risk 0.01%) over this time period.

Meanwhile, a first pulmonary embolism occurred in 1,761 patients with Covid (absolute risk 0.17%) and 171 without (absolute risk 0.004%).

A first bleed occurred in 1,002 patients with Covid (absolute risk 0.10%) and 1,292 without (absolute risk 0.04%).

Risks continued for most patients for up to a period of six months.

The team concluded: “Our findings arguably support thromboprophylaxis (preventative treatment) to avoid thrombotic events, especially for high risk patients, and strengthen the importance of vaccination against Covid-19.”

New Covid symptoms recognised by the NHS

The new symptoms have been added to the NHS website, along with the three traditional symptoms of a fever, a new and persistent cough, and a loss or change in taste or smell.

According to the signs of Covid-19 that people should look out for also include:

 shortness of breath;
 feeling tired or exhausted;
 an aching body;
 a headache;
 a sore throat;
 a blocked or runny nose;
 loss of appetite;
 feeling sick or being sick.

A note on website adds: “The symptoms are very similar to symptoms of other illnesses, such as colds and flu.”