People infected with Covid-19 have an increased risk of death 18 months after infection, according to a new study co-led by University College London and the University of Hong Kong.

Researchers found that Covid-19 patients were 18 times more likely to die in the first three weeks after infection and five times more likely to die after 18 months than people who had not been infected by the disease.

Those infected by Covid-19 were also more likely to develop cardiovascular disease.

The findings, published in Cardiovascular Research, indicate that people infected with Covid-19 should be monitored for at least a year to highlight cardiovascular risks resulting from infection.

Using data from the UK Biobank, the researchers identified a cohort of more than 7500 patients who had been infected with Covid-19 between March 2020 and November 2020, before the release of vaccines in the UK. The cohort was followed for up to 18 months until August 2021.

Each infected case was randomly matched with up to ten participants who had not been infected with Covid-19 and were the same age (within five years) and the same sex. The nearly 160 000 unvaccinated participants were made up of two cohorts. One was a historical cohort from before the pandemic, with data collected between March 2018 and November 2018. The second was a contemporary cohort from between March 2020 and November 2020. Most participants from all cohorts were in their 60s.

For each participant, the researchers identified evidence of cardiovascular disease, including heart failure, stroke and coronary heart disease, and cardiovascular conditions, including stroke, atrial fibrillation and myocardial infarction. They also identified where death had occurred from cardiovascular disease for both the acute phase of infection (within 21 days of diagnosis) and the post-acute phase which continues up to 18 months. Patients with a history of cardiovascular disease or conditions were excluded from the analysis.

Compared with the two uninfected cohorts, patients with Covid-19 were approximately four times more likely to develop major cardiovascular disease in the acute phase and 40% more likely in the post-acute phase. Myocardial infarction, coronary heart disease, heart failure, and deep vein thrombosis were commonly seen. The risks of some cardiovascular conditions such as strokes and atrial fibrillation were elevated in infected patients in the short term but then returned to normal levels in the longer term.

Study author Professor Ian Wong from University College London said: ‘Covid-19 patients were more likely to develop numerous cardiovascular conditions compared to uninfected participants, which may have contributed to their higher risks of death.’

‘The historical control cohort was included to rule out the effect of routine healthcare services being reduced or cancelled during the pandemic, which led to worsening health and increased mortality even in uninfected people.’

The researchers also found that patients with severe Covid-19 were more likely to develop major cardiovascular disease or die than non-severe cases.

Professor Wong added: ‘The findings indicate that patients with Covid-19 should be monitored for at least a year after recovering from the acute illness to diagnose cardiovascular complications of the infection, which form part of long Covid.’

The study was undertaken during the first wave of the pandemic, and the researchers hope that future work will evaluate subsequent outbreaks and the impact of vaccinations.