Around half of nearly 1,000 key workers who self-reported symptoms of Covid-19 did not test positive for antibodies to the disease, according to research.
The study, from Public Health England (PHE), includes police, fire and healthcare workers and was conducted in June.
The researchers say their findings, which are yet to be peer-reviewed, suggest the symptoms were due to other conditions.
Ranya Mulchandani, a field epidemiology training programme fellow at Public Health England and the study’s lead author, said: “Although these findings are still subject to peer review, it is possible that a large number of people in the general population incorrectly believe that they have already had Covid-19.
“It is crucial that people do not get complacent and continue to observe government health advice, including social distancing and good hand hygiene, even if they think they have been infected in the past.”
The experts led by Ms Mulchandani studied three key worker groups at six acute NHS hospitals and two police and fire and rescue sites across England.
It is possible that a large number of people in the general population incorrectly believe that they have already had Covid-19
The third group, which was the control group in the cohort, included healthcare workers who had previously had a positive test for Covid-19.
The team collected information on the self-reported signs and symptoms of Covid-19 and compared this with the results from two antibody tests.
Out of 2,847 participants, 943 (33%) said they believe they had had Covid-19 based on their symptoms.
However, the researchers found that 466 (49%) of the 943 individuals tested negative on antibodies, suggesting “it is very unlikely they had had Covid-19”.
Those testing negative had significantly earlier dates of symptom onset, shorter illness duration, and a much lower reporting frequency of the loss of taste and smell compared to individuals with antibodies, the team said.
Ms Mulchandani said: “In the course of this study, we tested just under a thousand people who thought they had had Covid-19 due to compatible symptoms.
“We found that half of them lacked any evidence of having had the infection, testing negative for the presence of antibodies.”
The findings were presented at the European Society of Clinical Microbiology and Infectious Diseases Conference on Coronavirus Disease (ECCVID).