COVID-19 linked with wider set of symptoms than previously thought – REACT study


A COVID testing site

A study of over a million people in England has revealed a range of symptoms that are linked with having the coronavirus.

Of these symptoms, seven were found to be best predictors of having COVID-19 among symptomatic individuals and could therefore improve case detection if included in testing criteria.

In addition to the symptoms used to identify who is eligible for a PCR test in England (fever, new continuous cough, loss or change to sense of smell or taste) –– a wide range of other symptoms were associated with COVID-19. However, around 60% of infected people did not report any symptoms in the week leading up to their test.

Swab tests and questionnaires collected between June 2020 and January 2021 as part of the Imperial College London-led REACT-1 study showed that in addition to the symptoms above, chills, loss of appetite, headache and muscle aches were together most strongly linked with being infected. Having any of these either alone or in combination, was associated with higher risk of infection with the coronavirus and the more symptoms people showed the more likely they were to test positive.

Implications for COVID-19 testing

"I hope that our findings mean that the testing programme can take advantage of the most up-to-date evidence, helping to identify more infected people.” Prof Paul Elliott School of Public Health

People in England are currently encouraged to take a COVID-19 PCR test if they have at least one of the following symptoms: fever, new continuous cough, loss or change of sense of smell or taste. This is part of ‘Pillar 2 testing’. Based on these findings, the researchers estimate that current Pillar 2 PCR testing would pick up around half of all symptomatic infections if everyone eligible were tested. But if the additional symptoms were included, this could be improved to three-quarters of symptomatic infections.

Professor Paul Elliott, director of the REACT programme at Imperial, said: “These findings suggest many people with COVID-19 won't be getting tested – and therefore won't be self-isolating – because their symptoms don’t match those used in current public health guidance to help identify infected people.

"We understand that there is a need for clear testing criteria, and that including lots of symptoms which are commonly found in other illnesses like seasonal flu could risk people self-isolating unnecessarily. I hope that our findings on the most informative symptoms mean that the testing programme can take advantage of the available evidence, helping to optimise the detection of infected people.”

These findings are from the ongoing REal-time Assessment of Community Transmission (REACT-1) programme, led by Imperial and carried out in partnership with Ipsos MORI, and funded by the Department of Health and Social Care. They have been published in PLOS Medicine. Read the pre-print report

Symptoms for the alpha variant

The research also explored whether the emergence of the alpha variant (B.1.1.7, first identified in Kent) was linked with a different profile of symptoms.

"As the epidemic progresses and new variants emerge, it’s essential that we keep monitoring how the virus affects people so that testing programmes meet changing needs." Dr Joshua Elliott School of Public Health

Comparing self-reported symptoms in participants infected by the ‘wild type’ (the first identified novel coronavirus) and those by the alpha variant, showed that the symptoms that are predictive of alpha variant infection were broadly similar to those predictive of the wild type infection. Nevertheless, in keeping with findings from ONS, new persistent cough and sore throat were more predictive of B.1.1.7 infection and loss or change of sense of smell was more predictive of the wild type.

“As the epidemic progresses and new variants emerge, it’s essential that we keep monitoring how the virus affects people so that testing programmes meet changing needs," said Dr Joshua Elliott, from Imperial College London’s School of Public Health.

"We hope that our data will help inform testing guidance and the development of systems which could help better identify people who should take a COVID-19 test based on their symptoms.”

About the REACT programme

The REACT-1 study is monitoring current coronavirus infections in the community by testing around 100,000 randomly-selected people each month over a two-week period. The study recruits new people each month to help ensure the sample represents the wider population and offers a high-resolution snapshot of the situation across a particular time period. This is different from the ONS COVID-19 Infection Survey which runs continuously and samples the same people over time to understand household transmission.

People who volunteer for REACT-1 take throat and nose swabs at home, which are then analysed in a laboratory by a technique called RT-PCR. They also fill out a questionnaire detailing any symptoms they may have and providing information about social and demographic factors, such as where they work. These findings are helping guide public health measures so that the Government can better respond to the pandemic as the situation evolves.


Justine Alford

Justine Alford
Institute of Global Health Innovation

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