How many people who test positive for COVID-19 have no symptoms?
Various media sources have reported that about 8 in 10 people who test positive for COVID-19 have no symptoms. This follows results from the largest cross-sectional survey of the general population being carried out in England. The REACT-1 study has been sending viral testing kits and online questionnaires to over 120,000 people each month.
In May, 0.13% of 121,000 samples tested positive. In June, 0.08% of 160,000 samples tested positive. In both months, 70-80% of those testing positive had no symptoms in the past seven days.
The nasal and throat swabs only tell whether the person is carrying the COVID-19 virus at the time of testing – they cannot inform whether they’ve had it in the past. Although there may be practical difficulties in taking the swab sample, the results suggest that the current prevalence of COVID-19 in the community is very low and appears to be declining. The important thing is that the infection rate continues to fall and we do not experience a resurgence of cases.
Therefore the fact that many people with COVID appear to be asymptomatic and could transmit the infection without knowing it, highlights the need to continue to follow infection control measures.
Where did the story come from?
The REACT-1 study (Real-time Assessment of Community Transmission) has been commissioned by the Department of Health and Social Care (DHSC) and is being conducted by Imperial College London in collaboration with Ipsos MORI. DHSC has published two reports covering the preliminary results of REACT-1 from May and June.
What is the basis for the claim?
REACT-1 is recruiting a sample of the population in England to do a home test for COVID-19. The test involves taking a swab from the nose and throat to see whether they are currently carrying the virus. Participants are asked to complete an online questionnaire. This covers their age, gender, ethnicity, socioeconomic background, medical health, and a range of other questions on symptoms, contacts and daily activities in the past 7 days, including use of shops, public transport, pubs, eateries and leisure facilities.
Main results for May 2020:
- 120,610 swabs were returned and 159 – 0.13% – were positive
- 69% of those testing positive reported no symptoms in the past 7 days
- The R-rate (number of secondary infections resulting from one infected person) was estimated at 0.57
- Key workers were most likely to test positive – 0.71% of care workers, 0.47% of healthcare workers, 0.17% of other key workers
- Other factors associated with a higher chance of testing positive: recent contact with a suspected case, Asian ethnicity and younger age (18-24) group
Main results for June 2020:
- 159,199 swabs were returned and 123 – 0.077% – were positive
- 81% of those testing positive reported no symptoms in the past 7 days
- The R-rate was 0.58 – essentially the same as May
- There was no longer a difference in prevalence between key workers and other people
- Factors associated with a higher chance of testing positive: recent contact with a suspected case, Asian, Black and other ethnicities, but no difference by age group
This study cannot inform COVID prevalence among higher risk settings, such as in hospitals or residential homes, where it may be higher. But in the general community, the prevalence of the virus appears to be low and declining.
However, both the high rate of asymptomatic carriage and the fact that the transmission rate has remained much the same for May and June, highlight the need to avoid complacency. Infection rates could fluctuate by the month, and we do not know that July or August is automatically going to follow the same downward trend.
We need to continue to follow government recommendations around social distancing, hand sanitisation and use of face masks to ensure that infection rates do not start to rise again, particularly as we go into the autumn and winter flu season.
What do trusted sources say?
In a government press release, Health and Social Care Secretary Matt Hancock was quoted: “This research highlights how, thanks to everyone’s efforts and sacrifice, alongside targeted measures to counter the spread of this virus in health and care settings, we were able to keep rates of infection low as some restrictions were lifted.”
However, he continued that people should still self-isolate if they experience any symptoms, seek testing and provide their details to NHS Test and Trace so that the virus can be kept under control.
Analysis by EIU Healthcare, supported by Reckitt Benckiser
- Imperial College London. Real-time Assessment of Community Transmission (REACT) Study (Accessed 10 August 2020)
- Department of Health and Social Care. REACT-1: Real-time assessment of community transmission of coronavirus (COVID-19) in May 2020. (Published 15 July 2020)
- Department of Health and Social Care. REACT-1: Real-time assessment of community transmission of coronavirus (COVID-19) in June 2020. (Published 6 August 2020)