Research and analysis

COVID-19: early release from self-isolation using LFD tests

Updated 18 May 2023

Applies to England

Main messages

Between 22 December 2021 and 24 February 2022, there were 6,922,949 positive cases of coronavirus (COVID-19) reported from antigen detecting lateral flow device (LFD) tests or polymerase chain reaction (PCR) tests for SARS-CoV-2.

At the time, people with positive test results were required to self-isolate for 10 days to reduce the risk of onwards transmission; however, this could be reduced to 5 full days days if 2 consecutive daily LFD tests returned a negative result. Over the 65-day period, 717,722 individuals were eligible for early release from self-isolation through this policy.

In total it is estimated that individuals regained 2,346,781 days of self-isolation or an average of 3.3 days per person through implementation of this policy.

The data in this release can be used to estimate the potential impact of the policy to reduce self-isolation length between 22 December 2021 and 24 February 2022.

This data should not be used to:

• calculate the prevalence of COVID-19 in the wider population
• calculate case positivity rates
• assess the effectiveness of the testing types used in England
• compare the mass testing programmes across nations

This report does not include tests conducted and reported by residents in private or public sector institutions as they were subject to different guidelines.

Introduction

During the COVID-19 pandemic, people who tested positive for COVID-19 were asked to self-isolate for 10 days to prevent onward transmission of the disease to others.

On 22 December 2021, following public health advice based on modelling of the impact of reducing the self-isolation period, the self-isolation period could be reduced from 10 days to 6 full days if 2 antigen LFD tests, taken 24 hours apart starting on day 6, returned negative results.

On 17 January 2022, after careful consideration of modelling (1, 2) from the UK Health Security Agency (UKHSA), this was reduced in England to 5 full days following 2 consecutive day negative LFD results from day 5.

Studies have shown that LFDs are most likely to give positive results during the infectious period of the COVID-19 infection cycle (3, 4), that is, the period when an infected person has the potential to transmit the virus to others, and that LFDs reliably detect the end of the infectious period by returning a negative result. LFDs can thus be used to identify when the isolation period should end (2).

Modelling (1) had shown that combining LFD testing with self-isolation had the potential to reduce the proportion of individuals who were still infectious when released from isolation as well as reducing the time spent in isolation by those who were no longer infectious.

It was estimated (2) that if individuals self-isolated for the full 10 days, about 5% would remain infectious upon release. However, the average excess isolation per person would be 142 hours. If, instead, isolation was changed to 10 days or 2 negative LFD tests from day 6, 6% of those released from isolation would still be infectious and the excess isolation per individual would drop to 82 hours. Thus, this change in policy came at minimal cost in terms of the release of infectious individuals into the community but delivered a large reduction in excess isolation.

UKHSA modelling showed that the proportion of individuals released while infectious would rise to about 7% once guidance was changed to end isolation on day 6 with 2 consecutive negative LFD results from day 5 (see Self-isolation for those with COVID-19 can end after 5 full days following 2 negative LFD tests (withdrawn) for more details).

Individuals were only supposed to leave isolation once they had had a negative LFD test on 2 consecutive days; if they tested positive on day 5, 6 or 7, they had to continue testing until they had 2 negative tests. A single negative LFD was not considered sufficient to end isolation due to the risk of a false negative result since modelling showed that 10-day self-isolation or a single LFD negative test from day 7 would mean that 9% of individuals released from isolation would still be infectious, which was considered too much of an increase to implement as policy.

It was therefore required that 2 negative lateral flow tests were taken on consecutive days and reported prior to release from self-isolation sooner than the full 10-day period. The first test had to be taken no earlier than day 5 of the self-isolation period, and the second had to be taken the following day. If an individual was positive on day 5, then a negative test was required on day 6 and day 7 in order to be released from isolation on day 7. If the individual tested positive on day 6, then a negative test was required on days 7 and 8, and so on, following the same pattern until the end of day 10.

The modelling estimated that as an alternative to a blanket self-isolation policy of 10 days, 2 negative LFD tests on consecutive days from day 6 could reduce excess isolation per person from 142 hours to 82 hours, thus saving each individual released early from self-isolation an average of 60 hours.

Existing public health measures remained in place, including:

• staying at home if you felt unwell
• getting a PCR test if you experienced any COVID-19 symptoms
• wearing a face covering in crowded, enclosed spaces
• working from home if possible
• maintaining social distancing and regular hand washing
• taking up the offer of the free COVID-19 vaccination

Self-isolation was continued in certain circumstances, such as for those who worked with vulnerable people.

Methodology

This data contains tests reported through the pillar 2 testing routes only (swab testing the wider population) between 22 December 2021 and 24 February 2022 which was the entire timespan of this policy being in place.

This data includes those reported through the existing National Testing Programme digital infrastructure and does not include tests that were not reported via this route.

Data associated with an episode is based on the first positive LFD or PCR test within a 13-week rolling window, then each of the first LFD tests taken on days 5 to 10 (inclusive) is matched to the day 0 test.

The tests are linked using multiple pieces of personal information such as name, date of birth, and NHS number.

Results

Between 22 December 2021 to 24 February 2022, 6,922,949 positive cases of COVID-19 were reported through testing with either an antigen-detecting LFD or PCR test kit.

Between 22 December 2021 and 16 January 2022, 3,894,986 people reported a positive test result, of which 306,806 (8%) were eligible for early release (day 7).

Between 17 January 2022 and 24 February 2022, 3,027,963 people reported a positive test result, of which 410,916 (14%) were eligible for early release (day 6).

In the 65 days the policy was live, 717,722 (10%) people were eligible for early release out of the 6,922,949 positive tests reported.

Table 1 shows the total number of positive cases and when they were eligible for release from isolation.

Table 1. Number of individuals eligible for early release from self-isolation between 22 December 2021 and 24 February 2022

Month	Day 0 positive	Day 6 release	Day 7 release	Day 8 release	Day 9 release	Day 10 release
December 2021	1,683,578		48,219	34,484	24,732	16,874
January 2022	3,959,979	84,075	128,584	95,185	75,120	50,703
February 2022	1,279,392	52,793	35,867	30,101	24,185	16,800
Total	6,922,949	136,868	212,670	159,770	124,037	84,377

When results were broken down by age, they showed that 193,294 people of school age (18 and under) were eligible for early release, and 479,348 people of working age (19 to 64) were eligible for early release under this policy. For the full age breakdown see the Appendix.

Days released from self-isolation were counted as follows: those released on day 10 regained one day; those released on day 9 regained 2 days; and so on up to those released on day 6 who regained 5 days. Days were counted as whole days as it was not possible to know what time of day tests were taken to be able to count in hours. In total, 2,346,781 days of self-isolation were regained. On average, each individual who was released early from self-isolation regained 3.3 days.

Discussion

The introduction of this policy kept the effectiveness of self-isolation in breaking chains of transmission while reducing the burden of isolation on the general public. Due to this policy, 717,722 individuals were able to leave self-isolation at some point from day 6 onwards after 2 negative LFD tests instead of observing a full 10 days of self-isolation.

Although the time when an individual took their second LFD test was not known, if it were assumed they tested first thing in the morning, then, on average, each individual released early reduced their self-isolation period by 3.3 days. In total, this equates to 2,346,781 days saved from self-isolation.

There were 479,348 individuals aged 19 to 64 and 193,294 individuals aged 18 and under who were released early from self-isolation under the policy. Assuming the 3 days saved from self-isolation fell on working days, and that all the individuals under 18 were in full time education, it is possible that 1.4 million work days and 579,000 school days were saved in this way.

Average daily earnings for an individual in Great Britain stand at £125, meaning individuals had the potential to earn £375 each from early release (see Average weekly earnings in Great Britain from the Office of National Statistics).

A missed day of school leads to a permanent education loss of a little under one day, which is likely to reduce lifetime earnings by around 0.05% (see Education recovery and resilience in England: phase 2 report from the Education Policy Institute). This equates to a potential loss in future earnings of between £300 to £700 per day of school missed using plausible ranges for lifetime earnings (see Education recovery and resilience in England: phase 2 report). Enabling early release from isolation by using LFDs potentially averted this loss of earnings for 193,294 young people.

The result presented here of 717,722 people who were eligible for early release from self-isolation is likely to be an under-estimate. Firstly, not all individuals who tested to release from self-isolation will have registered their LFD tests. Secondly, the matching process through which LFD results were linked to the same individual used a strict criteria which means that where identifiers did not match exactly it was not possible to link the data. For example, if an individual entered their full first name for one test and their nickname for the second test they would not have been matched. Therefore, the potential impact of this policy is higher than that stated in this report.

Appendix

Early release results broken down by age group. There were 21,010 individuals eligible for early release for whom there was no age information.

Table 2. Number of individuals aged 16 and under eligible for early release from self-isolation between 22 December 2021 and 24 February 2022

Month	Day 0 positive	Day 6 release	Day 7 release	Day 8 release	Day 9 release	Day 10 release
December 2021	178,203		4,899	2,960	1,970	1,184
January 2022	1,071,084	37,536	38,411	28,122	21,666	11,808
February 2022	241,956	14,098	6,930	5,209	3,430	1,619
Total	1,491,243	51,634	50,240	36,291	27,066	14,611

Table 3. Number of individuals aged 17 to 18 eligible for early release from self-isolation between 22 December 2021 and 24 February 2022

Month	Day 0 positive	Day 6 release	Day 7 release	Day 8 release	Day 9 release	Day 10 release
December 2021	44,717		1,174	719	422	218
January 2022	96,562	1,650	2,868	1,682	1,082	600
February 2022	28,580	1,278	707	554	331	167
Total	169,859	2,928	4,749	2,955	1,835	985

Table 4. Number of individuals aged 19 to 24 eligible for early release from self-isolation between 22 December 2021 and 24 February 2022

Month	Day 0 positive	Day 6 release	Day 7 release	Day 8 release	Day 9 release	Day 10 release
December 2021	201,937		5,180	3,336	2,049	1,174
January 2022	309,071	4,110	8,550	5,313	3,607	2,356
February 2022	96,155	3,897	2,439	1,812	1,312	822
Total	607,163	8,007	16,169	10,461	6,968	4,352

Table 5. Number of individuals aged 25 to 64 eligible for early release from self-isolation between 22 December 2021 and 24 February 2022

Month	Day 0 positive	Day 6 release	Day 7 release	Day 8 release	Day 9 release	Day 10 release
December 2021	1,125,972		34,380	25,062	18,199	12,521
January 2022	2,213,906	38,071	72,641	54,914	44,024	31,912
February 2022	785,410	30,253	22,924	19,880	16,590	12,020
Total	4,125,288	68,324	129,945	99,856	78,813	56,453

Table 6. Number of individuals aged 65 and over eligible for early release from self-isolation between 22 December 2021 and 24 February 2022

Month	Day 0 positive	Day 6 release	Day 7 release	Day 8 release	Day 9 release	Day 10 release
December 2021	122,644		2,474	2,323	2,045	1,743
January 2022	242,837	2,390	5,716	4,847	4,507	3,874
February 2022	120,671	3,106	2,777	2,566	2,467	2,144
Total	486,152	5,496	10,967	9,736	9,019	7,761

This UKHSA report was prepared by:

• Olumide Kolade
• Joanna Cole-Hamilton
• Fergus Cumming
• Sarah Tunkel
• Tom Fowler

References

1. Bays D, Whiteley T, Williams H, Finnie T, and Gent N. ‘Mitigating isolation: further comparing the effect of LFD testing for early release from self-isolation for COVID-19 cases’ medRxiv (preprint) 2022

2. Bays D, Whitely T, Pindar M, Taylor J, Walker B, Williams H, Finnie T, and Gent N. ‘Mitigating isolation: The use of rapid antigen testing to reduce the impact of self-isolation periods’ medRxiv (preprint) 2021

3. Hakki S, Zhou J, Jonnerby J, Singanayagam A, Barnett JL, Madon KJ and others. ‘Onset and window of SARS-CoV-2 infectiousness and temporal correlation with symptom onset: a prospective, longitudinal, community cohort study’ Lancet Respiratory Medicine 2022: volume 10, issue 11, pages 1,061 to 1,073

4. Pickering S, Batra R, Merrick B, Snell LB, Nebbia G, Douthwaite S, and others. ‘Comparative performance of SARS-CoV-2 lateral flow antigen tests and association with detection of infectious virus in clinical specimens: a single-centre laboratory evaluation study’ Lancet Microbe 2021: volume 2, issue 9, pages e461 to e471