Why test students and staff who are asymptomatic for COVID-19?
Hear from our experts - Professor Chris Conlon (Chair Health Measures Advisory Group) and Professor Christopher Winearls, (Clinical Director Early Alert Service) - on the role of lateral flow device testing in a University setting
There are considerable grounds for optimism as Trinity term begins. Vaccine rollout in the UK has been impressive, with over half of the adult population having received at least one dose of the COVID-19 vaccine. The number of infections has fallen significantly in the past month and, importantly, hospital admissions and deaths due to COVID-19 have dramatically declined. Nevertheless, many people are still susceptible to infection with this coronavirus and we need to do all we can to reduce risks and minimise new infections.
Testing people with symptoms
Individuals with COVID-19 symptoms are highly infectious. The EAS (Early Alert Service) will test anyone who thinks they have symptoms with a laboratory polymerase chain reaction (PCR) assay, which is highly specific and sensitive. The PCR test is currently the gold standard. It checks for the genetic material (RNA) of the virus and gives a positive or negative result within 24 hours.
If a person receives a positive result, they must continue to isolate, staying away from other people for ten days from the onset of symptoms, and tell all the people they could have infected to do the same. These close contacts only need to be tested if they themselves develop symptoms of COVID-19. At any one time we can estimate the number of people in the University who are either infectious or potentially infectious. The EAS has been successful: in the last two terms we have identified 1,252 cases of COVID-19, 1,131 of whom were students and 121 staff.
This success stems from the actions of students and staff, who have come forward when symptomatic and isolated appropriately to reduce transmission. However, there has been some spread within the University and colleges, usually within households and, occasionally, because the rules have not been followed. To our knowledge two members of the University have, unfortunately, died from COVID-19 since the start of the pandemic in March 2020, underlining the seriousness of this disease.
Current estimates suggest that 30% of those currently infected with COVID-19 are asymptomatic; in many cases this is because these individuals have only recently been exposed to the virus. As we cannot be sure who and where these asymptomatic individuals are, it is crucial that everyone complies with all the recommended precautions in their interactions with others. These precautions are important not just within our own University environments, but also in the wider world, where most COVID-19 infections are acquired. The overall aim of these precautions is to reduce the transmission of COVID-19.
Can we identify those asymptomatic individuals who are unaware that they are infected with the virus? Theoretically we could do so by compulsorily testing everybody every day by PCR. However, this would be an impractical, unaffordable and socially unacceptable search for a few needles in what are many haystacks.
There is now a simple and cheap COVID-19 test called the Lateral Flow Device, or LFD. Unlike the PCR assay, LFDs do not detect the virus itself or its genetic material but, instead, detect viral proteins in a nasal and throat swab. Many students will be familiar with the LFD from the Christmas travel programme and from the availability of testing upon return to Oxford for Hilary term. If an LFD test returns a positive result it is 99.9% likely that the virus is present. Unfortunately, it will be negative in around 25% of people who are carrying the virus. This is because the LFD, unlike the PCR, does not amplify the viral components and will therefore not pick up those individuals with low levels of virus in their nose and throat.
Some of these will remain relatively low infection risks but others will, over the next few days, develop high levels of virus and become infectious; hence the need to repeat tests regularly. Testing everybody twice a week would identify 75% of the people who might unknowingly be capable of infecting others. Crucially, for this screening system to reduce transmission, we must maximise the number of people using LFDs. If only a third of students and staff were to engage with this system, we would miss the majority of the asymptomatic virus carriers.
We have conducted a pilot study of asymptomatic self-testing using LFDs in staff across a range of University environments. Testing was taken up by 500 individuals (> 70% of those eligible) in the first month and we detected two asymptomatic cases who then immediately self-isolated. This then avoided the risk of transmission at work. These asymptomatic individuals developed symptoms soon after their positive LFD results. The infections were subsequently confirmed by PCR. Those participating in the pilot reported feeling reassured by the asymptomatic testing programme and stated that it had increased their confidence in working in their University environments.
Assisted LFD Testing
The government has instructed universities to offer a programme of assisted testing for all students and staff. This replaces the self-testing system that we have used previously and will involve twice weekly attendance, with a booked appointment, at a conveniently placed testing centre. Each student or staff member attending will swab themselves and hand the sample in a tube to an assistant, who will run the LFD test for the individual. This will allow you to arrive, swab yourself, and leave the site within five minutes. The result of your LFD will then be communicated to you confidentially within a few hours. A negative result from your LFD has no implications and should not be interpreted as excluding COVID-19 infection. Routine preventive measures must continue to be followed. A positive LFD result will mandate immediate self-isolation and will trigger contact tracing in order to reduce transmission. A positive result should also be confirmed by booking an EAS PCR test. For those who are confirmed to be infected, there will be college and departmental support and welfare provision to allow for safe isolation.
Although this asymptomatic testing is voluntary, a high take-up rate will help identify those occasional people who are infectious. This will allow them to self-isolate with support and will reduce the risk of transmission to others. The success of this programme will allow a speedier return to normal life for all in the University.
This programme will provide an additional measure to further minimise both the transmission of the virus, and the disruption of the lives and work of our students and staff. The testing sites are at St Luke’s Chapel on the Radcliffe Observatory site on Woodstock Road, at the University Club on Mansfield Road, and at the Richard Doll Building on the Old Road Campus. We urge all members of the University to engage with this testing programme.
The government has just announced that all members of the public can get LFDs from NHS testing centres, from pharmacies or by post, so that they can do their own tests at home. For students and staff using this programme, we would urge them to report any positive results via EAS and to get a confirmatory PCR at one of the EAS testing pods.
The most important proven and effective measures to contain COVID-19 are:
- Abiding by the national guidance and adhering to COVID-19-secure measures in our workplace and in our community
- Regular asymptomatic testing for COVID-19
- Seeking a test if symptomatic
- Isolating if we test positive, or have been in close contact with someone who is
- Taking up the invitation to be vaccinated when offered.
Professor Chris Conlon (Chair, University Health Measures Advisory Group)
Professor Christopher Winearls (Clinical Director, University Early Alert Service)