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Results from our animal free research could be a game changer in the fight against Covid-19

Published on January 14, 2022

Animal Free Research UK funded scientists Professor Lorna Harries and Summer School protégé Merlin Davies from our ARC 2.0 at the University of Exeter explain how they created a PCR test that identifies if someone is still infectious with Covid-19.

During the drastic measures introduced in early 2020 to curb the Covid-19 pandemic, our clinical colleagues noticed high levels of infection despite the public’s careful adherence to the isolation rules and guidelines.

We knew back then the conventional PCR and lateral flow tests (we have all become so familiar) with could show a positive result long after an individual had stopped being infectious – so we wanted a better way to identify who is still infectious from who is not.

Thanks to its generous supporters, the funding we received from Animal Free Research UK allowed us to examine how PCR testing identifies a part of the Covid-19 virus genome that is only present when the virus is actively dividing.

We adapted the PCR test and removed any animal components – including the standard molecular tests which sometimes contain proteins from cow serum to make the reactions more stable – and we changed the reaction conditions so as to enable our clinical colleagues to run it alongside their conventional PCRs.

We then put the modified, human relevant test to use to see how long people infected with Covid-19 remain infectious.  We took a collection of samples collected from our local Covid-19 patients as part of their routine clinical care, and measured the amount of active virus present in each sample.

We then related these measurements to the clinical characteristics of the patients, including the time from the start of symptoms to their last positive test; their age, sex and weight, and the presence of any underlying conditions or medicines that would suppress the immune system.

What we found somewhat shocked us.

Whilst most people clear the virus within 10 days, about 1 in 10 still have levels of active Covid-19 virus that could potentially lead to an infection in an exposed person.

After a 7-day isolation period it was 1 in 5, and after only 5 days it was 1 in 3 people. Furthermore, we couldn’t tell who these people were from their clinical characteristics.

All of this research was carried out on the original strain of Covid-19 which first established a foothold in the UK.  The current strains – Delta and Omicron – are more infectious, so the amount of virus needed to infect someone else could well be lower, and those numbers of infectious people could be higher.

We may all agree that it is necessary to balance the need to stop onward transmission but desire to keep the country running, so there is real pressure to cut the isolation period to a minimum.

Government guidance initially ordered those who tested positive to isolate for 10 days, and more recently this was reduced to 7 days – and at the time of writing there is now official discussion about whether to allow a further reduction to 5 days.

Our findings suggest that it if the proposed changes to once more cut the isolation period, it is very important for people to have two negative lateral flow tests 24hrs apart before re-entering society.

It is also strongly advised everyone gets vaccinated, since vaccination is known to reduce the transmissibility of the virus.

Crucially, our results also show where the consequences of onward transmission would be a real issue, such as in a care home setting, where there are frail, older people who may have waning vaccine immunity, underscoring how necessary it is to be extra careful. So our adapted PCR test could be useful in making sure Covid-19 is not, for example, introduced when someone is returning to a care home after having been in environments with a high risk of transmission such as hospitals and doctors’ surgeries.

Merlin and I are extremely grateful to Animal Free Research UK – and especially to you, the charity’s supporters for funding this important research.

In these exceptional, uncertain times, what is assured is that every one of us can make a difference – either by undertaking a kinder and more human relevant science, or by funding it.


Written by Professor Lorna Harries and Merlin Davies of the University of Exeter.


The paper is entitled ‘Persistence of clinically-relevant levels of SARS-CoV2 envelope gene subgenomic RNAs in non-immunocompromised individuals’, and is published in the international Journal of Infectious Diseases.




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