Recovered COVID-19 patients could help provide 'shield immunity', study claims

People who have caught COVID-19 and recovered from the disease could be encouraged to rejoin the general public to provide 'shield immunity'.

The reintroduction of recovered coronavirus patients would, in theory, help reduce the rate of transmission of SARS-CoV-2, the virus which causes COVID-19. 

Researchers from Georgia Institute of Technology say the immunity of the recovered patients would help to slow the spread of the contagion.  

Ushering out more recovered patients would ensure most interactions include an immune person, which makes it impossible for the virus to propagate. 

This so-called 'shield immunity' strategy could help quash the R0 — the amount of people an infected person passed the virus on to — and could be used in conjunction with existing precautions, such as social distancing, contact tracing and self-isolation. 

Immune individuals could play a key role in getting society back to a normal level of functionality while also helping fight the pandemic, scientists claim.

Shield immunity is a different concept to herd immunity and is designed to reduce interactions that would pass on the virus. 

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People who caught COVID-19 and recovered from the disease could be encouraged to take up roles on the coronavirus frontline to provide 'shield immunity' (file photo)

People who caught COVID-19 and recovered from the disease could be encouraged to take up roles on the coronavirus frontline to provide 'shield immunity' (file photo)

The reintroduction of the recovered coronavirus patients would, in theory, help reduce the rate of transmission of SARS-CoV-2, the virus which causes COVID-19. Researchers from Georgia Institute of Technology say the immunity of the recovered patients could be utilised to slow the spread of the contagion

The reintroduction of the recovered coronavirus patients would, in theory, help reduce the rate of transmission of SARS-CoV-2, the virus which causes COVID-19. Researchers from Georgia Institute of Technology say the immunity of the recovered patients could be utilised to slow the spread of the contagion

The study's findings are based on a trove of assumptions, which scientists are currently unable to guarantee. 

For example, the study is only valid if recovered people are absolutely virus negative, produce antibodies to defend them against SARS-CoV-2, and are able to interact safely with both susceptible and infectious people.

It also relies on immunity lasting for more than a year and 100 per cent accurate antibody testing kits being available to all. Currently, scientists are unable to guarantee any of these things. 

Scientists modified an existing piece of modelling software to see what would happen if uninfected people were replaced in society with immune individuals. 

'Shield immunity' was tested on a model population of ten million people under two scenarios: one with a high rate of transmission (R0=2.33) and one with a low rate of transmission (R0=1.57). 

Two forms of shielding were tested, intermediate and advanced, according to the study. 

In the high-transmission scenario, 71,000 deaths were predicted if the R0 was not altered. However, this dropped to 58,000 and 20,000 deaths under intermediate and advanced shielding, respectively. 

Herd immunity compared to shield immunity  

 HERD IMMUNITY

Is the goal of vaccination programmes 

Requires majority of the population to be infected at some point 

 A person who has not developed immunity could still catch the disease 

The likelihood is very slim as the virus spread is halted 

The virus cannot spread among the immune individuals so R0 is extremely low and the virus is starved of viable hosts 

This means at-risk groups who cannot receive vaccines are still afforded protection 

 SHIELD IMMUNITY 

Is used to help quash the R0 of a disease 

Works with only a small percentage of people infected 

Recovered people are immune, unable to contract the disease again or pass it on 

The objective of a shield immunity strategy is to use immune individuals on the frontline 

They will be able to keep essential services such as hospitals and pharmacies functioning while reducing the probability of transmission 

Herd immunity is the goal for vaccination programmes but is not the goal for coronavirus as it would result in enormous loss of life

Pictured, a diagram showing how a recovered person (blue) carries to reduce viral transmission. Those people would be returned to society and would be the main interactors (top box). Their interaction with either infected people (green) or vulnerable people (orange) does not result in the propagation of infection. This is in contrast to interactions in which either infected people (bottom) or vulnerable people (middle) are the main interactors

The difference between herd immunity (left) and shield immunity (right). Shield immunity refers to using those with immunity to act as a buffer and ensure the vulnerable and infected are protected. Herd immunity occurs at a later date and requires far more people to catch the virus for it to take effect

In the low-transmission scenario, the predicted death toll was 50,000 and this dropped to 34,000 and 8,400 when shielding was implemented. 

Values for the R0 vary wildly, but it is believed the UK's current R0 is around 0.7.  

Shield immunity is different to herd immunity, the concept which hit headlines last month. 

Shield immunity refers to using those with immunity to act as a buffer and ensure the vulnerable and infected are protected. 

'The objective of a shield immunity strategy is to help to sustain the interactions necessary for the functioning of essential goods and services while reducing the probability of transmission', the researchers write in their study.

Herd immunity occurs at a later date and requires far more people to catch the virus for it to take effect. 

It is an effective 'safety in numbers' approach which occurs when so many people already have immunity to the disease that it effectively stops spreading. 

Professor Joshua Weit, who led the study, explained on

: 'Unlike herd immunity (which would lead to disastrous consequences given the severity of COVID-19), the intent of shield immunity is to dilute transmissable interactions intentionally through elevating interactions with recovered, rather than depletion of susceptibles.' 

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Antibody tests could tell recovered, and therefore immune, COVID-19 patients and this would give them the all-clear to resume roles in society. these test would need to be 100 per cent accurate, which is currently not a possibility

Antibody tests could tell recovered, and therefore immune, COVID-19 patients and this would give them the all-clear to resume roles in society. these test would need to be 100 per cent accurate, which is currently not a possibility 

Scientists modified an existing piece of modelling software to see what would happen if uninfected people were replaced in society with immune individuals. They found utilising the shield immunity strategy could save tens of thousands of  lives

Scientists modified an existing piece of modelling software to see what would happen if uninfected people were replaced in society with immune individuals. They found utilising the shield immunity strategy could save tens

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