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Public healthJan 13, 2021

Healthcare workers praised for taking part in long-term national Covid-19 immunity study

Being infected with Covid-19 appears to offer people protection from further infection for several months, a Public Health England (PHE) study suggests.

The finding comes with an important caveat, however: those with immunity could still carry the virus in their noses and throats, meaning they could potentially pass it on.

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The public are reminded by PHE to stay at home to reduce transmission rates

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In the PHE study, more than 20,000 healthcare workers in 102 trusts in various parts of the UK have been tested for new Covid-19 infections since last June. The tests also check the presence of antibodies (which suggest people have been infected before).

At this stage of its evolution, the Siren (SARS-CoV-2 Immunity and Reinfection EvaluatioN) study offers no evidence on antibody or other immune responses linked to Covid-19 vaccines. The Siren study will consider vaccine responses later this year, PHE noted.

But those running the study have concluded that immunity acquired naturally as a result of past infections provides an 83 per cent protection rate against reinfection, in comparison to people who have never had the disease.

Immunity appears to last for at least five months

This protection apparently lasts for at least five months from when the person first becomes sick. This means that people who contracted Covid-19 in the first wave may now be vulnerable to catching it again, and only time – and more research – will reveal whether protection could extend beyond the five-month period.

During a period from 18 June to 24 November 2020, scientists detected 44 potential reinfections (two labelled ‘probable’ and 42 ‘possible’) out of a total of 6,614 participants who had tested positive for antibodies. This equates to an 83 per cent rate of protection from reinfection.

PHE also warned that although having antibodies offers some protection from becoming ill with Covid-19, early evidence from the next stage of the study suggests that some of those to whom this applies carry high levels of virus, which they could continue to transmit to others.

In a message to the general public, PHE stressed that everyone should continue to follow the rules and stay at home, even if they have previously had Covid-19, to prevent spreading it.

Praise for participating in study

We are immensely grateful to our colleagues in the NHS for giving up their time to volunteer, and whose continued participation at a time of great stress is making this research possible [Susan Hopkins, PHE]

Susan Hopkins, a PHE senior medical adviser who is leading the SIREN study, praised the NHS staff who contributed to the study: ‘We are immensely grateful to our colleagues in the NHS for giving up their time to volunteer, and whose continued participation at a time of great stress is making this research possible.’

Professor Hopkins added: ‘We now know that most of those who have had the virus, and developed antibodies, are protected from reinfection, but this is not total, and we do not yet know how long protection lasts. Crucially, we believe people may still be able to pass the virus on.

‘This means even if you believe you already had the disease and are protected, you can be reassured it is highly unlikely you will develop severe infections but there is still a risk that you could acquire an infection and transmit to others.’

To access a full version of the interim findings, visit: file:///Users/ian/Downloads/SIREN%20Interim%20analysis%20paper%20(1).pdf


Author: Ian A McMillan
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