Covid-19 patients have immune system antibodies for at least two MONTHS after recovering from the virus, scientists find in a boost to hopes of long-term immunity and a working vaccine

People who have recovered from Covid-19 still have stable levels of antibodies for at least two months after their illness, a study has found.

Antibodies are substances in the immune system which the body uses to remember how to fight off an infection, and their presence usually means someone is immune.

Researchers at universities in the UK and a company developing an antibody test have found that these coronavirus antibodies seem to persist for at least two months.

Scientists are still unsure whether people can catch the disease more than once, which is one reason the public aren't being offered tests to work out if they've had it.

A successful vaccine will rely on long-lasting antibodies being produced by people's immune systems and the new finding is a ray of hope for vaccine development.

However, the study also found that some people who had been officially diagnosed with the virus did not develop any antibodies at all. People who only get a mild infection may not develop these, scientists have found.

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Scientists and a company developing an antibody test found that people with coronavirus antibodies were able to retain them in their blood for two months or more (Pictured: A blood test used to detect whether someone has had the virus in the past)

The research was done by researchers at St George's University in London and the Liverpool School of Tropical Medicine, along with the British testing company Mologic and the Institut Pasteur de Dakar, in Senegal.

It analysed results from antibody tests - blood tests to detect antibodies - carried out on 177 people who had been officially diagnosed with Covid-19. 

It found that in those patients who tested positive for antibodies, the level of them in the blood remained stable for the entire two-month study.

The study also found that patients with the most severe infections with the largest immune response were more likely to develop antibodies.

Scientists said the reason for this could be that those people were likely to be exposed to a larger amount of the virus and therefore to develop a larger amount of antibodies in response.  

They add that further mechanistic work is required to understand if and why this may be the case.

Professor Sanjeev Krishna, chief of the Molecular and Medical Parasitology Group at St George's, said: 'Our results provide an improved understanding of how best to use viral and antibody tests for coronavirus, especially when not every person exposed to the virus will have a positive response.

'We need to understand how best to interpret the results from these tests to control the spread of the virus, as well as identifying those who may be immune to the disease.

'With the number of infections in the UK going down, we now have the very welcome challenge of attempting to carry out more tests to understand whether other factors are associated with an immune response, such as viral load and genetic factors.

'We hope that by sharing our data at an early stage, this will accelerate progress towards effective use of test results around the world.'

Between two per cent and 8.5 per cent of people in the study did not appear to have any Covid-19 antibodies at all when they were, despite testing positive in the past. 

Professor Krishna and his colleagues said this could be because people develop different types of antibodies or immune responses.

Or it could be the case that antibodies are harder to detect in people who only had mild illnesses, because their immune systems won't have reacted as strongly.

The study also explored associations between different characteristics and antibody responses, which backs up the theory that worse illness leads to more antibodies.

Being of non-white ethnicity was associated with a higher antibody response, tying into the knowledge that patients from BAME backgrounds are more likely to develop severe disease.

Older patients and those with other conditions, such as with hypertension and being overweight were also more likely to have an antibody response.

The paper has not been reviewed by other scientists or published in a journal, but is online on medRxiv.