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Signs of immunity disappear rapidly in severely ill coronavirus patients in less than a month after they are discharged from the hospital, according to a study.
Researchers looking for antibodies, substances in the blood that build immunity against the virus, have found that they decrease dramatically once the patient recovers.
The finding is concerning news for the hope that people will become immune to Covid-19 after having it for the first time.
Most of the people who were sent home from the hospital after having the illness showed signs of antibodies, suggesting that their bodies had learned to protect themselves from the virus, but were not strong.
About 81 percent of the patients had the antibodies, the Chinese study found, but only a “small portion” of them had any with the ability to neutralize or kill the virus.
It remains a mystery whether people become immune to Covid-19 after having it.
There are signs that the body is learning to defend itself, but there are also a growing number of “credible” cases in which people are reinfected.
If the body cannot retain antibodies long term, it could mean that a vaccine cannot offer permanent protection, as scientists and politicians around the world hope.
Scientists monitored 19 non-severe and seven severe Covid-19 patients for one month and three weeks to determine how their bodies produced antibodies (stock image)
Scientists at Nanjing University School of Medicine in China monitored 19 non-severe and seven seriously ill Covid-19 patients for one month and three weeks to determine the progression of their antibody response.
They found that patients had a variable level of antibody responses, with only a “small portion” developing a potent level of neutralizing activity. The scientists did not say exactly how many people had this.
The study indicates that three to four weeks after hospital discharge, the neutralizing activity of the antibodies of recovered patients decreased significantly.
The authors wrote: ‘The world is facing an unprecedented challenge with communities and economies affected by the growing coronavirus disease 2019 (Covid-19) pandemic …
‘The development of the antibody response to Sars-CoV-2, the virus that causes Covid-19, began to be reported, but remained largely elusive.
“Understanding the adaptive responses in which the body produces antibodies that specifically bind to Sars-CoV-2 among Covid-19 patients provides critical information for developing an effective treatment and preventive vaccine.”
Previous studies have found the opposite of this, that antibodies can last for months after someone falls ill with the disease, while others have noted that people hardly develop immunity.
There is also some debate as to whether the severity of the disease plays a role.
People who become seriously ill and are hospitalized tend to have a stronger immune reaction and are therefore more likely to be protected in the future.
While those who have mild or even undetectable symptoms may not develop immunity at all.
There is no guarantee that people’s bodies will protect themselves, and scientists will only be able to confirm this over time.
Earlier this week, Health Secretary Matt Hancock said “credible” reports are now emerging of people contracting the disease more than once, something that had been deemed unlikely during the peak of the outbreak.
He told Parliament’s Health and Welfare Committee that the first ‘credible’ cases of coronavirus reinfection were beginning to be seen.
“We have also just started to see the first credible cases of reinfection and, through genomic analysis, you can see that it is a different disease than the one that the person contracted the first time.
“But in all the cases that I have seen, it has been a second asymptomatic infection that has been detected by asymptomatic tests.”
Hancock’s last point suggests that people don’t get noticeably sick the second time around and have no symptoms.
Commenting on the recent study, Danny Altmann, Professor of Immunology at Imperial College London and spokesperson for the British Society of Immunology, said: “ After initial posts on Sars-CoV-2 antibody assays and levels, Important articles are beginning to emerge that look at the specificity and durability of the answer in more detail.
Studies like this are a vital part of the ‘work in progress’ to understand who has immunity and for how long.
‘This article makes a number of points: the gold standard for assessing the antibody response to a virus is to measure the ability to neutralize the entry of the virus into cells, although this is not one of the routinely available tests.
“Most convalescent patients show this response, although, more importantly, 20% do not. Also, this antibody level drops in most people at the time of their follow-up appointment one month later.
Again, the evidence shows that the half-life of these antibodies in the blood is not particularly maintained.
“We don’t know how bad news is unless we know how much the white blood cells that make the antibody (B cells) are ready to defend against any repeated attack.”
The study was published in the scientific journal PLOS Pathogens.
