It has almost been a given that the 26 million people around the world who have recovered from COVID-19 – out of a total of 35 million who have been infected, including over a million deaths – don’t have to worry about being infected again.
But is this true?
In the event of recurring exposure to the new Corona virus those who have recovered from the virus might be protected from being infected again, but it could be that they still carry the virus and can infect others.
Researchers at Tel Aviv University (TAU) who studied blood samples from 60 patients at the Hasharon Campus of the Rabin Medical Center in Petah Tikva examined immune memory in recovered individuals. They found that already after three months of recovery, the level of antibodies in the blood dropped below the threshold of detection, so that so that serological tests do not necessarily accurately reflect the spread of the disease in the population.
Antibodies in the blood decrease within just a few months
The team – Dr. Yariv Wine of TAU’s School of Biomedicine and Cancer Research, and led by post-doctoral fellow Anna Vaisman-Mentesh, together with Dr. Dror Dicker, director of an internal medicine department at the hospital – found that memory B cells specific to the virus remain stable over time, but concurrently the antibodies in the blood decrease within just a few months. This finding prompted the researchers to raise the possibility that in the event of re-infection with the virus, symptomatic illness will be insignificant.
They submitted their findings to MedRxRiv, an online site for complete but unpublished manuscripts founded by the non-profit Cold Spring Harbor Laboratory, Yale University, and BMJ, a global healthcare knowledge provider. The article was entitled “SARS-CoV-2 specific memory B cells frequency in recovered patient remains stable while antibodies decay over time.”
No data on immune memory over time among those recovered from the virus
Since the SARS-CoV-2 is a new virus, there is as yet no data on immune memory over time among those recovered from the virus. In the current research, the Israeli team checked the level of antibodies and the B cell count in their group of subjects. As has been shown in other studies, the antibodies acting on the viral protein responsible for attaching itself to target cells in the host body, develop very quickly, but they break down after recovery from the disease. In contrast, B cells that remember the viral proteins and can efficiently reactivate upon reinfection do not decline in recovered subjects over a period of six months.
“Corona is a serious illness and includes long-lasting side effects,” stressed Wine. “For that reason, rehabilitation centers have been established for those recovering from Corona, such as the one at Hasharon Hospital, and it also enables us to continue examining blood samples even many months after recovery.”
A stable level of memory B cells specific to the viral protein
From among the group of recovered patients who volunteered to be part of the research, they collected blood samples at predetermined time intervals – three months after onset of disease, and again three months later. From the data they collected, the team said that over at least a six- month period, the subjects maintained a stable level of memory B cells specific to the viral protein.
“The significance of this is that if these subjects become re-infected, their immune system can quickly respond – B cells will create a secondary reaction which may prevent illness. On the other hand, due to the decay of the antibodies, those who have recovered can still be carriers of the virus, and perhaps also be able to infect others,” continued Wine.
Serological surveys may be providing an inaccurate picture
Since the antibodies in the blood of those recovered from Corona decay with time, and in some cases even fall below detection threshold just three months after recovery, the team fear that serological surveys may be providing an inaccurate picture to decision-makers regarding spread of infection.
“Health organizations and the media talk a lot about serological surveys that check the level of antibodies in the blood, as a way of inferring the spread of disease in the population,” he added. “These surveys are very important, but in the light of the data on the decay of antibodies among recovered subjects, we might get a negative result when testing those who were infected in the past. If the antibodies are not maintained over time, and those who have recovered can still carry the virus and infect others, it is challenging to extrapolate from these surveys the breadth of infection spread in the population.”
Dicker concluded: “We are in a process of ongoing learning about Corona virus clinical illness when some recovered subjects still carry the virus. These findings add to our understanding of chronic illness from Corona and may shed light on future capabilities of the immune system of these recovered subjects.”