Immunocompromised patients tend to develop chronic coronavirus infections, leading to highly mutated variants that bear multiple antibody-resistant mutations, according to a new study carried out by a research team at Tel Aviv University, Israel.
The study involved an examination of chronic COVID-19 patients at the Tel Aviv Sourasky Medical Center (“Ichilov Hospital”) and was published this week in Nature Medicine.
The researchers found that a weakened antibody response, particular in the lower airways of these chronic patients, may prevent full recovery from the virus and drive the virus to mutate many times during a lengthy infection. They explained that the virus’ ability to survive and reproduce in the immunosuppressed patient’s body without restriction leads to the evolution of many variants.
The variants found among those chronically ill with COVID-19 bear many of the same mutations in their evolution as those present in variants-of-concern for severe illness, particularly those mutations associated with evading disease-killing antibodies. The new findings indicate that while rapidly-spreading variants are rare among the many strains borne from immunosuppressed patients, the likelihood increases and they do arise when global infection rates boom.
Since the outbreak of COVID-19, the rate at which the virus evolves has been somewhat puzzling, explained lead researcher, Professor Adi Stern. During the first year of the pandemic, a relatively slow but constant rate of mutations were observed. However, since the end of 2020, the world has witnessed the emergence of variants that are characterized by a large number of mutations, far exceeding the rate observed during the first year.
Various scientific hypotheses about the link between chronic COVID-19 patients and the rate of the accumulation of mutations have surfaced, but nothing definitive has been proven yet. In this new study, Prof. Stern and her team shed light on some pieces of this complex puzzle and try to answer the question of how variants are formed.
The coronavirus is characterized by the fact that in every population, there are people who become chronically infected. In the case of these patients, the virus remains in their body for a lengthy period of time, and they are at high risk for recurrent infection. In all of the cases observed so far, these were immunocompromised patients – part of their immune system is damaged and unable to function.
In biological evolutionary terms, these patients constitute an ‘incubator’ for viruses and mutations – the virus persists in their body for a long time and succeeds in adapting to the immune system, by accumulating various mutations.
Unfortunately, the study cannot shed any light on long Covid, she told The Brussels Times. Long Covid is a completely different story where symptoms persist despite no viral infection. Here we are looking at people who have lengthy viral infections, with active replicating virus.
“I believe that our research has succeeded in peeling back a missing layer of the big picture, and has opened the door for further research efforts to discover the origins of the various variants. This study highlights the importance of protecting immunocompromised individuals, who are at high risk for the virus, yet may also be an incubator for the formation of the next variant, posing a risk to all of us.”
Is there any estimate about the percentage of immunocompromised people in the population?
“They are generally rare, but it depends on where and what type and how many people undergo transplantations,” Professor Stern replied. “We saw that all the patients in our study suffered from one of the four following conditions: hematological cancer, AIDS, transplant patients, an auto-immune disease (the two latter were patients treated with immunosuppressive drugs).”
“Thanks to advances in medicine, the chances of immunocompromised people to survive blood cancer, transplants, etc. is much higher than in the past, and this means their percentage is low - but not negligible.”
How should they be protected in order to reduce the risk of new variants to develop?
“First of all, I think awareness of their personal risk (they are at increased risk for severe disease), as well as the risk to society from the development of variants - should be communicated clearly to physicians, patients, and policy makers.
Second, they should be monitored more closely. For example, one of our findings was that in some patients, there is supposed recovery, that is followed by the virus rebounding. So, there should be careful consideration of when such a patient should be released from quarantine.
Finally, as a society, each and every one has a personal responsibility to protect them. If I enter any crowded area, and especially a medical centre, I should put a mask on, both to protect myself but more importantly, to protect someone like these patients who might be present there.”
The Brussels Times