Another paper looking at T cell development in 25 recovered coronavirus illness patients. (Medrxiv Paper) The authors were trying to identify how often memory T cells developed following infection and how variable the cells were–did they recognize different regions of the virus. This particular class of T cell is also a killer T cell–it can kill cells infected by the virus. The researchers looked at over 30 patients and did an extensive screening of their memory T-cells. They found multiple regions (called epitopes) in the virus that were recognized, most by a number of the patients. Few of these regions were in the spike protein, where the area used to gain entry into a cell is located (called the receptor binding domain). Most were in either the nucleocapsid protein or other regions. This has implications for vaccine composition. It may also be good because the regions “remembered” may be less likely to mutate to be unrecognizable. Other half the patients had T cell memories that reacted to the original SARS coronavirus, but only a few had a T cell memory that responded to the seasonal coronaviruses. Overall, the paper is positive for the likelihood of a robust and lasting adaptive immune response to possible reinfection by coronavirus.
More research on cross-reactive immune responses among coronaviruses. (Medrxiv Paper) Contrary to the study above, this paper found extensive cross-reactivity among antibodies. These researchers did a broad search for regions, or epitopes, in the virus proteins that raised antibody reactions, looking at all the human coronaviruses. They found a number of antibody targets in all patients. Non-infected subjects also had common antibodies against coronaviruses. They found one particular region on the S or spike protein that had particularly strong cross-reaction with one strain of the seasonal coronaviruses. They strongly suggest that a large number of individuals have strong pre-existing antibody responses that also impact the current strain.
This is an interesting topic regarding whether certain vaccinations provide some protective effect agains coronavirus. (Medrxiv Paper) There have been some other papers on this subject, but this one looked at a large group of individuals, over 137,000 treated at the Mayo Clinic, who were tested for coronavirus infection. After adjusting for a large number of potential confounding factors, they found that receiving an influenza, measles-mumps-rubella, pneumonia, or heatitis A/B vaccine in the last 1 to 5 years was associated with a significant reduction in CV infection rates. For African Americans, having a pneumonia vaccine seemed to reduce risk by almost half. There were very significant risk reductions for some sub-populations and vaccines. These results are consistent with some papers I reported on before, some from years ago, finding that certain vaccines, especially live attenuated ones, may provide a wide immune system boost. Trials are underway to specifically test some of these vaccines against CV.
More on viral loads. (Medrxiv Paper) This was a review of other research. One primary finding was that while virus RNA shedding can be found for an extended period, no study found live virus, capable of replication, beyond the 9th day of illness. So the common infection tests are worthless for telling you when you are no longer infectious. In general, the studies found lower viral loads and shorter periods of shedding for asymptomatic persons.