It is easy to get swamped by all the research on coronavirus. New Zealand’s Science Media Centre is keeping track of much of it so you don’t have to. The Research Tracker is prepared by Dr Robert Hickson for the Science Media Centre New Zealand.

Non-vaccine-related papers

Immune responses after infection can last for 15 months or more

Natural SARS-CoV-2 infections can generate immune responses that persist for at least 15 months. As previous studies have shown, the dynamics of antibodies and T cells differ. IgG antibody levels peaked two to four weeks after an infection, gradually declined over the next five months, and then stabilised. Persistence of IgG antibodies was associated with more severe disease. In contrast, some T cells showed significant declines between 6 and 15 months post-infection.

Neutralising antibody activity against an early viral strain was detectable in the majority of samples out to 15 months. Detection of antibodies and T cells months after infection indicates the development of B and T memory cells.

In tests of sera from people infected early in the pandemic some more recent variants, such as Delta, were able to partially escape the neutralising activity. The paper has not yet been peer reviewed.

Very potent neutralising antibody found from a natural infection

Testing of antibodies from infected patients has identified a very potent antibody that has strong neutralising activity against all four current variants of concern. When given to a small number of hamsters it prevented infection. The paper was published in Cell Reports.

RNA interference therapies may be able to control infections

Creating short pieces of double-stranded RNA to interfere with SARS-C0V-2 replication shows promise. Experiments using the technique called RNA interference (RNAi) found that one short interfering RNA (siRNA) sequence (21 nucleotides long) decreased viral replication by two-fold. The siRNA also stopped infected cells being damaged by the virus.

The siRNA showed potential for being effective against a broad range of variants since it targets a conserved region of the viral genome. It was active against the wild-type and Alpha variants, as well as SARS-CoV-1. The paper was published in Viruses.

Technical side note - a review article in Signal Transduction and Targeted Therapydescribes the clinical opportunities and challenges for RNAi. As of last year only two siRNA treatments had received approval for clinical use, but more are expected.

Delta variant may be more efficient at infecting some cell types

The Delta variant may be more transmissible because it can more quickly enter some cell types, and enhances cell-cell fusion. Comparisons were made with the wild type virus. Delta was two-fold more efficient that the wild type in infecting a human lung cell line, and 1.5-fold more efficient in infecting a human colon cell line. There were no differences in infection efficiency for two other cell lines. The authors note the limitations of studying infection using cultured cell lines. The paper was published in Cell Reports.

Persistence of Covid symptoms for 6 months may be common

A review of 57 studies found that more than half the subjects had Covid-19 symptoms six months after infection. A diverse range of symptoms were reported, including ones affecting mobility, breathing, neurological, mental health, and fatigue. Limitations in long Covid studies include the lack of consistent definitions of symptoms and reporting practices. The paper was published in JAMA Network Open.

Transmission in Norwegian and US schools

A Norwegian study found that schools were not an important venue for transmission. Primary schools (student ages 6 to 12) and lower secondary schools (13 to 15 year olds) were studied (with 2,600 schools included). These schools remained open during most of the pandemic, with infection prevention controls in place.  

Staff-to-staff transmission was slightly more common than student-to-student or student-to-staff transmission. Over half (55%) of index cases in schools did not infect others at the school, and 16% only infected one other person. Student-to-teacher transmission was higher in primary schools than in secondary schools. The paper is not yet peer reviewed.

A US study of K-12 schools (for 5 to 18 year olds) found that in-person learning increased infection rates. After controlling for a variety of factors the average growth rate of cases in open schools was 5% higher than in schools that had on-line learning. Case growth rate was higher in schools where mask wearing was not mandatory.

Not all confounding factors could be excluded from the study, and there was probably under-reporting of cases. The authors stress that they do not advocate keeping schools closed. They argue for good public health measures to reduce the risks of transmission within schools. The paper was published in the Proceedings of the National Academy of Sciences.

Norway and the US had quite different approaches to and levels of control of the pandemic, so the different findings aren’t contradictory.

‍

Subscribe to SMC-NZ's Coronavirus Research Tracker.