New evidence shows why the second vaccination from the coronavirus vaccine program matters together with the risks around only having one jab, and skipping the other, in relation to the severity of the COVID-19 disease.
Research shows how a second dose of a COVID-19 vaccine induces an important boost to part of the immune system that provides broad antiviral protection. In doing so, Stanford University School of Medicine researchers have set out why second shot should not be skipped.
According to lead researcher Dr. Bali Pulendran, the laboratory studies probed the immune response induced by one vaccine and by two vaccine shots in great detail. The research used the vaccine marketed by Pfizer Inc., and modelled this against numerous components of the immune response. This was drawn out from samples of blood taken from people who had been given the vaccine.
Using the blood samples, the researchers counted antibodies, measured levels of immune-signalling proteins, and characterized the expression of every single gene in the genome of 242,479 separate immune cells’ type and status. This wider scope was needed because antibodies alone do not fully reflect the immune system complexity and potential range of protection.
This was important as the coronavirus vaccine represented the first time that RNA vaccines had been given to humans. Both the Pfizer and Moderna vaccines are RNA vaccines, and they contain genetic recipes for manufacturing the spike protein that SARS-CoV-2, the virus that causes COVID-19, uses to latch on to cells it infects. These vaccines therefore teach our cells how to make a protein that triggers an immune response inside our bodies.
The most influential immune-system component examined were T cells. These are a type of search-and-destroy immune cells that probe the body’s tissues for cells bearing signs of viral infections. On finding them, they proceed to tear the infected cells up.
By assembling the data, the scientists found that the first shot increases SARS-CoV-2-specific antibody levels, but not nearly as much as the second shot does. The second shot also
has powerful beneficial effects that far exceed those of the first shot, such as stimulating a large increase in antibody levels. The second dose triggered a large mobilization of first-responder cells that are normally scarce and quiescent.
These cells are a group of monocytes that are part of the innate immune system (CD14+CD16+ inflammatory monocytes), which normally constitute only 0.01% of all circulating blood cells prior to vaccination. However, following the second Pfizer-vaccine shot, the numbers expand 100-fold to reach 1% of all blood cells.
In relation to other infections, these cells may be able to mount a holding action against not only SARS-CoV-2 but against other viruses.
The research is published in Nature, with the paper titled “Systems vaccinology of the BNT162b2 mRNA vaccine in humans.”