There are two kinds that make anti-spike antibodies: long-lived plasma cells and memory B-cells. It is this help in antibody production that makes these vaccines so effective.īut not all B-cells are the same. The T-cells do this through direct contact with the B-cells and by sending chemical signals that tell the B-cells to produce antibodies. The mRNA vaccines are uniquely capable of inducing a special kind of immune cell – called a T-follicular helper cell – to help B-cells produce antibodies. Kateryna Kon/Science Photo Library via Getty Images When this memory B-cell is activated with an infection or the second dose of the vaccine, this causes some of the B-cells to change into plasma B-cells that secrete protective antibodies that fight the virus. T-cells provide information about the viral spike protein to B-cells, which are transformed to memory B-cells that store information about the virus. These immune cells then show the spike glycoprotein to B-cells, which then make anti-spike antibodies.ĭendritic cells recognize viruses and present information about the spike protein to T-cells. The dendritic cells use the instructions written in the mRNA to synthesize the hallmark spike glycoprotein, which characterizes the SARS-CoV-2 virus that causes COVID-19. Upon injection of the vaccine, the mRNA enters into immune cells called dendritic cells. Pfizer and Moderna vaccines use messenger RNA that encodes the spike glycoprotein. The biology through which the mRNA vaccines induce their protection from COVID-19 is fundamentally different from that with other vaccines. What the immune system does between the first and second dose But the good news is that even while supplies remain limited, the science suggests that there’s nothing bad about getting a second dose as late as 42 days after the first. Since protection was approximately 95% for everyone who was vaccinated within this time “window,” there is little reason not to allow some flexibility in the timing of the second dose 2.Īs more vaccine becomes available, the timing of the second dose should be close to four weeks for the Pfizer and Moderna vaccines. In the clinical trial, the second dose of the Pfizer vaccine was administered as early as day 19 and as late as day 42 to 93% of the subjects. Why the CDC decided receiving the second dose within 42 days is OK In the case of the Pfizer and Moderna COVID-19 vaccines, the second dose increases the protection afforded by the vaccine from 60% to approximately 95%.
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