The Oxford-AstraZeneca and Pfizer-BioNTech vaccines deliver the genetic information that encodes for the SARS-CoV-2 spike protein to human cells, enabling them to produce this protein.
The production of the coronavirus spike protein by cells in the human body generates an immune response involving antibodies and T cells.
Neutralizing antibodies produced by B cells, which are a type of white blood cell, bind to the virus to disrupt its ability to infect human cells. Some studies have suggested that neutralizing antibody levels tend to predict the degree of protection against SARS-CoV-2 infection.
The levels of neutralizing antibodies
Moreover, vaccinated individuals tend to produce
In other words, the decline in the neutralizing antibody response may result in limited protection against SARS-CoV-2 infection.
Vaccination also results in the generation of memory immune cells that persist despite the decline in neutralizing antibodies. These memory cells form the second line of defense and prevent severe disease after the infection has occurred.
The presence of memory T cells, which are another type of white blood cell, can help launch a rapid T cell response after infection. T cells help eliminate infected cells to prevent the spread of the infection.
So, early activation of T cells due to vaccination plays a critical role in preventing severe COVID-19 and death.
Unlike the relatively drastic decline in neutralizing antibodies, the T cell response remains mostly intact.
Studies have suggested that COVID-19 boosters can help enhance immunity against the Delta variant and prevent breakthrough infections.
The recent study examined the effects of seven different COVID-19 vaccines as booster shots on the immune response at 28 days in individuals immunized with two doses of either the Pfizer-BioNTech or Oxford-AstraZeneca vaccine.
The researchers assessed the changes in antibody levels at 28 days to estimate the protective effects conferred by these booster vaccines against SARS-CoV-2 infection.
The clinical trial also assessed the T cell response and inflammatory adverse effects caused by these experimental booster shots.
The vaccines the researchers tested in the study were:
Lead study author Dr. Saul Faust, Ph.D., a professor at the University of Southampton in the United Kingdom, says: “The side effect data show all seven vaccines are safe to use as third doses, with acceptable levels of inflammatory side effects like injection site pain, muscle soreness, [and] fatigue.”
“[While] all boosted spike protein immunogenicity after two doses of AstraZeneca, only AstraZeneca, Pfizer-BioNTech, Moderna, Novavax, Janssen, and Curevac did so after two doses of Pfizer-BioNTech,” he adds.
Dr. James Shepherd, Ph.D. — a professor at Yale School of Medicine in New Haven, CT, who was not involved in the study — spoke to Medical News Today about the findings. He told us:
“The COV-Boost results from the U.K. are reassuring but not surprising. The broad ability of vaccines to boost each other in a heterologous prime-boost strategy, measured mainly by antibody increases as a surrogate for ‘real-world’ immunity, would be expected.”
“Most of the vaccines use the same antigen, the spike protein, as an immune stimulus and can therefore boost each other,” he explained. “This gives public health programs reassurance that booster campaigns can focus on delivering whatever shot is available into the arm rather than the more complicated distribution and delivery of ‘matching’ booster shots,” added Dr. Shepherd.
Source : https://www.medicalnewstoday.com/articles/covid-19-booster-vaccines-are-they-safe-and-effective766