As a result of the Stanford University study, it may be possible to understand why receiving a second dose of mRNA vaccines, such as the Pfizer or Moderna shots, is so important in developing a strong immune system response against SARS-CoV2.
For example, according to study co-author Bali Pulendran, the current pandemic represents “the first time RNA vaccines have ever been given to humans, and we have no clue as to how [the vaccine] does what it does, which is provide 95 percent protection against COVID-19.” Dr. Pulendran is a professor of pathology at Stanford University, as well as of microbiology and immunology.
How mRNA-based vaccines can provide recipients with such extraordinarily high levels of protection against the new coronavirus has remained a mystery for decades. In comparison, a seasonal influenza vaccine is considered to be quite effective if it achieves even a 60 percent protection rate against the virus.
As part of their investigation, the Stanford team collected and analysed blood samples from 56 healthy volunteers at various points before and after they received their first and second doses of the Pfizer vaccine, respectively.
As a result of the study, it was discovered that the first shot increased SARS-CoV-2-specific antibody levels, but not by nearly the same amount as the second.
As reported by the university, “The second shot has powerful beneficial effects that far exceed those of the first shot,” Pulendran explained in a news release. According to the researchers, the treatment resulted in a significant increase in antibody levels, an extraordinary T-cell response that was absent after the first shot alone, and a significantly enhanced innate immune response.
Other immune system players, in addition to the standard antibodies that are usually studied, were investigated by the researchers.
When they did this, they discovered some intriguing new information: As reported on July 12 in the journal Nature, a second shot appears to be capable of performing tasks that the first shot was unable to complete.
To their surprise, the Stanford team discovered that a second dose of the Pfizer vaccine resulted in a significant mobilisation of a small group of first-responder immune cells, which were previously thought to be inactive and dormant.
These cells are a small subset of the normally abundant cells known as monocytes, which produce high levels of genes that have virus-fighting abilities and are therefore highly sought after.
The researchers discovered that when the COVID-19 virus infects a person, these monocytes are only minimally activated, if at all.
However, the findings of the study showed that monocytes do respond strongly to the vaccine — but only after the second dose, which was the most significant finding.
In the study conducted by Pulendran’s group, monocytes accounted for only 0.01 percent of all circulating blood cells before vaccination, but their numbers increased 100-fold after the second dose of Pfizer vaccine, when they accounted for a whopping 1 percent of all blood cells, according to the researchers.
According to Pulendran, the cells also became less inflammatory and more potently antiviral, and they appear to be capable of providing broad protection against a variety of viral infections in the laboratory.
“It is surprising to see such an extraordinary increase in the frequency of these cells just one day after receiving a booster immunisation,” he said. These cells may be capable of mounting a holding action against not only SARS-CoV-2 but also against other viruses, according to the researchers.
Already, studies have shown that strong immune responses against SARS-CoV-2 in people who have received two doses of mRNA vaccines may last for at least eight months, and possibly for years.
Dr. Amesh Adalja is an infectious disease expert and senior scholar at Johns Hopkins University in Baltimore, where he is affiliated with the Center for Health Security. Even though he was not involved in the new study, he stated that it “confirms that administration of the second dose of the mRNA vaccine regimens significantly increases the overall level of immunity conferred by the first dose.”
According to Adalja, “This is the rationale for a two-dose regimen and why people who are fully vaccinated are more protected than individuals who are partially vaccinated.” “Given that the Moderna vaccine and the Moderna vaccine both use similar technology, I expect the findings to be very similar.”