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Why the 2nd Dose of Pfizer Vaccine Is So Crucial

By Ernie Mundell and Robert Preidt
Health Day Journalists

WEDNESDAY, July 21, 2021 (HealthDay News) – It takes two doses of the Pfizer-BioNTech COVID-19 vaccine to “wake up” the cells that play a very important role in the body’s immune response, with the second dose increasing their number 100 times, according to new research.

The Stanford University study may help explain why getting the second dose of mRNA vaccines, such as the Pfizer or Moderna vaccines, is so crucial in building a strong immune system response against SARS-CoV. -2.

As study co-author Bali Pulendran explained, the current pandemic marks “the first time that RNA vaccines have been given to humans, and we have no idea how they do this. what they do: offer 95% protection against COVID-19 ”. Pulendran is Professor of Pathology and Microbiology and Immunology at Stanford.

It has never been clear how mRNA-based vaccines provide recipients with such extraordinarily high levels of protection against the novel coronavirus. In comparison, a vaccine against the seasonal flu is considered quite effective if it achieves even 60% protection.

In their investigation, the Stanford team analyzed blood samples from 56 healthy volunteers at several times before and after receiving their first and second injections of the Pfizer vaccine.

The results showed that the first stroke increased the levels of SARS-CoV-2 specific antibodies, but not as much as the second stroke.

“The second shot has powerful beneficial effects that far exceed those of the first shot,” Pulendran said in a college press release. “It stimulated a multiple increase in antibody levels, a formidable T cell response that was absent after the first stroke alone, and a remarkably improved innate immune response.”

The researchers also looked at players in the immune system in addition to the standard antibodies that are typically studied.

When they did that, intriguing new details emerged: The second shot appears to do things the first shot can’t, according to the study published July 12 in the journal. Nature.

The Stanford team was surprised to find that a second dose of Pfizer vaccine triggered significant mobilization of a small group of first responder immune cells that are normally rare and dormant.

These cells are a small subset of normally abundant cells called monocytes, which produce high levels of genes with virus-fighting power.

When the COVID-19 virus infects a person, these monocytes are barely activated, if at all, the researchers found.

However, the study showed that the monocytes do react strongly to the vaccine – but mainly only after the second dose.

According to Pulendran’s group, monocytes made up only 0.01% of all circulating blood cells before vaccination, but their number increased 100-fold after the second dose of Pfizer vaccine, when they accounted for 1% of all blood cells.

In addition, the cells have become less inflammatory and more strongly antiviral, and appear to be able to provide broad protection against a range of viral infections, according to Pulendran.

“The extraordinary increase in the frequency of these cells, just one day after the booster vaccination, is surprising,” he said. “It is possible that these cells may be able to mount a maintenance action not only against SARS-CoV-2, but also against other viruses.”

Already, studies show that strong immune responses to SARS-CoV-2 can last at least eight months, or even years, in people who have received two doses of mRNA vaccines.

Dr Amesh Adalja is an infectious disease expert and senior researcher at the Center for Health Security at Johns Hopkins University in Baltimore. He was not involved in the new study, but said again that it “demonstrates that the second dose of mRNA vaccine regimens significantly increases the overall immunity provided by the first dose.

“This is the rationale for a two-dose regimen, and why fully vaccinated people are more protected than partially vaccinated people,” Adalja said. “I suspect the results would be very similar with the Moderna vaccine because they use similar technology.”

More information

The US Centers for Disease Control and Prevention has more on COVID-19 mRNA vaccines.

SOURCES: Amesh Adalja, MD, senior researcher, Center for Health Security, Johns Hopkins University, Baltimore; Stanford University School of Medicine, press release, July 17, 2021

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