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Pfizer-BioNTech, Moderna jabs show better immunity

Immune system cells, or helper T cells, persist even after six months in people who received either the Pfizer-BioNTech or Moderna vaccines and help protect against the delta variant of SARS-CoV-2, according to a study by researchers at Johns Hopkins Medicine, US.

The study published in the Clinical Infectious Diseases journal showed that helper T cells remained at levels only slightly reduced from what was observed at two weeks after vaccination, for over six months; also, the levels were significantly higher than what was seen in people who were not vaccinated.

According to the US Centers for Disease Control and Prevention, the delta variant, the predominant strain of SARS-CoV-2 across the world at present, causes more infections and spreads faster than earlier variants of the virus.

“Previous research suggested that humoral immune response, where the immune system circulates virus-neutralizing antibodies, can drop off at six months after vaccination, while our study indicates that cellular immunity, where the immune system directly attacks infected cells, remains strong,” said Joel Blankson, professor of medicine at the Johns Hopkins University School of Medicine, and a senior author of the study.

“The persistence of these vaccine-elicited T cells, along with the fact that they’re active against the delta variant, has important implications for guiding covid-19 vaccine development and determining the need for covid-19 boosters in the future,” he said.

Blankson and his colleagues obtained blood samples from 15 study participants (10 men and five women) across three timelines: prior to vaccination, between seven and 14 days after their second Pfizer-BioNTech or Moderna vaccine dose, and six months after vaccination. The median age of the participants was 41 and none had evidence of prior SARS-CoV-2 infection.

The CD4+ T lymphocytes, or helper T cells, assist another type of immune system cell, the B lymphocyte (B cell), to respond to surface proteins (antigens) on viruses such as SARS-CoV-2. Activated by the CD4+ T cells, immature B cells become either plasma cells that produce antibodies to mark infected cells for disposal from the body, or memory cells that “remember” the antigen’s biochemical structure for a faster response to future infections.

Therefore, a CD4+ T cell response can serve as a measure of how well the immune system responds to a vaccine and yields humoral immunity.

The researchers also looked at the ability of CD4+ T cells six months after vaccination to recognize spike proteins atop the SARS-CoV-2 delta variant. They discovered the number of T cells recognizing the delta variant spike protein was not significantly different from that of T cells attuned to the original virus strain’s protein.

“The robust expansion of T cells in response to stimulation with spike proteins is certainly indicated, supporting the need for more study to show booster shots do successfully increase the frequency of SARS-CoV-2-specific T cells circulating in the blood,” said Blankson. “The added bonus is finding that this response also is likely strong for the Delta variant.”

In its latest weekly epidemiological update, the World Health Organization (WHO) said that the delta variant of SARS-CoV-2 virus has shown predominance globally with declining prevalence of other variants among sequences submitted to publicly available datasets or detections reported to WHO, the UN health agency said.

The delta variant, which was first detected in India, is now present in more than 104 countries.

India is expected to soon roll out Pfizer and Moderna vaccines for its nationwide vaccination drive. “The number of the fully vaccinated individuals has surpassed the partially vaccinated eligible population for the first time in the country. India has in total administered more than 1.13 billion doses as per the 7 am provisional reports today (Wednesday) with the administration of 67,82,042 vaccine doses in the last 24 hours,” said Mansukh Mandaviya, Union minister for health and family welfare. “The country will have vaccinated every Indian by the end of the month-long Har Ghar Dastak campaign,” he said.

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