COVID-19 study quantifies antibody response to Pfizer, Moderna vaccines

The difference was mostly noted in relatively older subjects. Researchers took blood samples from 167 vaccinated UVA employees one week to 31 days after their second dose. Some 79 were inoculated with the Pfizer vaccine, 88 with the Moderna vaccine. The average age of participants was 42, 38% were 50 or older, and 72% of them were women.

As doctors and scientists try to understand this virus and how to respond to it, UVA’s study provides a small but significant piece to the puzzle. However, researchers cautioned against drawing conclusions about the vaccines’ effectiveness based purely on antibody data.

They said that both vaccines performed “exceptionally” after being given to millions of people around the world.

Israelis above 60 years old receive their third dose of the COVID-19 vaccine at a Clalit health care maintenance organization, on August 08, 2021 in Jerusalem. (credit: OLIVIER FITOUSSI/FLASH90)

Though both vaccines are similar, the chemical formulations differ slightly, with Moderna using more mRNA than Pfizer. This provided the catalyst for researchers to quantify and compare the antibody responses to the vaccines.

The results were that the antibodies in Moderna were 68.5 micrograms per milliliter (µg/mL), and 45.9 for Pfizer.

To study the effect of age on antibody response, researchers divided participants into those younger than 50 and those older than 50.

The results showed that Pfizer recipients age 50 and older produced fewer antibodies (31.1 µg/mL) than younger recipients (59.0 µg/mL) after the second dose. This discrepancy was not seen in participants who were vaccinated with Moderna — researchers speculate that the difference is because Moderna uses more than three times as much mRNA as Pfizer in their vaccine.

Researchers note that they did not specifically look at “neutralizing” antibodies – the type of antibodies that block the virus from entering cells. They also did not look at T cells and B cells, which play a significant role in the body’s immune system. There is still a lot of research and study necessary in order to understand COVID-19.

While scientists advance in COVID-19 research, UVA immunologist Jeffrey Wilson, MD, Ph.D. strongly endorsed both the Pfizer and Moderna vaccines. Both greatly reduce the risk of serious illness or death, says Wilson. Researchers and scientists continue to study the vaccines’ long-term effectiveness, and whether booster shots will be needed – especially among older people, who may not have as strong an immune response as younger people.

As cases rise, Wilson asks of those not yet vaccinated, “Please, get your shot”.