Immune responses to vaccines and vitamin D

 The rapid international effort to develop and deploy vaccines against the SARS-CoV-2 virus has been the pandemic's saving grace. But the story is far from over. Scientists must now thoroughly understand how our immune systems respond to various vaccines over time in order to continue to tweak and improve their efficacy as the virus evolves.

Researchers from Universiti Malaysia Sarawak (UNIMAS) examined blood samples from more than 300 vaccinees in the state of Sarawak in a paper published in Scientific Reports. They looked for the appearance of different antibodies up to 13 weeks after receiving the second dose of two different vaccines: Pfizer/BioNTech and Sinovac.

Each vaccine employs a unique strategy to elicit an immune response. The mRNA in the Pfizer/BioNTech vaccine codes for the spike protein found on the surface of the SARS-CoV-2 virus. When a person's cells begin to produce this protein, the immune system reacts by producing antibodies that recognize and bind to it, preventing the virus from attacking host cells. The Sinovac vaccine is made from whole inactivated viruses, which stimulates a broad immune response.

"We discovered that people who received the Pfizer/BioNTech vaccine produced significantly higher levels of antibodies that lasted significantly longer than those who received the Sinovac vaccine," UNIMAS virologist Cheng Siang Tan says.

According to Malaysian national statistics, people who received both doses of any vaccine had very low rates of intensive care admission (0.0066%) and death (0.01%). However, compared to Pfizer/BioNTech recipients, Sinovac vaccinees were more likely to require intensive care (5.5 times) or die (3 times).

Interestingly, according to the UNIMAS study, a small percentage of people (1.9%) who received the Sinovac vaccine failed to produce antibodies against the virus's spike protein three weeks after the second dose, while 2.9% had very low antibody levels at week 13. "This could explain why COVID-19-related deaths are higher among Sinovac recipients," Tan speculates.

The researchers also wanted to see if vitamin D deficiency affects a person's ability to develop a strong immune response following SARS-CoV-2 vaccination.

Despite Malaysia's proximity to the equator, they were surprised to discover that only 13.4% of the study population had adequate vitamin D levels. This could be due to people remaining indoors during lockdowns.

"We discovered that the magnitude and duration of antibodies were not dependent on serum vitamin D levels," Tan says.

Despite living near the equator, only 13.4% of the study population had adequate vitamin D levels. Surprisingly, the antibodies were not affected by vitamin D levels.

The researchers say their findings support a three-month interval between the second dose of the Sinovac vaccine and the subsequent booster, but recipients of the Pfizer/BioNTech vaccine, who have significantly higher antibody levels, may have to wait longer.

The researchers will then compare antibody responses in people who received booster doses of the same or a different vaccine.