Currently, an interval of three weeks is recommended between the first and second vaccination. A British study is now suggesting that a greater distance could possibly be better for older adults. The data are from a period of limited vaccine availability in the UK at the end of 2020.
The antibody levels of people over the age of 80 who received the two first vaccinations with the vaccine from Biontech / Pfizer were examined. The result: If a longer interval than the recommended three weeks was observed, the antibody reaction after the second vaccination was more than three times as strong.
According to the authors, this is the first study to investigate how increasing the vaccination interval affects antibody levels. “This study continues to support growing body of evidence that the UK approach to delaying this second dose has really paid off, ”said Gayatri Amirthalingam, epidemiologist at Public Health England in London and co-author of the preprint.
3.5 times higher antibody levels
Amirthalingam and colleagues studied 175 vaccine recipients over 80 who received their second dose of Pfizer vaccine either three weeks or eleven to twelve weeks after the first dose. The team measured antibody levels against the SARS-CoV-2 spike protein and looked at how immune cells called T cells, which can help maintain antibody levels over time, responded to the vaccination.
Maximum antibody levels were 3.5 times higher in those who waited twelve weeks to be boosted than those who waited only three weeks. The maximal T cell response was lower in those with the extended interval. However, this did not result in antibody levels falling any faster in the nine weeks following the booster.
The results are reassuring but specific to the Biontech / Pfizer vaccine, which is not available in many low- to middle-income countries, said Alejandro Cravioto, chair of the World Health Organization’s strategic advisory group of immunization experts. Countries would need to check whether the variants circulating in their respective regions could increase the risk of infection after just one dose of vaccine, he says.
For the UK, extending the interval between doses was the right choice, according to the researchers, says Stephen Griffin, a virologist at the University of Leeds, UK. However: “In theory, people are vulnerable between their first and second impact,” he says. “What has worked in the UK is keeping the restrictions in place at the same time as vaccination.”