An interval of eight to 10 weeks between doses of Pfizer and BioNTech developed COVID-19 vaccine boosts the effectiveness of the two-shot regimen compared with a shorter interval, a UK study found.
“Eight weeks is probably the sweet spot,” in terms of the trade-off between getting as many people fully vaccinated as quickly as possible and allowing the population to produce higher antibody levels, professor Susanna Dunachie, the study lead from the University of Oxford, said.
The study might help inform vaccination strategies against the Delta variant, which reduces the effectiveness of the first dose of the COVID-19 vaccine even though two doses are still protective.
“For the longer dosing interval, neutralizing antibody levels against the Delta variant were poorly induced after a single dose, and not maintained during the interval before the second dose. Following two vaccine doses, neutralizing antibody levels were twice as high after the longer dosing interval compared with the shorter dosing interval,” the authors of the study, which is being led by the University of Oxford, said.
The study looked at the immune response to the Pfizer vaccine ranging from a three-week dosing interval to 10 weeks. While the shot generated a strong reaction across the timespan, the long gap showed some advantages.
Neutralizing antibodies are thought to play an important role in immunity against the coronavirus, but not the whole picture, with T cells, also playing a part. The study found overall T cell levels were 1.6 times lower with a long gap compared with the short dosing schedule of 3-4 weeks, but that a higher proportion were “helper” T cells with the long gap, which supports long-term immune memory.
The authors emphasized that either dosing schedule produced a strong antibody and T cell response in the study of 503 healthcare workers.
The findings, issued as a pre-print, support the view that while a second dose is needed to provide full protection against Delta, delaying that dose might provide more durable immunity, even if that’s at the cost of protection in the short term.
Global studies show that both the short and long dosing schedules lead to strong real-world protection against COVID-19, emphasizing the importance of having a second dose of the vaccine, the researchers said.
Last December, Britain extended the interval between vaccine doses to 12 weeks, although Pfizer warned there was no evidence to support a move away from a three-week gap. Britain now recommends an 8-week gap between vaccine doses to give more people high protection against Delta more quickly, while still maximizing immune responses in the longer term.