Longer intervals between primary Covid-19 vaccine doses generate nine times as many antibodies, according to a study.
The study, which is available only as a preprint and not peer-reviewed yet, found that higher antibody levels due to longer gaps between doses had more effect in younger participants.
Post-dose 1, those with previous infection had up to ten times higher antibody levels than naive individuals. After dose 2, those with previous infection had antibody levels more than twice as high as those who hadn't had previous infection.
While dosing intervals didn't affect antibody levels in those with previous infection, a longer gap between infection and vaccination was linked to higher antibody levels, said researchers at the UK Health Security Agency (UKHSA).
The findings were presented at this year's European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Portugal.
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Understanding the immune response to vaccination against Covid is integral to controlling the virus and reducing the number of deaths.
"This study shows that a longer time between vaccine dose 1 and dose 2 results in higher antibody responses in naive participants," said Dr Ashley Otter from the UKHSA.
"We've also shown that in those with previous infection, timing between exposure and vaccination plays a critical role in post-vaccination antibody responses. However, further research is needed to determine whether these higher antibody levels provide greater protection against Covid-19 disease and how this longer dosing interval may affect booster responses," Otter added.
For the study, the team measured antibody levels in blood samples taken from almost 6,000 healthcare workers from across the UK enrolled.
About 3,989 of the 5,871 participants had their first dose of the vaccine at least 21 days earlier, while 1,882 had their second dose at least 14 days earlier.
The participants were classified by infection history as either previously having had Covid or naive, with no history of infection. Almost all of those who hadn't had Covid seroconverted after vaccination, meaning they made antibodies against the virus.
Those who had their first dose of the vaccine eight months after an infection had antibody levels seven times higher than those who were vaccinated three months after infection. This suggests that eight months after primary infection may be an optimum time to receive the first vaccine in those with prior infection.
However, the analysis shows that regardless of timing between infection and vaccination, all individuals mount a very high antibody response after dose 2.
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In addition, the study showed that female participants and those from an ethnic minority were associated with significantly higher antibody titres, whilst immunosuppression was associated with significantly lower post-vaccination antibody responses.