Seroprevalence in blood donors aged 17 years and older
The results presented here are based on testing samples with Roche nucleoprotein (N) and
Roche spike (S) antibody assays.
Nucleoprotein (Roche N) assays only detect post-infection antibodies, whereas spike (Roche S)
assays will detect both post-infection antibodies and vaccine-induced antibodies. Thus, changes
in seropositivity for the Roche N assay reflect the effect of natural infection. Increases in
seropositivity as measured by S antibody reflect both infection and vaccination. Antibody
responses to both targets reflect infection or vaccination occurring at least 2 to 3 weeks
previously given the time taken to generate a COVID-19 antibody response. Donors have been
asked to defer donations for at least 7 full days post vaccination, and for at least 28 days post
recovery if side-effects following vaccination or COVID-19 infection.
This report presents Roche N and Roche S seropositivity estimates on the same set of
samples, using a 12-week rolling prevalence for national, age group and regional estimates.
Seropositivity estimates are plotted using the mid-point of a 12-weekly rolling period that
reduces to 8 weeks in the most recent weeks to allow for a more representative current
estimate of seropositivity. Seroprevalence estimates reported are based on seropositivity which
are unadjusted for the sensitivity and specificity of the assays used.
N is not for Natural.