Lower antibody levels against variants highlight possible inadequacy of dosing schedule

7th June 2021

A study has demonstrated reduced efficacy against emerging COVID-19 variants after a single dose, highlighting the possible need to reduce the gap between vaccinations.

As mutations enable the emergence of COVID-19 variants, it is crucial to determine if the available vaccines are able to induce a satisfactory level of neutralising antibodies (NAbs) against any new variants. In a laboratory study, a team from the Francis Crick Institute and the National Institute for Health Research, set out to assess the level of NAbs produced in response to five COVID-19 variants, including the original viral strain as well as three others that have been deemed variants of concerns; B.1.167.2 (Delta or Indian variant), B.1.351 (South African variant) and the B.1.1.7 (UK variant). They also compared the level of NAbs produced in participants who had received either one or two doses of the BNT162b vaccine.

Findings
Among 159 participants who had received both doses of the vaccine, all samples produced a satisfactory NAbs response against each of the strains although six and nine individuals lacked detectable antibodies against the B.1.617.2 and B.1.351 respectively. However, despite the induction of NABs, levels were 5.8-fold less against the Delta variant compared with the original strain and 2.6-fold less against the B.1.1.7 although of a similar order of magnitude for the B.1.351. Interestingly, there was a significant correlation between NAbs and age, with titres significantly reduced among older individuals. A further finding of concern was that among a smaller cohort (14), who had been vaccinated between 8 and 16 weeks earlier, there was a significant reduction in NAbs titre against all of the variants.

Perhaps of most interest were the data from participants who had received only a single vaccine dose. After a median of 30 days post-vaccination, 79% of individuals had sufficient NAbs against the original strain, but this reduced to 50% for B.1.1.1, 32% for B.1.617.2 and to 25% for B.1.351.

In a discussion of these findings, the authors suggested that although NAbs levels are considerably reduced against the B.1.617.2 and B.1.351 after a single vaccination, this emphasised the importance of reducing the delay period (which has been set at 12 weeks) between doses.

Lead author of the study Emma Wall, said “This virus is likely to be around for some time to come, so we need to remain agile and vigilant. Our study is designed to be responsive to shifts in the pandemic so that we can quickly provide evidence on changing risk and protection”.

Citation
Wall EC et al. Neutralising antibody activity against SARS-CoV-2 VOCs B.1.617.2 and B.1.351 by BNT162b2 vaccination. Lancet 2021