An interesting article published by Cromer and others in The Lancet, November 15 discusses this issue.
Several SARS-CoV-2 variants of concern have been identified which partly escape serum neutralisation elicited by the current vaccines.
Studies have also shown that vaccines demonstrate reduced protection against symptomatic infection with SARS-CoV-2 variants. This study explored whether in-vitro neutralisation titres remain predictive of vaccine protection from infection with SARS-CoV-2 variants.
This meta-analysis used data from 24 identified studies on in-vitro neutralisation and clinical protection to understand the loss of neutralisation to the existing SARS-CoV-2 variants of concern.
They integrated the results of this analysis into their existing statistical model relating in-vitro neutralisation to protection. They also analysed data on boosting of vaccine responses and used the model to predict the impact of booster vaccination on protection against SARS-CoV 2 variants.
The neutralising activity against the ancestral SARS-CoV-2 was highly predictive of neutralisation of variants of concern.
Decreases in neutralisation titre to the alpha, beta, gamma and delta variants were not significantly different between the different vaccines. Neutralisation remained strongly correlated with protection from symptomatic infection with SARS-CoV-2 variants of concern and the existing model remained predictive of vaccine efficacy against variants over time and this suggested protection against symptomatic infection might decrease below 50% within the first year after vaccination for some vaccines.
Boosting of previously infected individuals with existing vaccines is predicted to provide a higher degree of protection from infection with variants of concern than primary vaccination schedules alone.
The geometric mean of the decrease in neutralisation titres was found to be 1.6 fold for alpha, 8·8 fold for beta, 3·5 fold for gamma, and 3·9 fold for delta compared with the ancestral virus.
Despite the variability in study designs, this meta-analysis found that predicted serological neutralisation activity against each variant elicited by vaccines was significantly correlated with protection from symptomatic SARS-CoV-2 infection.
The combined effects of waning immunity and reduced recognition of the SARS-CoV-2 variants of concern suggested that vaccine boosters would be needed to maintain protection of more than 50% against symptomatic SARS-CoV-2 infection. This analysis suggested that maximising neutralising antibody responses to the ancestral virus, through booster vaccinations of previously infected individuals should be an effective strategy to broadly increase neutralisation titres against SARS-CoV-2 variants.
In conclusion, this analysis suggests that good protection against the current variants of concern could be achieved by vaccination with existing vaccines using ancestral spike targets and the boosting with these vaccines is probably an effective strategy to combat the waning of immunity and the current variants of concern.
In the future, vaccines targeting novel variants of concern would be required if highly escaped variants arrive, but existing vaccines provide an effective method for boosting immunity against the current variants of concern.
The London General Practice the leading London doctors’ clinic in Harley Street commends the government on its vaccination program and encourages all those eligible to have their initial vaccines and to have their booster doses.
Dr Paul Ettlinger
BM, DRCOG, MRCGP, FRIPH, DOccMed