In the case of single-dose recipients, our data show that NAbTs are significantly lower against B.1.617.2 and B.1.351 VOCs relative to B.1.1.7, implying that although a single dose might still afford considerably more protection than no vaccination, single-dose recipients are likely to be less protected against these SARS-CoV-2 variants. These data therefore suggest that the benefits of delaying the second dose, in terms of wider population coverage and increased individual NAbTs after the second dose,7 must now be weighed against decreased efficacy in the short-term, in the context of the spread of B.1.617.2. Worldwide, our data highlight the ongoing need to increase vaccine supply to allow all countries to extend second-dose protection as quickly as possible.
In the longer term, we note that both increased age and time since the second dose of BNT162b2 significantly correlate with decreased NAb activity against B.1.617.2 and B.1.351—both of which are also characteristic of the population in the UK at highest risk of severe COVID-19 (ie, older and vaccinated earlier), independent of other existing factors such as compromised immune status or comorbidity, or geographic-specific responses to vaccination.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)01290-3/fulltext