Highlighting strength of hybrid immunity to all variants, necessity of two doses for immunonaives, and perhaps waning of convalescent immunity after many months, two new studies.
A brief study (Emory) of convalescent (31-91 days post infection) and vaccine mediated (mRNA-1273 at 35-51 days, BNT162b2 at 7-27 days, each post second dose) sera neutralisation in live virus assays. Relative to earlier type (WA1/2020) kappa/B.1.617.1 was around 7x less susceptible, whilst delta/B.1.617.2 was around 3x less susceptible, to neutralisation by serum both from convalescents and vaccinees. Despite this finding, a majority of the convalescent sera (79% against kappa and 96% against delta) and vaccine mediated sera had detectable neutralising activity against both variants three months post-infection/second dose. Note the apparent greater degree of immune evasion exhibited by kappa over delta.
DOI: 10.1056/NEJMc2107799.
Second - an extension of an
earlier study from France (Institut Pasteur). Here examining neutralisation of sera from convalescents, BNT162b2 and AZD1222 partial/full vaccinees and single dose convalescents (hybrid immunity).
In sera from convalescents at 6 months post-infection (Orléans cohort*) a 4-6x reduction in neutralisation titres (antibodies to spike) against delta/B.1.617.2 was observed (versus alpha and D614G); likewise for another group where sera was collected at 12 months (Strasbourg cohort*). Single dose recipient convalescents (mixture of mRNA-1273, BNT162b2, AZD1222; separate Strasbourg cohort) exhibited strong immunoresponses, which at 12 months post-infection (7-81 days post dose) exhibited a smaller reduction in neutralisation titres against all variants tested, particularly delta/B.1.617.2 and beta/B.1.351.
Classifying neutralisers and non-neutralisers, convalescents varied widely with only around half neutralising beta or delta after one year. All single dose convalescents neutralised all variants at one year. For recipients of Pfizer, with low levels of neutralisation seen after one dose, reduction in neutralising titres after two doses was around 3x for delta and 16x for beta (compared to alpha/B.1.1.7). For AstraZeneca recipients this was 5x and 9x for delta and beta, respectively. Single vaccines doses were poor at neutralising variants.
Might hint BNT162b2 recipients would benefit from a later third dose.
* significantly longer post-infection than for the first study (3 months versus 6, 12 months).
DOI: 10.1038/s41586-021-03777-9.