SARS-CoV-2 Immunity: A Moving Target

(Posted on Thursday, January 28, 2021)

The ability of newly discovered variants to reinfect those who have recovered from earlier Covid-19 infection or those immunized with Covid vaccines is a hot topic. The two strains receiving the most attention are the SARS-CoV-2 variants from the United Kingdom (B.1.1.7) and South Africa (B.1.351). There is mounting evidence that they may be resistant to neutralization by antibodies directed against earlier stains. Definitive proof of resistance can be accomplished by measuring the neutralizing activity of antibodies in the sera from patients infected in the early months of 2020 against both the original and the variant viruses.

Scientists from Chongqing Medical University, China did just that in this study. They tested the activity of antibodies in the sera of twenty patients at two time points, in February and October. These patients were infected with SARS-CoV-2 in January and early February.

First, they examined the sera’s ability to neutralize the Wuhan strain circulating in China at the time of the January and early February infections. Sera collected in February had high titers of neutralizing antibodies against the original virus. That was not the case for antibodies in the sera of the same patients harvested eight months later. The neutralizing titers of the October sera fell between two to tenfold when measured against the original strain. A fall in neutralizing titers over time has been reported previously in some, but not all studies.

The February sera were significantly less effective in neutralizing both B.1.1.7 and B.1.351 than against the original virus strain. The average titer level for the original strain was 825, whereas it was 343 for B.1.1.7 and 148 for B.1.351. Some samples’ neutralization titers fell as much as ten times against the new variants, and six of 20 of the sample’s titers fell below the neutralization threshold against B.1.351.

The decline in neutralizing activity for the October sera was even more dramatic. Eight of the 20 October sera failed to neutralize the B.1.1.7 variant at all. Only two of the 20 showed any measurable neutralizing activity against B.1.351. These results suggest early infection offers little or no lasting protection against either of the two variants. 

The results of the Chongqing study are congruent with a study of the ability of antibodies in the sera of patients in South Africa infected in the summer of 2020 to neutralize B.1.351. The titer of the South African sera decreased compared to the original strain by two to three times. Notably, the original infecting strain in China was unlikely to carry the D614G mutation in the spike protein, whereas those responsible for infections in South Africa in the summer of 2020 almost certainly did have D614G substitution. However, given the ubiquity of neutralization escape from these two variants, it’s unlikely that will make a significant difference in the outcome.

Collectively, these studies provide a clear warning. First, neutralizing activity in the sera of those infected with SARS-CoV-2 decreases over time, at least in some populations, potentially leaving them susceptible to new infections by the original virus. Secondly, SARS-CoV-2 has the potential to evade immune responses induced by either vaccination or natural infections. Immune evasion coupled with increased transmissibility, as is the case for both the B.1.1.7 and B.1.351 variants, poses daunting public health challenges. Not only must we increase public health mitigation measures, but we must also be prepared for a long battle against a moving target.

Read the article on Forbes.

Originally published on January 28, 2021.