An Assessment Of Post-vaccination Immune Response To SARS-Co
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Recent studies have revealed that vaccine-induced antibodies remained stable for about six months. To date, all of the vaccines that received EUA have been developed against the spike (S) protein of the original SARS-CoV-2 strain. Owing to the ability of this virus to frequently mutate, several SARS-CoV-2 variants have emerged. These variants have been classified as either variants of interest (VoI) and variants of concern (VoC) according to their virulence and rate of transmission.

In this study, six months follow-up visits were completed for 107 HCW, whose median age was estimated to be 35 years, as well as 82 elderly persons whose median age was 82.5 years. The authors of this study excluded participants who contracted COVID-19, as confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR), after receiving the first or second dose of the BNT162b2 vaccine.

The current study revealed that the anti-SARS-CoV-2 S1-immunoglobulin G (IgG) seropositivity rates decreased in the elderly group as compared to the HCW group six months post-vaccination. The researchers also found that the lowering of anti-RBD- and anti-full S-IgG levels in the serums of the elderly group was more pronounced than HCWs. The current study also reports a significant decrease in surrogate virus neutralization (sVNT) titers among the elderly at 56% as compared to 88.1.

In the current study, the researchers used the pseudovirus neutralization test (pNT) to determine the neutralization of the Delta variant post-vaccination. They revealed a substantial decline of serum neutralization of the Delta variant two months after the subjects received the first dose of vaccine and four weeks after the second dose. In 60.6% of the elderly vaccinated group, serum neutralization of the Delta variant was observed six months after vaccination.

This study also evaluated the neutralization of the Alpha variant in the same cohorts. To this end, 95.2% of HCWs and 69.0% of the elderly cohort could neutralize the Alpha variant six months following complete BNT162b2 vaccination. As expected, the mean neutralizing titers for both Alpha and Delta variants were significantly reduced in the elderly group as compared to younger HCWs.

The scientists observed that the emergence of viral variants containing mutations like E484K, which cause evasion of vaccine-induced immune responses or immune responses due to natural COVID-19 infection, would further reduce immunity among the old age group. In the elderly group, the researchers found a reduction in the binding capacity of serum antibodies to RBDs containing mutations such as K417N/T, L425R, T478K, E484K/Q, N501Y, and E484Q. These mutations are present in six known SARS-CoV-2 variants, thereby indicating that the vaccinated elderly group is still highly susceptible to COVID-19.