Vaccine effectiveness against hospital admission in South African health care workers who received a homologous booster of Ad26.COV2 during an Omicron COVID19 wave: Preliminary Results of the Sisonke 2 Study

Abstract

Following the results of the ENSEMBLE 2 study, which demonstrated improved vaccine efficacy of a two-dose regimen of Ad26.COV.2 vaccine given 2 months apart, we expanded the Sisonke study which had provided single dose Ad26.COV.2 vaccine to almost 500 000 health care workers (HCW) in South Africa to include a booster dose of the Ad26.COV.2. Sisonke 2 enrolled 227 310 HCW from the 8 November to the 17 December 2021. Enrolment commenced before the onset of the Omicron driven fourth wave in South Africa affording us an opportunity to evaluate early VE in preventing hospital admissions of a homologous boost of the Ad26.COV.2 vaccine given 6-9 months after the initial vaccination in HCW. We estimated vaccine effectiveness (VE) of the Ad26.COV2.S vaccine booster in 69 092 HCW as compared to unvaccinated individuals enrolled in the same managed care organization using a test negative design. We compared VE against COVID19 admission for omicron during the period 15 November to 20 December 2021. After adjusting for confounders, we observed that VE for hospitalisation increased over time since booster dose, from 63% (95%CI 31-81%); to 84% (95% CI 67-92%) and then 85% (95% CI: 54-95%), 0-13 days, 14-27 days, and 1-2 months post-boost. We provide the first evidence of the effectiveness of a homologous Ad26.COV.2 vaccine boost given 6-9 months after the initial single vaccination series during a period of omicron variant circulation. This data is important given the increased reliance on the Ad26.COV.2 vaccine in Africa.

Vaccines elicit highly conserved cellular immunity to SARS-CoV-2 Omicron

“…Median Omicron spike-specific CD8 + T cell responses were 82-84% of the WA1/2020 spike-specific CD8 + T cell responses. These data provide immunological context for the observation that current vaccines still show robust protection against severe disease with the SARS-CoV-2 Omicron variant despite the substantially reduced neutralizing antibody responses 7,8 .…”

“…Recent studies have shown that Ad26.COV2.S and BNT162b2 provided 85% and 70% protection, respectively, against hospitalization due to the Omicron variant in South Africa 7,8 . Our data provide immunological context for the observation that current vaccines still provide robust protection against severe disease due to the SARS-CoV-2 Omicron variant despite substantially reduced neutralizing antibody responses.…”

Rapid emergence of SARS-CoV-2 Omicron variant is associated with an infection advantage over Delta in vaccinated persons

“…Our findings may also explain why Omicron has been associated with more reinfections 12 . While Omicron was more likely to cause infections in vaccinated persons than Delta, vaccination shows maintained effectiveness in reducing severe disease, even for Omicron 13 . Together with the rebound of vaccine effectiveness after administering a booster dose 14 , measures to expand the uptake of the primary vaccine series and additional booster doses remain an important strategy for controlling the COVID-19 pandemic.…”

COVID-19 Vaccine: Between Myth and Truth

“…A third dose of the mRNA-1273 vaccine showed a vaccine efficacy of 67.7% (compared with the ~40% efficacy of two doses) against Omicron infection [121]. Data from a South Africa study involving healthcare workers (n = 227,310) who received the single-dose Johnson & Johnson COVID-19 vaccine as a primary dose showed that the booster increased vaccine effectiveness against hospitalization to 85% [129]. From these early data, it can be deduced that, with a third dose, the antibodies generated are able to effectively neutralize the virus, bringing protection from infection and serious disease back to high levels.…”

“…In one study, it was observed that multiple plasma specimens from recipients of the Ad26.COV2.S vaccine obtained 1 or 5 months after vaccination lacked detectable neutralizing activity against the Omicron variant[128]. One study observed that vaccine effectiveness against the B.1.1.529 variant for hospitalization was 63%[129].…”