A case–case study on the effect of primary and booster immunization with China-produced COVID-19 vaccines on prevention of pneumonia and viral load among vaccinated persons infected by Delta and Omicron variants

Abstract

Using a three-prefecture, two-variant COVID-19 outbreak in Henan province in January 2022, we evaluated the associations of primary and booster immunization with China-produced COVID-19 vaccines and COVID-19 pneumonia and SARS-CoV-2 viral load among persons infected by Delta or Omicron variant. We obtained demographic, clinical, vaccination, and multiple Ct values of infections ≥3 years of age. Vaccination status was either primary series ≥180 days prior to infection; primary series <180 days prior to infection, or booster dose recipient. We used logistic regression to determine odds ratios (OR) of Delta and Omicron COVID-19 pneumonia by vaccination status. We analysed minimum Ct values by vaccination status, age, and variant. Of 826 eligible cases, 405 were Delta and 421 were Omicron cases; 48.9% of Delta and 19.0% of Omicron cases had COVID-19 pneumonia. Compared with full primary vaccination ≥180 days before infection, the aOR of pneumonia was 0.48 among those completing primary vaccination <180 days and 0.18 among booster recipients among these Delta infections. Among Omicron infections, the corresponding aOR was 0.34 among those completing primary vaccination <180 days. There were too few (ten) Omicron cases among booster dose recipients to calculate a reliable OR. There were no differences in minimum Ct values by vaccination status among the 356 Delta cases or 70 Omicron cases. COVID-19 pneumonia was less common among Omicron cases than Delta cases. Full primary vaccination reduced pneumonia effectively for 6 months; boosting six months after primary vaccination resulted in further reduction. We recommend accelerating the pace of booster dose administration.

Effectiveness of Inactivated COVID-19 Vaccines against COVID-19 Caused by the SARS-CoV-2 Delta and Omicron Variants: A Retrospective Cohort Study

“…The risk of pneumonia, severe COVID-19, and fever with Omicron were significantly lower than with Delta, which is consistent with previous reports indicating that Omicron causes less severe COVID-19 than Delta [ 20 , 21 ]. Our study provided evidence for the protective effect of two-dose inactivated vaccines against Delta and booster vaccination against the Omicron variant.…”

“…Although two-dose VE against pneumonia with Delta was high, two-dose VE against pneumonia with Omicron is inadequate, which was inconsistent with results from another study [ 20 ]. The inconsistency may be primarily due to the waning immunity with time since 89.1% of two-dose-vaccinated Omicron cases were more than 6 months from second shot to infection.…”

An Overview of Signs and Symptoms to Determine Coronavirus and Omicron Patients in Primary Care and Hospitals

“…[13] In 2021 and 2022, most of the COVID-19 crises were brought on by Omicron and Delta variants. [14] Despite the little improvement after the booster dosage, vaccines give less protection against symptomatic Omicron infection than they do against the Delta form, according to observational studies in the general population. [14] Anxiety and despair have increased significantly since the COVID-19 pandemic, particularly after the Omicron wave.…”

Vaccinate with Confidence and Finish Strong

“…The Jilin Omicron BA.2 outbreak demonstrated that regardless of age group, primary series vaccination was associated with an impressive 9-fold reduction in severe COVID-19 and a 4-fold reduction in critical COVID-19, and that homologous boosting was associated with 44-fold and complete reductions in severe and critical COVID-19 (11). The relative impact of a booster dose of inactivated vaccine was further shown in a case-case study in an outbreak in Henan Province in early 2022 with 405 Delta infections and 421 Omicron infections.…”

“…The relative impact of a booster dose of inactivated vaccine was further shown in a case-case study in an outbreak in Henan Province in early 2022 with 405 Delta infections and 421 Omicron infections. Compared with primary vaccination 6-months before infection, a homologous booster dose reduced Delta COVID-19 pneumonia by an additional 82%, primary series alone reduced Omicron pneumonia by 66%, and there were too few boosted Omicron pneumonia cases (2 cases) to estimate relative VE ( 12 ).…”