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.

KEYWORDS:

• COVID-19 vaccine
• Ct value
• case-case study
• real-world study
• booster immunization

Acknowledgements

We are very grateful for the data collection efforts by local CDC and infectious hospital staff of Zhengzhou, Yuzhou, and Anyang cities in Henan province.

Author contributors

ZDY, ZYW, XYW, XYL and YMS acquired funding and contributed to the study’s conception and design. ABW, RZ, ZHQ, FZW, HZ, ZJ and YY conceptualized the study and prepared the original study protocol, which was subsequently reviewed by LER. DW, LT, and CH developed the statistical methods. DW, CH and XYW wrote and tested the SAS code for the data analysis and drafted the manuscript. YY, HFW, YYZ, JJP, YFL, MXL, CSW and YTM collected data from local CDCs and abstracted the data. DW, LT, LER ZJA, ZDY and YMS interpreted the results and revised the manuscript and critically reviewed the manuscript. All authors approved the final submitted version.

Additional information

Funding

This work was supported by the Operation of Public Health Emergency Response Mechanism of Chinese Center for Disease Control and Prevention (131031001000200001).