Study explores protection against Omicron and Delta infections by COVID-19 vaccination and previous infection

The Omicron BA.1 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant (Nextclade 21K, Pango lineage B.1.1.529/BA.1) emerged in November 2021 and rapidly spread across nations, owing to its higher transmissibility and immune escape.

Despite the reduced disease severity precipitated by infection with the Omicron SARS-CoV-2 variant, it imposes a substantial public health burden due to a large number of cases and the necessity for greater access to healthcare facilities.

Study: Protection of COVID-19 vaccination and previous infection against Omicron BA.1 and Delta SARS-CoV-2 infections, the Netherlands, 22 November 2021- 19 January 2022. Image Credit: Dmitry Demidovich/Shutterstock

Additionally, in vitro studies reveal reduced neutralization of the Omicron variant with convalescent sera, while the efficacy of the primary coronavirus disease 2019 (COVID-19) vaccination also appears to be limited. Although booster vaccination doses may be protective against Omicron, the effect is short-lived and less potent compared to booster vaccinations against Delta. However, the level of protection against Omicron infection induced by the combination of vaccinations and previous infections remains unknown.

The study

A new study posted to the medRxiv* preprint server demonstrated that infection- and vaccine-induced protection induced by the primary COVID-19 vaccination was much reduced for the Omicron BA.1 infection compared to the Delta infection.

In this study, a test-negative design was used to estimate the effects of primary and booster COVID-19 vaccinations, with and without previous infections, in preventing Omicron BA.1 infection compared to Delta. The study was conducted in the Netherlands, where the Omicron variant was first detected at the end of November 2021. S-gene target failure (SGTF) was used as a proxy for Omicron BA.1 infection. Here, data were derived from 528,488 community-based SARS-CoV-2 tests from two diagnostic laboratories, where they used the TaqPath COVID-19 RT-PCR Kit. The targets tested were – S, ORF1ab, and N.

Findings

During the study period ( from 22 November 2021 to 19 January 2022), 528,488 tests using the SGTF-PCR were included in the analysis, of which 84.8% were negative, 7.8% were positive for Delta, and 7.4% were positive for Omicron.  

The results suggested that previous infection, primary vaccination, or both, conferred adequate protection against Delta infection, while booster COVID-19 vaccination increased the protection against Delta, and this acquired immunity was further heightened among individuals who had a previous infection.

However, previous infection or primary COVID-19 vaccination provided markedly lower protection against Omicron BA.1 infection. Of note, the primary vaccination and previous infection combination were found to be more protective than each of these isolated factors. Meanwhile, the level of protection barely altered with the sequence of COVID-19 vaccination or infection.

The booster COVID-19 vaccination dose could enhance protection against the Omicron BA.1 infection in individuals with a previous infection. This effect too was significantly lower with the Omicron BA.1 variant than against Delta.

On the other hand, the effect of a primary COVID-19 vaccination against both Delta and Omicron BA.1 infection declined with time. For Omicron BA.1 infection, the relative reduction was 40-50% shortly after the primary vaccination or infection, which plummeted to 15-30% after 30 weeks. Whereas, for Delta infection, the relative reduction was 85-70% over time since the primary vaccination or infection. Furthermore, in individuals with both primary vaccination and prior infection, a waning of protection was observed over time since the last exposure (vaccination or infection). Meanwhile, protection post-booster vaccination was comparable to protection in individuals with primary vaccination and infection.

Interestingly, protection against Omicron BA.1 conferred by previous infection, was higher among children aged 0-11 years than in those aged 12-17 years of age. However, the efficacy of primary COVID-19 vaccination seemed to dwindle with increasing age for both variants. Individuals who contracted the infection before the initiation of the COVID-19 vaccination series exhibited increased protection against reinfection, with increasing age.

Conclusion

The results depicted that recently boosted individuals with a previous infection harbored the highest levels of protection against Omicron. However, primary COVID-19 vaccination and pre-Omicron SARS-CoV-2 infections offer low protection against Omicron BA.1 infection. Booster vaccination enhances protection against Omicron BA.1 infection, yet, to a lesser extent than against Delta.

It was inferred that the combined effect of the rapid Omicron spread, the severity of the disease, lower vaccine effectiveness against Omicron infection and booster vaccination coverage will determine the intensity of the current wave of the pandemic, its repercussions on hospitalizations, and the resultant healthcare burden posed by the Omicron variant.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Nidhi Saha

I am a medical content writer and editor. My interests lie in public health awareness and medical communication. I have worked as a clinical dentist and as a consultant research writer in an Indian medical publishing house. It is my constant endeavor is to update knowledge on newer treatment modalities relating to various medical fields. I have also aided in proofreading and publication of manuscripts in accredited medical journals. I like to sketch, read and listen to music in my leisure time.