Effectiveness of earlier COVID-19 and vaccination towards SARS-CoV-2 Omicron an infection

In a latest research revealed in The New England Journal of Medicine (NEJM), researchers studied the results of prior immunity on symptomatic an infection by the extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant.

Study: Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections. Image Credit: petovarga/Shutterstock
Research: Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections. Picture Credit score: petovarga/Shutterstock


The Omicron wave in Qatar started on December 19, 2021, and reached its peak by mid-January 2022. Whereas the Omicron BA.1 subvariant was predominant within the nation through the first few days, the BA.2 subvariant changed BA.1 and prevailed because the dominant variant. Though thought-about as subvariants, substantial genetic distance exists between the 2.

The safety towards these subvariants by prior SARS-CoV-2 an infection, vaccination, or each (hybrid immunity induced by an infection and vaccination) shouldn’t be but absolutely outlined.

Concerning the research

Within the current research, researchers assessed the protecting immunity conferred by the earlier an infection with variants aside from Omicron, coronavirus illness 2019 (COVID-19) vaccination, and hybrid immunity towards symptomatic BA.1 or BA.2 an infection. Effectiveness towards extreme and important sickness and loss of life was additionally estimated. Information on COVID-19 vaccination, testing, hospitalization, and loss of life had been obtained from nationwide federated databases, encompassing COVID-19-related info and related demographics.

Solely polymerase chain response (PCR)-tested people had been included. COVID-19 instances (PCR-positive people) and controls (PCR-negative) recognized between December 23, 2021, and February 21, 2022, had been matched in a 1:1 ratio based mostly on intercourse, nationality, and calendar week of PCR testing. Nonetheless, a 1:5 matching ratio was used to estimate effectiveness towards extreme, essential, or deadly instances to enhance statistical precision.

Reinfection was outlined as an infection occurring after no less than 90 days of beforehand documented an infection. Double and triple vaccinated contributors who obtained messenger ribonucleic acid (mRNA) vaccines solely (BNT162b2 or mRNA-1273) had been included within the research. Those that obtained heterologous vaccine doses had been excluded.

They categorized the research inhabitants as 1) SARS-CoV-2-naïve and double-vaccinated, 2) double-vaccinated with earlier an infection, 3) infection-naïve and triple-vaccinated, 4) triple-vaccinated with prior an infection historical past, and 5) non-vaccinated, contaminated. Odds ratios and related 95% confidence intervals (CIs) had been computed utilizing conditional logistic regression.


Through the research interval, there have been 1.3 million double-vaccinated people and 341,438 boosted contributors. The median interval between the primary and second dose and second and booster dose was 21 and 251 days, respectively. The research inhabitants was predominantly male and younger. Of the 315 PCR-positive samples randomly chosen for whole-genome sequencing, 300 had been Omicron infections, and 15 had been Delta infections. Most Omicron instances (76.2%) had been BA.2 infections.

The researchers discovered that the effectiveness of prior illness in non-vaccinated contributors was 50.2% towards symptomatic an infection with BA.1 variant. The efficacy of two doses of BNT162b2 within the infection-naïve inhabitants was negligible. Triple vaccination in these with out prior an infection confirmed 59.6% efficacy. In double vaccinated topics with the earlier illness, efficacy was 51.7%, and in beforehand contaminated topics who obtained three BNT162b2 doses, a 74.4% efficacy was noticed.  Excessive efficacy (>90%) was evident throughout all 5 teams towards extreme, essential, and deadly COVID-19 resulting from Omicron BA.1 an infection.

The authors famous 46.1% effectiveness among the many previously-infected non-vaccinated contributors towards an infection with BA.2 variant. Like with BA.1, efficacy towards BA.2 an infection was negligible amongst double-vaccinated infection-naïve topics. Efficacy was 52.2% in boosted, SARS-CoV-2-naïve contributors.

Double vaccination with the BNT162b2 vaccine in beforehand contaminated people was 55.1% efficient towards BA.2 an infection. Effectiveness towards BA.2 an infection was the best (77.3%) amongst beforehand contaminated folks vaccinated with three BNT162b2 doses. Total, the severity of Omicron BA.1 infections was low, with extreme, essential, and deadly instances constituting 0.3% of the overall (BA.1) infections. Equally, simply 0.3% of BA.2 contaminated sufferers had been hospitalized or died. 


The research discovered that earlier an infection with the non-Omicron variant roughly lowered an infection danger by 50%, with no profound variations between BA.1 and BA.2 subvariants. Notably, effectiveness towards both subvariant was negligible for SARS-CoV-2-naïve double-vaccinated topics. This might plausibly be defined by the declining immunity in vaccinated people, on condition that contributors obtained their second dose eight months in the past (or longer).

A 3rd vaccine dose roughly lowered the danger of an infection by 60%. The excessive efficacy could be as a result of most people obtained the booster 45 days earlier than inclusion within the research. Apparently, the safety conferred by hybrid immunity in double-vaccinated topics was much like the immunity induced by an infection alone. Boosted people with a historical past of COVID-19 had been essentially the most protected. There have been no pronounced variations among the many recipients of BNT162b2 and mRNA-1273 vaccines.

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