In a recent study posted to the medRxiv* preprint server, researchers assessed the levels of neutralizing antibodies (NAbs) in coronavirus disease 2019 (COVID-19) patients.
Study: SARS-CoV-2 Omicron Variant Infection of Individuals with High Titer Neutralizing Antibodies Post-3rd mRNA Vaccine Dose. Image Credit: Huen Structure Bio/Shutterstock
This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources
Background
More than two years since the first outbreak of COVID-19 infections caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), effective containment of SARS-CoV-2 transmission is still a challenge that hinders return to normalcy. Although vaccination against SARS-CoV-2 has been extensively implemented across the continents, a significant proportion of the human population is yet to take a vaccine dose. Nonetheless, immunization has greatly helped to lower hospitalizations and avert severe disease.
The latest SARS-CoV-2 Omicron variant of concern (VOC) carries the highest number of mutations than previous VOCs, conferring the variant with high transmissibility and immune evasive characteristics. Some studies indicated that the Omicron variant could evade vaccine-induced immunity due to more pronounced NAb evasion than previous VOCs. However, the minimum NAb threshold to prevent COVID-19 remains undefined, particularly in Omicron infections.
The study
In the present study, researchers measured the NAb titers in Omicron-infected individuals boosted with the third dose of messenger ribonucleic acid (mRNA) vaccines. NAb titers were quantified using a rapid, semi-quantitative test measuring NAbs.
The study included a small cohort of participants from two time periods. While the first group of subjects had vaccine breakthrough infections before December 2021, the second subset comprised vaccine-boosted participants post-December 2021 reporting vaccine breakthrough infections driven by the Omicron variant. Females constituted about 57% and 64% of the pre-and post-December 2021 participants, respectively.
The study subjects received Pfizer’s BNT162b2 and Moderna’s mRNA-1273 vaccines. Booster vaccination was both homologous (three doses of BNT162b2 or mRNA-1273) and heterologous (two doses of mRNA1273 vaccine and one BNT162b2 booster or vice versa).
Results
There were 269 mRNA vaccinees in the study, and only 14 individuals reported vaccine breakthrough infections confirmed with reverse transcription-polymerase chain reaction (RT-PCR) tests before December 2021. Thirteen vaccine breakthrough cases (93%) occurred when their NAb titers dropped below 1:80 with neutralization ranging between 0 and 80% averaging at 16%, and the median neutralization was 17%. Only one vaccine breakthrough case had a NAb titer greater than 1:80.
After receiving an mRNA booster dose, the NAb titers were high with an average neutralization of 90%; NAb titer was more than 1:640 in nine individuals (64% of participants), ≥1:320 in two (14%), and ≥1:160 in three individuals (21%). These participants reported breakthrough infections with SARS-CoV-2 Omicron, a predominant variant in circulation.
Conclusions
The authors reported that the neutralizing antibody titers elicited after a third dose (booster) of current mRNA vaccines are inadequate to prevent symptomatic infections caused by the Omicron variant. The participants had self-reported symptoms like congestion in the upper respiratory tract, cough, myalgia, headache, fever, and lymphadenopathy.
Interestingly, even with the highest NAb titers of ≥1:640, vaccinated individuals remain highly susceptible to Omicron infection and could transmit the virus. Consistent with other reports, all participants had mild to moderate symptoms, and the booster dose prevented the severe outcome of the disease.
This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources
Article Revisions
- May 12 2023 - The preprint preliminary research paper that this article was based upon was accepted for publication in a peer-reviewed Scientific Journal. This article was edited accordingly to include a link to the final peer-reviewed paper, now shown in the sources section.
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