To the Editor:

The omicron (B.1.1.529) variant of extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is answerable for coronavirus illness 2019 (Covid-19), has unfold quickly around the globe and has already turn out to be the predominant variant circulating in lots of nations. As of February 2022, omicron variants have been divided into 4 distinct sublineages: BA.1, BA.1.1, BA.2, and BA.3.¹ Most circulating omicron variants belong to sublineage BA.1; nevertheless, in Denmark, India, and the Philippines, the sublineage BA.2 is now changing into dominant.²

As in contrast with the Wuhan/Hu-1/2019 reference pressure, the sublineage BA.2 of the omicron variant has 16 amino acid substitutions within the receptor-binding area of the spike (S) protein of SARS-CoV-2,² which is the first goal for monoclonal antibody–based mostly remedy. The BA.2 and BA.1 variants share 12 of those 16 substitutions; nevertheless, BA.2 has 4 substitutions within the receptor-binding area (i.e., S371F, T376A, D405N, and R408S) that differ from these in BA.1. These findings counsel that there could also be variations within the effectiveness of monoclonal antibodies in opposition to these totally different omicron sublineages.

Accordingly, we examined the neutralizing potential of therapeutic monoclonal antibodies which have been accepted by the Meals and Drug Administration, individually and together, in opposition to the omicron BA.2 subvariant hCoV-19/Japan/UT-NCD1288-2N/2022 (omicron/BA.2; NCD1288), which was remoted from a traveler who arrived in Japan from India. Entire-genome sequencing evaluation of the NCD1288 virus inventory confirmed that it had the 16 substitutions which might be attribute of the omicron variant within the receptor-binding area of the S protein, as in contrast with the Wuhan/Hu-1/2019 reference pressure (Desk S1 within the Supplementary Appendix, obtainable with the complete textual content of this letter at NEJM.org).

Desk 1. Desk 1. Efficacy of Monoclonal Antibodies and Antiviral Medication in opposition to the Omicron/BA.2 Subvariant in Vitro.

A live-virus focus discount neutralization take a look at (FRNT) confirmed that each LY-CoV016 (marketed as etesevimab) and LY-CoV555 (marketed as bamlanivimab), individually and together, misplaced neutralizing exercise in opposition to omicron/BA.2 (NCD1288) (Desk 1). These findings are just like our earlier findings with omicron/BA.1 (hCoV-19/Japan/NC928-2N/2021; NC928)³ and omicron/BA.1.1 (hCoV-19/Japan/NC929-1N/2021; NC929).⁴ BA.1.1, a subvariant of BA.1, has the R346K mutation within the S protein (Desk S2). Nonetheless, REGN10987 (marketed as imdevimab), which was beforehand proven to lose neutralizing exercise in opposition to omicron/BA.1 (NC928) and omicron/BA.1.1 (NC929),^3,4 had neutralizing exercise in opposition to omicron/BA.2 (NCD1288).

As well as, the mix of REGN10987 and REGN10933 (marketed as casirivimab) additionally inhibited omicron/BA.2 however didn’t inhibit omicron/BA.1 or omicron/BA.1.1. Nonetheless, the FRNT₅₀ (the titer of monoclonal antibodies required for a 50% discount within the variety of infectious foci) worth of this mix remedy was larger by an element of 43.0 to 143.6 for omicron/BA.2 than for an ancestral pressure — SARS-CoV-2/UT-NC002-1T/Human/2020/Tokyo (NC002) — and different variants of concern (i.e., the alpha [B.1.1.7]beta [B.1.351]gamma [P.1]and delta [B.1.617.2] variants).

REGN10933, COV2-2196 (marketed as tixagevimab), and COV2-2130 (marketed as cilgavimab) neutralized omicron/BA.2. The COV2-2196–COV2-2130 mixture inhibited omicron/BA.2 with a low FRNT₅₀ worth (14.48 ng per milliliter); nevertheless, the FRNT₅₀ values of this mix have been larger by an element of 1.4 to eight.1 for omicron/BA.2 than for the ancestral pressure and different variants of concern.

S309 (the precursor of sotrovimab), which has been proven to have decrease neutralizing exercise in opposition to omicron/BA.1 and omicron/BA.1.1 than in opposition to the ancestral pressure and different variants of concern,^3,4 had even much less neutralizing exercise in opposition to omicron/BA.2 in our research. The FRNT₅₀ worth of this monoclonal antibody was larger by an element of 12.2 to 49.7 for omicron/BA.2 than for the ancestral pressure and different variants of concern.

The susceptibilities of omicron/BA.2 (NCD1288) to remdesivir, molnupiravir, and nirmatrelvir have been just like these of the ancestral pressure and different variants of concern (i.e., 50% inhibitory focus values for these three brokers that differed by elements of two.5 to 4.5, 0.7 to 1.6, and 1.5 to three.3, respectively) (Desk 1).³ Scientific research are warranted to find out whether or not these antiviral therapies are certainly efficient in opposition to omicron/BA.2 infections. Our knowledge point out that some therapeutic monoclonal antibodies (REGN10987–REGN10933, COV2-2196–COV2-2130, and S309) have decrease neutralizing exercise in opposition to omicron/BA.2 than in opposition to earlier variant strains.

Emi Takashita, Ph.D.
Nationwide Institute of Infectious Ailments, Tokyo, Japan

Noriko Kinoshita, MD
Nationwide Heart for International Well being and Medication, Tokyo, Japan

Seiya Yamayoshi, D.V.M., Ph.D.
Yuko Sakai-Tagawa, Ph.D.
College of Tokyo, Tokyo, Japan

Seiichiro Fujisaki, Ph.D.
Nationwide Institute of Infectious Ailments, Tokyo, Japan

Mutsumi Ito, DVM
Kiyoko Iwatsuki-Horimoto, DVM, Ph.D.
College of Tokyo, Tokyo, Japan

Peter Halfmann, Ph.D.
College of Wisconsin–Madison, Madison, WI

Shinji Watanabe, DVM, Ph.D.
Nationwide Institute of Infectious Ailments, Tokyo, Japan

Kenji Maeda, M.D., Ph.D.
Nationwide Heart for International Well being and Medication, Tokyo, Japan

Masaki Imai, DVM, Ph.D.
College of Tokyo, Tokyo, Japan

Hiroaki Mitsuya, MD, Ph.D.
Norio Ohmagari, M.D., Ph.D.
Nationwide Heart for International Well being and Medication, Tokyo, Japan

Makoto Takeda, M.D., Ph.D.
Hideki Hasegawa, M.D., Ph.D.
Nationwide Institute of Infectious Ailments, Tokyo, Japan

Yoshihiro Kawaoka, DVM, Ph.D.
College of Tokyo, Tokyo, Japan
[email protected]

This letter was printed on March 9, 2022, at NEJM.org.