Immunogenicity of the BA.1 and BA.4/5 Bivalent Boosts: A Brief Report of Preliminary Results from the COVAIL Randomized Clinical Trial (preprint)

The emergence of Omicron subvariants and waning immunity to initial vaccine regimens led to the authorization of updated SARS-CoV-2 bivalent vaccines containing wildtype with either Omicron BA.1 or BA.4/5. Here, we compare early serologic responses from a randomized clinical trial of a second boost with either the Pfizer/BioNTech BNT162b2 (30 mcg dose) Wildtype/Omicron BA.1 or Wildtype/Omicron BA.4/5 vaccines against homologous and heterologous strains including contemporary Omicron subvariants BQ.1.1 and XBB.1.

SARS-CoV-2 Variant Vaccine Boosters Trial: Preliminary Analyses (preprint)

Background: Protection from SARS-CoV-2 vaccines wanes over time and is compounded by emerging variants including Omicron subvariants. This study evaluated safety and immunogenicity of SARS-CoV-2 variant vaccines. Methods: This phase 2 open-label, randomized trial enrolled healthy adults previously vaccinated with a SARS-CoV-2 primary series and a single boost. Eligible participants were randomized to one of six Moderna COVID19 mRNA vaccine arms (50 mcg dose): Prototype (mRNA-1273), Omicron BA.1+Beta (1 or 2 doses), Omicron BA.1+Delta, Omicron BA.1 monovalent, and Omicron BA.1+Prototype. Neutralization antibody titers (ID50) were assessed for D614G, Delta, Beta and Omicron BA.1 variants and Omicron BA.2.12.1 and BA.4/BA.5 subvariants 15 days after vaccination. Results: From March 30 to May 6, 2022, 597 participants were randomized and vaccinated. Median age was 53 years, and 20% had a prior SARS-CoV-2 infection. All vaccines were safe and well-tolerated. Day 15 geometric mean titers (GMT) against D614G were similar across arms and ages, and higher with prior infection. For uninfected participants, Day 15 Omicron BA.1 GMTs were similar across Omicron-containing vaccine arms (3724-4561) and higher than Prototype (1,997 [95%CI:1,482-2,692]). The Omicron BA.1 monovalent and Omicron BA.1+Prototype vaccines induced a geometric mean ratio (GMR) to Prototype for Omicron BA.1 of 2.03 (97.5%CI:1.37-3.00) and 1.56 (97.5%CI:1.06-2.31), respectively. A subset of samples from uninfected participants in four arms were also tested in a different laboratory at Day 15 for neutralizing antibody titers to D614G and Omicron subvariants BA.1, BA.2.12.2 and BA.4/BA.5. Omicron BA.4/BA.5 GMTs were approximately one third BA.1 GMTs (Prototype 517 [95%CI:324-826] vs. 1503 [95%CI:949-2381]; Omicron BA.1+Beta 628 [95%CI:367-1,074] vs. 2125 [95%CI:1139-3965]; Omicron BA.1+Delta 765 [95%CI:443-1,322] vs. 2242 [95%CI:1218-4128] and Omicron BA.1+Prototype 635 [95%CI:447-903] vs. 1972 [95%CI:1337-2907). Conclusions: Higher Omicron BA.1 titers were observed with Omicron-containing vaccines compared to Prototype vaccine and titers against Omicron BA.4/BA.5 were lower than against BA.1 for all candidate vaccines. Clinicaltrials.gov: NCT05289037

SARS-CoV-2 Omicron Neutralization After Heterologous Vaccine Boosting (preprint)

As part of an ongoing study assessing homologous and heterologous booster vaccines, following primary EUA series, we assessed neutralization of D614G and Omicron variants prior to and 28 days after boost. Subset analysis was done in six combinations (N = 10/group): four homologous primary-booster combinations included mRNA-1273 two-dose priming followed by boosting with 100-g or 50-g mRNA-1273, Ad26.COV2.S single-dose priming followed by Ad26.COV2.S booster and BNT162b2 two-dose priming followed by BNT162b2 boosting; and two heterologous primary-booster combinations: BNT162b2 followed by Ad26.COV2.S and Ad26.COV2.S followed by BNT162b2. Neutralizing antibody (Nab) titers to D614G on the day of boost (baseline) were detected in 85-100% of participants, with geometric mean titers (GMT) of 71-343 in participants who received an mRNA vaccine series versus GMTs of 35-41 in participants primed with Ad26.OV2.S. Baseline NAb titers to Omicron were detected in 50-90% of participants who received an mRNA vaccine series (GMT range 12.8-24.5) versus 20-25% among participants primed with Ad26.COV2.S. The booster dose increased the neutralizing GMT in most combinations to above 1000 for D614G and above 250 for Omicron by Day 29. Homologous prime-boost Ad26.COV2.S had the lowest NAb on Day 29 (D614G GMT 128 and Omicron GMT 45). Results were similar between age groups. Most homologous and heterologous boost combinations examined will increase humoral immunity to the Omicron variant.

Booster of mRNA-1273 Vaccine Reduces SARS-CoV-2 Omicron Escape from Neutralizing Antibodies (preprint)

Data obtained on SARS-CoV-2 variant Omicron suggest that Omicron poses an increased risk of symptomatic breakthrough infections in people who receive only 2 doses of mRNA-1273. Administration of a booster mRNA vaccine may substantially reduce this risk.

Heterologous SARS-CoV-2 Booster Vaccinations: Preliminary Report (preprint)

Background: While Coronavirus disease 2019 (Covid-19) vaccines are highly effective, breakthrough infections are occurring. Booster vaccinations have recently received emergency use authorization (EUA) for certain populations but are restricted to homologous mRNA vaccines. We evaluated homologous and heterologous booster vaccination in persons who had received an EUA Covid-19 vaccine regimen. Methods: In this phase 1/2 open-label clinical trial conducted at ten U.S. sites, adults who received one of three EUA Covid-19 vaccines at least 12 weeks prior to enrollment and had no reported history of SARS-CoV-2 infection received a booster injection with one of three vaccines (Moderna mRNA-1273 100-mcg, Janssen Ad26.COV2.S 5x1010 virus particles, or Pfizer-BioNTech BNT162b2 30-mcg; nine combinations). The primary outcomes were safety, reactogenicity, and humoral immunogenicity on study days 15 and 29. Results: 458 individuals were enrolled: 154 received mRNA-1273, 150 received Ad26.CoV2.S, and 154 received BNT162b2 booster vaccines. Reactogenicity was similar to that reported for the primary series. Injection site pain, malaise, headache, and myalgia occurred in more than half the participants. Booster vaccines increased the neutralizing activity against a D614G pseudovirus (4.2-76-fold) and binding antibody titers (4.6-56-fold) for all combinations; homologous boost increased neutralizing antibody titers 4.2-20-fold whereas heterologous boost increased titers 6.2-76-fold. Day 15 neutralizing and binding antibody titers varied by 28.7-fold and 20.9-fold, respectively, across the nine prime-boost combinations. Conclusion: Homologous and heterologous booster vaccinations were well-tolerated and immunogenic in adults who completed a primary Covid-19 vaccine regimen at least 12 weeks earlier.