Antigenic and virological properties of an H3N2 variant that will likely dominate the 2021-2022 Northern Hemisphere influenza season

Influenza viruses have circulated at very low levels during the COVID-19 pandemic, and population immunity against these viruses is low. Influenza virus cases have been increasing in the Northern Hemisphere involving an H3N2 strain (3C.2a1b.2a2) with a hemagglutinin (HA) that has several substitutions relative to the 2021-2022 H3N2 vaccine strain. Here, we show that one of these substitutions eliminates a key glycosylation site on HA and alters sialic acid binding. Using glycan array profiling, we show that the 3C.2a1b.2a2 H3 maintains binding to an extended bi-antennary sialoside and replicates to high titers in human airway cells. We found that antibodies elicited by the 2021-2022 Northern Hemisphere influenza vaccine poorly neutralize the new H3N2 strain. Together, these data indicate that 3C.2a1b.2a2 H3N2 viruses efficiently replicate in human cells and could potentially cause an antigenic mismatch if they continue to circulate at high levels during the 2021-2022 influenza season.

AddaVax Formulated with PolyI:C as a Potential Adjuvant of MDCK-based Influenza Vaccine Enhances Local, Cellular, and Antibody Protective Immune Response in Mice

Poor immune responses to inactivated influenza vaccine can be improved by effective and safe adjuvants to increase antibody titers and cellular protective response. In our study, AddaVax and PolyI:C combined adjuvant (AP adjuvant) were used for influenza vaccine development. After immunizing BALB/c mice and Wistar rats intramuscularly, Split inactivated H3N2 vaccine adjuvanted with AP elicited higher serum hemagglutination-inhibition antibodies and IgG titers. We demonstrated that AP induced a transient innate immune cytokines production at the injection site, induced H3N2 uptake by DCs, increased recruitment of monocytes and DCs in LNs, and promoted H3N2 vaccine migration; AP facilitated vaccines to induce a vigorous adaptive immune response. Besides, AP showed good safety as shown by lymph nodes (LNs) size, spleens index of BALB/c mice, and weight changes and C-reaction protein level of BALB/c mice and Wistar rats after repeated administration of high-dose vaccine with or without adjuvant. These findings indicate that AP is a potential novel adjuvant and can be used as a safe and effective adjuvant for MDCK-based influenza inactivated vaccine to induce cellular and antibody protective response.

Influenza A/Singapore (H3N2) component vaccine in systemic lupus erythematosus: A distinct pattern of immunogenicity

Introduction Influenza A (H3N2) virus is the most important cause of seasonal influenza morbidity and mortality in the last 50 years, surpassing the impact of H1N1. Data assessing immunogenicity and safety of this virus component are lacking in systemic lupus erythematosus (SLE) and restricted to small reports with other H3N2 strains. Objective This study aims to evaluate short-term immunogenicity and safety of influenza A/Singapore (H3N2) vaccine in SLE. Methods 81 consecutive SLE patients and 81 age- and sex-matched healthy controls (HC) were vaccinated with the influenza A/Singapore/INFIMH-16-0019/2016(H3N2)-like virus. Seroprotection (SP) and seroconversion (SC) rates, geometric mean titers(GMT), and factor increase in GMT(FI-GMT) and adverse events were assessed before and 4 weeks post-vaccination. Disease activity and therapies were also evaluated. Results Before immunization, SLE and HC groups had high SP rates (89% vs 77%, p = 0.061) and elevated GMT titer with higher levels in SLE (129.1(104.1–154.1) vs 54.8(45.0–64.6), p < 0.001). Frequency of two previous years’ influenza vaccination was high and comparable in SLE and HC (89% vs 90%, p = 1.000). Four weeks post-vaccination, median GMT increased for both groups and remained higher in SLE compared to HC (239.9(189.5–290.4) vs 94.5(72.6–116.4), p < 0.0001) with a comparable FI-GMT (2.3(1.8–2.9) vs 1.9(1.5-2.3), p = 0.051). SC rates were low and comparable for both groups (16% vs 11%, respectively, p = 0.974). Disease activity scores remained stable throughout the study ( p = 1.000) and severe adverse events were not identified. Conclusion Influenza A/Singapore (H3N2) vaccine has an adequate safety profile. The distinct immunogenicity pattern from other influenza A components characterized by a remarkably high pre- and post-vaccination SP rate and high GMT levels may be associated with previous influenza A vaccination. ( www.clinicaltrials.gov , NCT03540823).

Comparison of the neuraminidase antigenicity in recently circulating influenza A and vaccine viruses

Neuraminidase (NA or N) antigens in circulating influenza viruses are not extensively evaluated for vaccine strain selection like hemagglutinin (HA or H) even though viral-based influenza vaccines include the recommended strain NA in varying amounts. As NA can also elicit a protective response, we assessed the antigenic similarity of the NAs from human H1N1 and H3N2 viruses that were prevalent between September 2019 to December 2020 to NAs from several recently recommended vaccine strains. To eliminate the dependence on isolates, the enzyme-linked lectin assay for analyzing NA antigenicity was performed with reverse genetic viruses carrying the same HA. Our results show that ferret antisera against NAs from the recommended H1N1 and H3N2 vaccine strains for the 2020-21 northern hemisphere influenza season recognize and inhibit the most prevalent circulating N1s and N2s, suggesting the NAs from the influenza A vaccine and circulating strains are antigenically similar. Comparisons of the recent N2s also revealed a bias in the reactivity of NA antisera from the egg and cell-based H3N2 vaccine strains due to a C-terminal substitution, indicating the C-terminus can influence N2 antigenicity and should receive consideration during the H3N2 strain selection.

Low Influenza Vaccine Effectiveness Against A(H3N2)-Associated Hospitalizations in 2016–2017 and 2017–2018 of the Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN)

Background The 2016–2017 and 2017–2018 influenza seasons were notable for the high number of hospitalizations for influenza A(H3N2) despite vaccine and circulating strain match. Methods We evaluated vaccine effectiveness (VE) against hospitalization in the test-negative HAIVEN study. Nasal-throat swabs were tested by quantitative reverse transcription polymerase chain reaction (RT-PCR) for influenza and VE was determined based on odds of vaccination by generalized estimating equations. Vaccine-specific antibody was measured in a subset of enrollees. Results A total of 6129 adults were enrolled from 10 hospitals. Adjusted VE against A(H3N2) was 22.8% (95% confidence interval [CI], 8.3% to 35.0%), pooled across both years and 49.4% (95% CI, 34.3% to 61.1%) against B/Yamagata. In 2017–2018, the A(H3N2) VE point estimate for the cell-based vaccine was 43.0% (95% CI, −36.3% to 76.1%; 56 vaccine recipients) compared to 24.0% (95% CI, 3.9% to 39.9%) for egg-based vaccines. Among 643 with serology data, hemagglutinin antibodies against the egg-based A(H3N2) vaccine strain were increased in influenza-negative individuals. Conclusions Low VE for the A/Hong Kong/4801/2014 vaccine virus in both A(H3N2) seasons emphasizes concerns for continued changes in H3N2 antigenic epitopes, including changes that may impact glycosylation and ultimately reduce VE.

Differential Antibody Recognition of H3N2 Vaccine and Seasonal Influenza Virus Strains Based on Age, Vaccine Status, and Sex in the 2017–2018 Season

Background An antigenic mismatch between the vaccine and circulating H3N2 strains was hypothesized to contribute to the severity of the 2017–2018 season in North America. Methods Serum and nasal washes were collected from influenza positive and negative patients during the 2017–2018 season to determine neutralizing antibody (nAb) titers and for influenza virus sequencing, respectively. Results The circulating and vaccine H3N2 virus strains were different clades, with the vaccine strain being clade 3C.2a and the circulating viruses being 3C.2a2 or 3C.3a. At enrollment, both the H3N2 negative and positive patients had greater nAb titers to the egg-adapted vaccine virus compared to the cell-grown vaccine but the H3N2-negative population had significantly greater titers to the circulating 3C.2a2. Among H3N2-positive patients, vaccination, younger age, and female sex were associated with greater nAb responses to the egg-adapted vaccine H3N2 virus but not to the cell-grown vaccine or circulating viruses. Conclusions For the 2017–2018 circulating viruses, mutations introduced by egg adaptation decreased vaccine efficacy. No increased protection was afforded by vaccination, younger age, or female sex against 2017–2018 circulating H3N2 viruses.

Influenza Vaccine Effectiveness by A(H3N2) Phylogenetic Subcluster and Prior Vaccination History: 2016–2017 and 2017–2018 Epidemics in Canada

Background The influenza A(H3N2) vaccine was updated from clade 3C.3a in 2015–2016 to 3C.2a for 2016–2017 and 2017–2018. Circulating 3C.2a viruses showed considerable hemagglutinin glycoprotein diversification and the egg-adapted vaccine also bore mutations. Methods Vaccine effectiveness (VE) in 2016–2017 and 2017–2018 was assessed by test-negative design, explored by A(H3N2) phylogenetic subcluster and prior season’s vaccination history. Results In 2016–2017, A(H3N2) VE was 36% (95% confidence interval [CI], 18%–50%), comparable with (43%; 95% CI, 24%–58%) or without (33%; 95% CI, −21% to 62%) prior season’s vaccination. In 2017–2018, VE was 14% (95% CI, −8% to 31%), lower with (9%; 95% CI, −18% to 30%) versus without (45%; 95% CI, −7% to 71%) prior season’s vaccination. In 2016–2017, VE against predominant clade 3C.2a1 viruses was 33% (95% CI, 11%–50%): 18% (95% CI, −40% to 52%) for 3C.2a1a defined by a pivotal T135K loss of glycosylation; 60% (95% CI, 19%–81%) for 3C.2a1b (without T135K); and 31% (95% CI, 2%–51%) for other 3C.2a1 variants (with/without T135K). VE against 3C.2a2 viruses was 45% (95% CI, 2%–70%) in 2016–2017 but 15% (95% CI, −7% to 33%) in 2017–2018 when 3C.2a2 predominated. VE against 3C.2a1b in 2017–2018 was 37% (95% CI, −57% to 75%), lower at 12% (95% CI, −129% to 67%) for a new 3C.2a1b subcluster (n = 28) also bearing T135K. Conclusions Exploring VE by phylogenetic subcluster and prior vaccination history reveals informative heterogeneity. Pivotal mutations affecting glycosylation sites, and repeat vaccination using unchanged antigen, may reduce VE.

Predominance of a Drifted Influenza A (H3N2) Clade and Its Association with Age-Specific Influenza Vaccine Effectiveness Variations, Influenza Season 2018–2019

Background: Influenza A (H3N2) clade 3C.3a was the predominant influenza virus in Israel throughout the 2018-2019 season, constituting a drift from the influenza A (H3N2) vaccine. We estimated the end-of season vaccine effectiveness (VE) by age, among community patients with influenza-like illness (ILI), considering the hemagglutinin (HA) gene mutations and amino acid substitutions of influenza A (H3N2) viruses detected. Methods: Nose-throat samples were analyzed for the presence of influenza virus, type/subtype, and HA gene sequence. HA gene sequences and amino acid substitutions were compared to the influenza A/Singapore/INFIMH-16-0019/2016 (H3N2)-like 2018-2019 vaccine virus, and a phylogenetic tree was generated. Influenza VE against influenza A (H3N2) was estimated using the test-negative design. VE was estimated by age group and by 15 year moving age intervals. Results: In total, 90% of the influenza A (H3N2) viruses belonged to the 3C.3a clade, constituting a unique situation in the northern hemisphere. Adjusted all-age influenza A (H3N2) VE was −3.5% (95% CI: −51.2 to 29.1). Although adjusted VEs were very low among infants, children, and young adults, a VE of 45% (95% CI: −19.2 to 74.6) was estimated among adults aged ≥45 years old. Conclusions: The higher VE point estimates among older adults may be related to previous exposure to similar influenza viruses.

Antigenic assessment of the H3N2 component of the 2019-2020 Northern Hemisphere influenza vaccine

The 2019-2020 Northern Hemisphere influenza vaccine includes antigens from 3c3.A H3N2 viruses; however, over half of circulating H3N2 viruses belong to subclade 3c2.A1b. Here, we analyzed antibody responses elicited by the egg-adapted 3c3.A H3N2 vaccine strain in ferrets and humans. We found that this vaccine strain elicits antibodies that have reduced reactivity to a wild-type 3c3.A strain and very limited reactivity to 3c2.A strains, including the currently circulating 3c2.A1b strain.