Effects of boosted mRNA and adenoviral-vectored vaccines on immune responses to omicron BA.1 and BA.2 following the heterologous CoronaVac/AZD1222 vaccination

Impact of Prior COVID-19 Immunization and/or Prior Infection on Immune Responses and Clinical Outcomes

Cellular and humoral immunity exhibit dynamic adaptation to the mutating SARS-CoV-2 virus. It is noteworthy that immune responses differ significantly, influenced by whether a patient has received vaccination or whether there is co-occurrence of naturally acquired and vaccine-induced immunity, known as hybrid immunity. The different immune reactions, conditional on vaccination status and the viral variant involved, bear implications for inflammatory responses, patient outcomes, pathogen transmission rates, and lingering post-COVID conditions. Considering these developments, we have performed a review of recently published literature, aiming to disentangle the intricate relationships among immunological profiles, transmission, the long-term health effects post-COVID infection poses, and the resultant clinical manifestations. This investigation is directed toward understanding the variability in the longevity and potency of cellular and humoral immune responses elicited by immunization and hybrid infection.

Second Boost of Omicron SARS-CoV-2 S1 Subunit Vaccine Induced Broad Humoral Immune Responses in Elderly Mice

Currently approved COVID-19 vaccines prevent symptomatic infection, hospitalization, and death from the disease. However, repeated homologous boosters, while considered a solution for severe forms of the disease caused by new SARS-CoV-2 variants in elderly individuals and immunocompromised patients, cannot provide complete protection against breakthrough infections. This highlights the need for alternative platforms for booster vaccines. In our previous study, we assessed the boost effect of the SARS-CoV-2 Beta S1 recombinant protein subunit vaccine (rS1Beta) in aged mice primed with an adenovirus-based vaccine expressing SARS-CoV-2-S1 (Ad5.S1) via subcutaneous injection or intranasal delivery, which induced robust humoral immune responses (1). In this follow-up study, we demonstrated that a second booster dose of a non-adjuvanted recombinant Omicron (BA.1) S1 subunit vaccine with Toll-like receptor 4 (TLR4) agonist RS09 (rS1RS09OM) was effective in stimulating strong S1-specific immune responses and inducing significantly high neutralizing antibodies against the Wuhan, Delta, and Omicron variants in 100-week-old mice. Importantly, the second booster dose elicits cross-reactive antibody responses, resulting in ACE2 binding inhibition against the spike protein of SARS-CoV-2 variants, including Omicron (BA.1) and its subvariants. Interestingly, the levels of IgG and neutralizing antibodies correlated with the level of ACE2 inhibition in the booster serum samples, although Omicron S1-specific IgG level showed a weaker correlation compared to Wuhan S1-specific IgG level. Furthermore, we compared the immunogenic properties of the rS1 subunit vaccine in young, middle-aged, and elderly mice, resulting in reduced immunogenicity with age, especially an impaired Th1-biased immune response in aged mice. Our findings demonstrate that the new variant of concern (VOC) rS1 subunit vaccine as a second booster has the potential to offer cross-neutralization against a broad range of variants and to improve vaccine effectiveness against newly emerging breakthrough SARS-CoV-2 variants in elderly individuals who were previously primed with the authorized vaccines.

Durability of immune response against omicron BA.2 and BA.4/5 and T cell responses after boosting with mRNA and adenoviral vector-based vaccines following heterologous CoronaVac/ChAdOx-1nCov-19 vaccination

Heterologous vaccination with inactivated vaccine followed by adenoviral vector-based vaccine has shown superiority in enhancing immune response compared to homologous primary series. However, data comparing immunity decline after a third booster following heterologous CoronaVac/ChAdOx-1nCov-19 has been limited. Here, we assessed neutralizing activity against omicron variant and T cell response at 3 months monitoring in 96 individuals who received ChAdOx-1nCov-19, BNT162b2, or mRNA-1273 as a third dose following heterologous CoronaVac/ChAdOx-1nCov-19. Comparing the antibody levels at 3 and 1 month(s) after the third booster, the results showed a persistence of anti-RBD IgG in all vaccine regimens, with the IgG level waning slower in the ChAdOx-1nCov-19 boosted group (geometric mean ratio (GMR): 0.64 (95%CI: 0.59-0.70)) compared to the BNT162b2 (0.34 (95%CI:0.31-0.38)) and mRNA-1273 boosted groups (0.32 (95%CI: 0.29-0.36)). Neutralizing activity against omicron BA.2 and BA.4/5 dropped by 1.2 to 1.5-fold but remained detectable, with the highest level observed in the mRNA-1273 group, followed by BNT162b2 and ChAdOx-1nCov-19 groups, respectively. Furthermore, the number of individuals with T cell reactivity decreased in BNT162b2 and mRNA-1273 groups, while it increased in ChAdOx-1nCov-19 group at 3-month post-boost compared to 1 month. Data on the durability of immune response could help comprehensively optimize the booster vaccine strategy.

Safety and Efficacy of a Third Dose of the BNT162b2 Vaccine in Liver-Transplanted and Healthy Adolescents

Objectives

According to our previous study, the 2-dose-BNT162b2 vaccination is less effective against the Omicron variant. This study aimed to assess the safety and efficacy of a 3-dose-BNT162b2 vaccination in liver-transplanted (LT) and healthy adolescents.

Methods

LT and healthy adolescents who met the inclusion criteria received a third dose of the BNT162b2 vaccine (30 µg). Antireceptor-binding domain immunoglobulin and T-cell-specific responses to severe acute respiratory syndrome coronavirus 2 spike peptides were assessed 3 months before the third dose (Visit -1) and 0 (Visit 0), 1 (Visit 1), and 2 months (Visit 2) after the third dose. Antinucleocapsid immunoglobulin and neutralizing antibodies were assessed at Visits 0 and 1. Adverse events (AEs) were monitored.

Results

Eleven LT and 14 healthy adolescents aged 14.64 (13.2, 15.7) years (44.2% male) had antireceptor-binding domain immunoglobulin geometric mean titers of 1412.47 (95% confidence interval [CI], 948.18-2041.11) and 1235.79 (95% CI, 901.07-1705.73) U/mL at Visit -1 but increased to 38 587.76 (95% CI, 24 628.03-60 460.18) and 29 222.38 (95% CI, 16 291.72-52 401.03) U/mL (P < 0.05) at Visit 1, respectively. This was consistent with neutralizing antibodies (42.29% and 95.37% vs 44.65% and 91.68%, P < 0.001) and interferon-γ-secreting cells in LT and healthy adolescents at Visit 0 versus Visit 1, respectively. For serious AEs, an LT girl with autoimmune overlap syndrome died 5 months postvaccination from acute liver failure.

Conclusions

In both LT and healthy adolescents, humoral and cellular immune responses were high after the 3-dose-BNT162b2 vaccination. However, serious AEs were suspected in LT adolescents with autoimmune diseases.

Hybrid Immunity Results in Enhanced and More Sustained Antibody Responses after the Second Sinovac-CoronaVac Dose in a Brazilian Cohort: DETECTCoV-19 Cohort

We measured anti-SARS-CoV-2 antibody responses before and after CoronaVac (inactivated) vaccination in a case-control study performed in CoronaVac-immunized individuals participating in a longitudinal prospective study of adults in Manaus (DETECTCoV-19). Antibody responses were measured by standard serological immunoassays. Peak anti-S-RBD and neutralizing RBD-ACE2 blocking antibody responses after two doses of CoronaVac vaccine were similar in vaccine breakthrough cases (n = 9) and matched controls (n = 45). Individuals with hybrid immunity resulting from prior SARS-CoV-2 infection followed by vaccination (n = 22) had elevated levels of anti-N, anti-S-RBD and RBD-ACE2 blocking antibodies after the second vaccine dose compared to infection-naïve individuals (n = 48). Post-vaccination SARS-CoV-2-specific antibody responses rapidly waned in infection-naïve individuals. Antibody responses wane after vaccination, making individuals susceptible to infection by SARS-CoV-2 variants. These findings support the need for booster doses after primary vaccination. Population antibody serosurveys provide critical information toward implementing optimal timing of booster doses.

Neutralizing antibodies against Omicron BA.5 among children with infection alone, vaccination alone, and hybrid immunity

OBJECTIVES

To assess the binding antibody response and strength of neutralization against Omicron BA.5 in serum samples from children with different antigen exposures (infection/vaccination) and hybrid immunity.

METHODS

This study recruited children aged 5-7 years. All samples were tested for anti-nucleocapsid immunoglobulin (Ig)G, anti-receptor binding domain (RBD) IgG, and total anti-RBD Ig. Neutralizing antibodies (nAbs) against Omicron BA.5 were determined using a focus reduction neutralization test.

RESULTS

A total of 196 serum samples from unvaccinated children with infection (n = 57), vaccination alone (n = 71), and hybrid immunity (n = 68). Our results showed that 90% of the samples from children with hybrid immunity, 62.2% from two-dose vaccination, and 48% from Omicron infection alone had detectable nAbs against Omicron BA.5. The highest neutralizing titer was observed in infection plus two-dose vaccination, which reached 6.3-fold increase, whereas nAb titers in two-dose vaccination was comparable to Omicron-infected sera. However, sera from pre-Omicron infection and single-dose vaccination failed to neutralize Omicron BA.5; although, the total anti-RBD Ig were comparable with Omicron-infected sera.

CONCLUSION

This result highlights that hybrid immunity provided cross-reactive antibodies to neutralize Omicron BA.5 compared with either vaccination or infection alone. The finding emphasizes the importance of vaccination in unvaccinated children who are infected with pre-Omicron or Omicron variants.

SARS-CoV-2 Antibody Dynamics after COVID-19 Vaccination and Infection: A Real-World Cross-Sectional Analysis

The Coronavirus disease 2019 (COVID-19) pandemic, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), continues to surge despite the widespread use of vaccination. In Thailand, more than 77% and 39% of the population received two doses and three doses of COVID-19 vaccines as of December 2022, respectively. In addition, during the Omicron predominant period in 2022, more than 70% of Thai individuals have been infected. To gain comprehensive insight into SARS-CoV-2 antibody dynamics following vaccination or following vaccination and infection (hybrid immunity), we performed a cross-sectional analysis of sera samples from individuals who received COVID-19 vaccination and/or have been infected with COVID-19 in Thailand between January 2021 and December 2022. A total of 4126 samples were collected. Humoral immunity was evaluated by quantifying the immunoglobulin (including IgG, IgM, and IgA isotypes) specific to the SARS-CoV-2 receptor-binding domain (RBD) or Ig anti-RBD. The results showed that individuals who received two-dose vaccination alone had lower levels of Ig anti-RBD, which rapidly waned over time. To restore the waning antibody, a third dose vaccination is recommended for uninfected individuals who have only received 2 doses.

Pre-existing humoral immunity and CD4+ T cell response correlate with cross-reactivity against SARS-CoV-2 Omicron subvariants after heterologous prime-boost vaccination

BACKGROUND

Information regarding the heterologous prime-boost COVID vaccination has been fully elucidated. The study aimed to evaluate both humoral, cellular immunity and cross-reactivity against variants after heterologous vaccination.

METHODS

We recruited healthcare workers previously primed with Oxford/AstraZeneca ChAdOx1-S vaccines and boosted with Moderna mRNA-1273 vaccine boost to evaluate the immunological response. Assay used: anti-spike RBD antibody, surrogate virus neutralizing antibody and interferon-γ release assay.

RESULTS

All participants exhibited higher humoral and cellular immune response after the booster regardless of prior antibody level, but those with higher antibody level demonstrated stronger booster response, especially against omicron BA.1 and BA.2 variants. The pre-booster IFN-γ release by CD4⁺ T cells correlates with post-booster neutralizing antibody against BA.1 and BA.2 variant after adjustment with age and gender.

CONCLUSIONS

A heterologous mRNA boost is highly immunogenic. The pre-existing neutralizing antibody level and CD4⁺ T cells response correlates with post-booster neutralization reactivity against the Omicron variant.

Effects of Omicron Infection and Changes in Serum Antibody Response to Wild-Type, Delta, and Omicron After a Booster Dose With BNT163b2 Vaccine in Korean Healthcare Workers

BACKGROUND

Although the primary vaccine coverage rate for coronavirus disease 2019 (COVID-19) in South Korea has exceeded 80%, the coronavirus continues to spread, with reports of a rapid decline in vaccine effectiveness. South Korea is administering booster shots despite concerns about the effectiveness of the existing vaccine.

METHODS

Neutralizing antibody inhibition scores were evaluated in two cohorts after the booster dose. For the first cohort, neutralizing activity against the wild-type, delta, and omicron variants after the booster dose was evaluated. For the second cohort, we assessed the difference in neutralizing activity between the omicron infected and uninfected groups after booster vaccination. We also compared the effectiveness and adverse events (AEs) between homologous and heterologous booster doses for BNT162b2 or ChAdOx1 vaccines.

RESULTS

A total of 105 healthcare workers (HCWs) that were additionally vaccinated with BNT162b2 at Soonchunhyang University Bucheon Hospital were enrolled in this study. Significantly higher surrogate virus neutralization test (sVNT) inhibition (%) was observed for the wild-type and delta variants compared to sVNT (%) for the omicron after the booster dose (97%, 98% vs. 75%; P < 0.001). No significant difference in the neutralizing antibody inhibition score was found between variants in the BNT/BNT/BNT group (n = 48) and the ChA/ChA/BNT group (n = 57). Total AEs were not significantly different between the ChA/ChA/BNT group (85.96%) and the BNT/BNT group (95.83%; P = 0.11). In the second cohort with 58 HCWs, markedly higher sVNT inhibition to omicron was observed in the omicron-infected group (95.13%) compared to the uninfected group (mean of 48.44%; P < 0.001) after four months of the booster dose. In 41 HCWs (39.0%) infected with the omicron variant, no difference in immunogenicity, AEs, or effectiveness between homogeneous and heterogeneous boosters was observed.

CONCLUSION

Booster vaccination with BNT162b2 was significantly less effective for the neutralizing antibody responses to omicron variant compared to the wild-type or delta variant in healthy population. Humoral immunogenicity was sustained significantly high after 4 months of booster vaccine in the infected population after booster vaccination. Further studies are needed to understand the characteristics of immunogenicity in these populations.

The Fourth Dose of mRNA COVID-19 Vaccine Following 12 Different Three-Dose Regimens: Safety and Immunogenicity to Omicron BA.4/BA.5

The aim of this study is to investigate the reactogenicity and immunogenicity of the fourth dose using monovalent mRNA vaccines after different three-dose regimens and to compare the 30 µg BNT162b2 and 50 µg mRNA-1273 vaccines. This prospective cohort study was conducted between June and October 2022. The self-recorded reactogenicity was evaluated on the subsequent 7 days after a fourth dose. The binding and neutralizing activity of antibodies against the Omicron BA.4/5 variants were determined. Overall, 292 healthy adults were enrolled and received BNT162b2 or mRNA-1273. Reactogenicity was mild to moderate and well tolerated after a few days. Sixty-five individuals were excluded. Thus, 227 eligible individuals received a fourth booster dose of BNT162b2 (n = 109) and mRNA-1273 (n = 118). Most participants, regardless of the type of previous three-dose regimens, elicited a significantly high level of binding antibodies and neutralizing activity against Omicron BA.4/5 28 days after a fourth dose. The neutralizing activity against Omicron BA.4/5 between the BNT162b2 (82.8%) and mRNA-1273 (84.2%) groups was comparable with a median ratio of 1.02. This study found that the BNT162b2 and mRNA-1273 vaccines can be used as a fourth booster dose for individuals who were previously immunized with any prior three-dose mix-and-match COVID-19 vaccine regimens.

Dynamics of disease characteristics and viral RNA decay in patients with asymptomatic and mild infections during the Omicron wave in Shanghai, China: A retrospective cohort study

OBJECTIVES

Asymptomatic infections and mild diseases were more common during the Omicron outbreak in Shanghai, China in 2022. This study aimed to assess the characteristics and viral RNA decay between patients with asymptomatic and mild infections.

METHODS

A total of 55,111 patients infected with SARS-CoV-2 who were quarantined in the National Exhibition & Convention Center (Shanghai) Fangcang shelter hospital within 3 days after diagnosis from April 9 to May 23, 2022 were enrolled. The kinetics of cycle threshold (Ct) values of reverse transcription-polymerase chain reaction were assessed. The influencing factors for disease progression and the risk factors for the viral RNA shedding time (VST) were investigated.

RESULTS

On admission, 79.6% (43,852/55,111) of the cases were diagnosed with asymptomatic infections, and 20.4% were mild diseases. However, 78.0% of initially asymptomatic subjects developed mild diseases at the follow-up. The final proportion of asymptomatic infections was 17.5%. The median time of symptom onset, the duration of symptoms, and the VST were 2 days, 5 days, and 7 days, respectively. Female, age 19-40 years, underlying comorbidities with hypertension and diabetes, and vaccination were associated with higher risks of progressing to mildly symptomatic infections. In addition, mildly symptomatic infections were found to be associated with prolonged VST compared with asymptomatic infections. However, the kinetics of viral RNA decay and dynamics of Ct values were similar among asymptomatic subjects, patients with asymptomatic-to-mild infection, and patients with mild infection.

CONCLUSION

A large proportion of initially diagnosed asymptomatic Omicron infections is in the presymptomatic stage. The Omicron infection has a much shorter incubation period and VST than previous variants. The infectivity of asymptomatic infections and mildly symptomatic infections with Omicron is similar.

Adenoviral Vector-Based Vaccine Platform for COVID-19: Current Status

The coronavirus disease (COVID-19) breakout had an unimaginable worldwide effect in the 21st century, claiming millions of lives and putting a huge burden on the global economy. The potential developments in vaccine technologies following the determination of the genetic sequence of SARS-CoV-2 and the increasing global efforts to bring potential vaccines and therapeutics into the market for emergency use have provided a small bright spot to this tragic event. Several intriguing vaccine candidates have been developed using recombinant technology, genetic engineering, and other vaccine development technologies. In the last decade, a vast amount of the vaccine development process has diversified towards the usage of viral vector-based vaccines. The immune response elicited by such vaccines is comparatively higher than other approved vaccine candidates that require a booster dose to provide sufficient immune protection. The non-replicating adenoviral vectors are promising vaccine carriers for infectious diseases due to better yield, cGMP-friendly manufacturing processes, safety, better efficacy, manageable shipping, and storage procedures. As of April 2022, the WHO has approved a total of 10 vaccines around the world for COVID-19 (33 vaccines approved by at least one country), among which three candidates are adenoviral vector-based vaccines. This review sheds light on the developmental summary of all the adenoviral vector-based vaccines that are under emergency use authorization (EUA) or in the different stages of development for COVID-19 management.

Omicron infection increases IgG binding to spike protein of predecessor variants

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission in India in 2020-2022 was driven predominantly by Wild (Wuhan-Hu-1 and D614G), Delta, and Omicron variants. The aim of this study was to examine the effect of infections on the humoral immune response and cross-reactivity to spike proteins of Wuhan-Hu-1, Delta, C.1.2., and Omicron. Residual archival sera (N = 81) received between January 2020 and March 2022 were included. Infection status was inferred by a positive SARS-CoV-2 RT-PCR and/or serology (anti-N and anti-S antibodies) and sequencing of contemporaneous samples (N = 18) to infer lineage. We estimated the levels and cross-reactivity of infection-induced sera including Wild, Delta, Omicron as well as vaccine breakthrough infections (Delta and Omicron). We found an approximately two-fold increase in spike-specific IgG antibody binding in post-Omicron infection compared with the pre-Omicron period, whilst the change in pre- and post-Delta infections were similar. Further investigation of Omicron-specific humoral responses revealed primary Omicron infection as an inducer of cross-reactive antibodies against predecessor variants, in spite of the weaker degree of humoral response compared to Wuhan-Hu-1 and Delta infection. Intriguingly, Omicron vaccine-breakthrough infections when compared with primary infections, exhibited increased humoral responses against RBD (7.7-fold) and Trimeric S (Trimeric form of spike protein) (34.6-fold) in addition to increased binding of IgGs towards previously circulating variants (4.2 - 6.5-fold). Despite Delta breakthrough infections showing a higher level of humoral response against RBD (2.9-fold) and Trimeric S (5.7-fold) compared to primary Delta sera, a demonstrably reduced binding (36%-49%) was observed to Omicron spike protein. Omicron vaccine breakthrough infection results in increased intensity of humoral response and wider breadth of IgG binding to spike proteins of antigenically-distinct, predecessor variants.

Safety and immunogenicity of a third dose of COVID-19 protein subunit vaccine (CovovaxTM) after homologous and heterologous two-dose regimens

OBJECTIVES

To report the safety and immunogenicity profile of a protein subunit vaccine (Covovax^TM) given as a third (booster) dose to individuals primed with different primary vaccine regimens.

METHODS

A third dose was administered to individuals with an interval range of 3-10 months after the second dose. The four groups were classified according to their primary vaccine regimens, including two-dose BBIBP-CorV, AZD1222, BNT162b2, and CoronaVac/AZD1222. Immunogenicity analysis was performed to determine binding antibodies, neutralizing activity, and the T-cell responses.

RESULTS

Overall, 210 individuals were enrolled and boosted with the Covovax^TM vaccine. The reactogenicity was mild to moderate. Most participants elicited a high level of binding and neutralizing antibody against Wild-type and Omicron variants after the booster dose. In participants who were antinucleocapsid immunoglobulin G-negative from all groups, a booster dose could elicit neutralizing activity to Wild-type and Omicron variants by more than 95% and 70% inhibition at 28 days, respectively. The Covovax^TM vaccine could elicit a cell-mediated immune response.

CONCLUSION

The protein subunit vaccine (Covovax^TM) can be proposed as a booster dose after two different priming dose regimens. It has strong immunogenicity and good safety profiles.

Selective IgA Deficiency May Be an Underrecognized Risk Factor for Severe COVID-19

SARS-CoV-2, the agent responsible for COVID-19, has wreaked havoc around the globe. Hundreds of millions of individuals have been infected and well over six million have died from COVID-19. Many COVID-19 survivors have ongoing physical and psychiatric morbidity, which will remain for the rest of their lives. Early in the pandemic, it became apparent that older individuals and those with comorbidities including obesity, diabetes mellitus, coronary artery disease, hypertension, and renal and pulmonary disease were at increased risk of adverse outcomes. It is also clear that some immunodeficient patients, such as those with innate or T cell-immune defects, are at greater risk from COVID-19. Selective IgA deficiency (sIgAD) is generally regarded as a mild disorder in which most patients are asymptomatic because of redundancy in protective immune mechanisms. Recent data indicate that patients with sIgAD may be at high risk of severe COVID-19. SARS-CoV-2 gains entry primarily through the upper respiratory tract mucosa, where IgA has a critical protective role. This may underlie the vulnerability of sIgAD patients to adverse outcomes from COVID-19. This perspective highlights the need for ongoing research into mucosal immunity to improve COVID-19 treatments for patients with sIgAD.

RNA Interference Approach Is a Good Strategy against SARS-CoV-2

COVID-19, caused by SARS-CoV-2, created a devastating outbreak worldwide and consequently became a global health concern. However, no verifiable, specifically targeted treatment has been devised for COVID-19. Several emerging vaccines have been used, but protection has not been satisfactory. The complex genetic composition and high mutation frequency of SARS-CoV-2 have caused an uncertain vaccine response. Small interfering RNA (siRNA)-based therapy is an efficient strategy to control various infectious diseases employing post-transcriptional gene silencing through the silencing of target complementary mRNA. Here, we designed two highly effective shRNAs targeting the conserved region of RNA-dependent RNA polymerase (RdRP) and spike proteins capable of significant SARS-CoV-2 replication suppression. The efficacy of this approach suggested that the rapid development of an shRNA-based therapeutic strategy might prove to be highly effective in treating COVID-19. However, it needs further clinical trials.

Challenges and developments in universal vaccine design against SARS-CoV-2 variants

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had become a global concern because of its unexpectedly high pathogenicity and transmissibility. SARS-CoV-2 variants that reduce the immune protection elicited from previous vaccination or natural infection raise challenges in controlling the spread of the pandemic. The development of universal vaccines against these variants seems to be a practical solution to alleviate the physical and economic effects caused by this disease, but it is hard to achieve. In this review, we describe the high mutation rate of RNA viruses and dynamic molecular structures of SARS-CoV-2 variants in several major neutralizing epitopes, trying to answer the question of why universal vaccines are difficult to design. Understanding the biological basis of immune evasion is crucial for combating these obstacles. We then summarize several advancements worthy of further study, including heterologous prime-boost regimens, construction of chimeric immunogens, design of protein nanoparticle antigens, and utilization of conserved neutralizing epitopes. The fact that some immunogens can induce cross-reactive immune responses against heterologous coronaviruses provides hints for universal vaccine development. We hope this review can provide inspiration to current universal vaccine studies.

Immunogenicity after a Third COVID-19 mRNA Booster in Solid Cancer Patients Who Previously Received the Primary Heterologous CoronaVac/ChAdOx1 Vaccine

No data regarding the efficacy of a third mRNA vaccine for solid cancer patients previously primed with the heterologous CoronoVac/ChAdOx1 vaccination implemented in Thailand during the shortage of vaccine supply are available. Forty-four cancer patients who previously received the heterologous CoronaVac-ChAdOx1 regimen were boosted with a third mRNA COVID vaccine, either BNT162b2 or mRNA-1273. Anti-RBD IgG was measured immediately before, two weeks after, and four weeks after the third dose. The antibody response was compared to 87 age- and gender-matched cancer patients who were primed with the homologous ChAdOx1/ChAdOx1 regimens. Post-third dose anti-RBD IgG levels significantly increased compared to pre-third dose levels. There was no statistical difference in post-third dose antibody titers or neutralization levels between these two primary series regimens. Treatment with chemotherapy was associated with a lower antibody response compared to endocrine therapy/biologics. Similar antibody levels were observed after a third booster with either BNT162b2 or mRNA-1273 following heterologous CoronaVac/ChAdOx1 vaccination. There was no statistical difference in the immune response following the third-dose vaccination between cancer patients and healthy individuals who received the same heterologous CoronaVac/ChAdOx1 vaccination. In conclusion, a similar degree of enhanced immunogenicity was observed after a third mRNA COVID-19 vaccination in solid cancer patients who previously received the heterologous CoronaVac/ChAdOx1 regimens.

Strong Correlations between the Binding Antibodies against Wild-Type and Neutralizing Antibodies against Omicron BA.1 and BA.2 Variants of SARS-CoV-2 in Individuals Following Booster (Third-Dose) Vaccination

This study examined the neutralizing activity and receptor-binding domain (RBD) antibody levels against wild-type and omicron BA.1 and BA.2 variants in individuals who received three doses of COVID-19 vaccination. The relationship between the anti-RBD IgG against wild-type and live virus neutralizing antibody titers against omicron BA.1 and BA.2 variants was examined. In total, 310 sera samples from individuals after booster vaccination (third-dose) were tested for specific IgG wild-type SARS-CoV-2 RBD and the omicron BA.1 surrogate virus neutralization test (sVNT). The live virus neutralization assay against omicron BA.1 and BA.2 was performed using the foci-reduction neutralization test (FRNT50). The anti-RBD IgG strongly correlated with FRNT50 titers against BA.1 and BA.2. Non-linear regression showed that anti-RBD IgG at the cut-off value ≥148 BAU/mL and ≥138 BAU/mL were related to the threshold for FRNT50 titers ≥20 against BA.1 and BA.2, respectively. A moderate correlation was observed between the sVNT and FRNT50 titers. At FRNT50 titers ≥20, the predicted sVNT for BA.1 and BA.2 was ≥10.57% and ≥11.52%, respectively. The study identified anti-RBD IgG and sVNT levels that predict detectable neutralizing antibodies against omicron variants. Assessment and monitoring of protective immunity support vaccine policies and will help identify optimal timing for booster vaccination.