Immunogenicity and reactogenicity of mRNA COVID-19 vaccine booster administered by intradermal or intramuscular route in Thai older adults (preprint)

Introduction: Intradermal (ID) vaccination may alleviate COVID-19 vaccine shortages and vaccine hesitancy due to systemic reactogenicity among older adults. Objectives: To compare the immunogenicity and reactogenicity of fractional ID and standard intramuscular (IM) booster vaccination of mRNA-1273 and BNT162b2 vaccines in older adults. Methods: Participants aged [≥]65 years who previously vaccinated with 2-dose ChAdOx1 were randomized to receive one of the four booster vaccinations: 0.1mL ID mRNA-1273, 0.5mL IM mRNA-1273, 0.1mL ID BNT162b2 and 0.3mL IM BNT162b2. Immunogenicity as measured by anti-receptor binding domain (anti-RBD) IgG against Wuhan, neutralising antibody (NAb) against Wuhan and Omicron BA.1, BA.2 and BA.4/5, and IFN{gamma}-producing cells. Local and systemic adverse effects (AEs) were self-reported via an electronic diary card. Results: Of the 210 participants enrolled, 70.5% were female and median age was 77.5 years (interquartile range (IQR): 71.0-84.0). Following the booster dose, both ID vaccination induced 37% lower levels of anti-RBD IgG than IM vaccination of the same vaccine. NAb against ancestral and Omicron BA.1 strains was highest following IM mRNA-1273 (1,718 and 617), followed by ID mRNA-1273 (1,212 and 318), IM BNT162b2 (713 and 230), and ID BNT162b2 (587 and 148), respectively. Spike-specific IFN{gamma} responses were similar or higher in the ID groups when compared with their respective IM groups. Vaccine delivery through ID route tended to have lower systemic AEs, although more local AEs reported in ID mRNA-1273 group. Conclusions: Fractional ID vaccination induced immunogenicity and reactogenicity comparable to IM and may be an alternative option for older people.

Comparison of antibody responses to SARS-CoV-2 variants in Australian children (preprint)

There is limited understanding of antibody responses in children across different SARS-CoV-2 variants. As part of an ongoing household cohort study, we assessed the antibody response among unvaccinated children infected with Wuhan, Delta or Omicron variants, as well as vaccinated children with breakthrough Omicron infection, using a SARS-CoV-2 S1-specific IgG assay and surrogate virus neutralisation test (sVNT). Most children infected with Delta (100%, 35/35) or Omicron (81.3%, 13/16) variants seroconverted by one month following infection. In contrast, 37.5% (21/56) children infected with Wuhan seroconverted, as previously reported. However, Omicron-infected children (GMC 46.4 BAU/ml; sVNT % inhibition: 16.3%) mounted a significantly lower antibody response than Delta (435.5 BAU/mL, sVNT=76.9%) or Wuhan (359.0 BAU/mL, sVNT=74.0%). Vaccinated children with breakthrough Omicron infection mounted the highest antibody response (2856 BAU/mL, sVNT=96.5%). Our findings suggest that despite a high seroconversion rate, Omicron infection in children results in lower antibody levels and function compared with Wuhan or Delta infection or with vaccinated children with breakthrough Omicron infection. Our data have important implications for public health measures and vaccination strategies to protect children.

Safety and Immunogenicity of Intradermal Administration of Fractional Dose CoronaVac(R), ChAdOx1 nCoV-19 and BNT162b2 as Primary Series Vaccination (preprint)

There is a limited supply of COVID-19 vaccines, with less than 20% of eligible populations in low- income countries having received one dose. Intradermal delivery of fractional dose vaccines is one way to improve global vaccine access, but no studies have reported data on intradermal delivery of COVID-19 primary series vaccination. We conducted a pilot study to examine the safety and immunogenicity of three intradermal primary series regimens - heterologous regimen of CoronaVac and ChAdOx1 (CoronaVac-ChAdOx1), homologous regimen of ChAdOx1 (ChAdOx1-ChAdOx1), and homologous regimen of BNT162b2 (BNT162b2-BNT162b2). Each dose was 1/5th or 1/6th of the standard dose. Two additional exploratory arms of intradermal vaccination for the second dose following an intramuscular first dose of ChAdOx1 and BNT162b2 were included. Intradermal vaccination was found to be immunogenic and safe. The antibody responses generated by the intradermal primary series were highest in the BNT162b2 arms. The anti-receptor binding domain (anti-RBD) IgG concentration following fractional dose intradermal vaccination was similar to that of standard dose intramuscular vaccination of the same regimen, except for BNT162b2. The BNT162b2 intradermal series generated a lower antibody concentration than the reference intramuscular series, despite generating the highest antibody concentration of all three intradermal primary series regimens. Neutralizing antibody responses against the SARS-CoV-2 ancestral strain were consistent with what was observed for anti-RBD IgG, with lower titers for SARS-CoV-2 variants. The FRNT50 titers were lowest against the omicron variant, being undetectable (GMT[≤]10) in about a quarter of study participants. T-cell responses against spike- and nucleocapsid-membrane-open reading frame proteins were also detected following intradermal vaccination. Adverse effects following intradermal vaccination were generally comparable with post-intramuscular vaccination effects. Taken together, our data suggest that intradermal vaccination using 1/5th or 1/6th of standard COVID-19 intramuscular vaccination dosing generates similar immune responses with tendency of lower systemic adverse reactions than intramuscular vaccination. Our findings have implications in settings where COVID-19 vaccines are in shortage.

Evaluation of the safety and immunogenicity of fractional intradermal COVID-19 vaccines as a booster: A pilot study (preprint)

Intradermal vaccination using fractional dosage of the standard vaccine dose is one strategy to improve access to COVID-19 immunization. We conducted a pilot study in healthy adults in Thailand to evaluate the safety and immunogenicity of intradermal administration of fractional dose of ChAdOx1 (1/5th of standard dosage) or BNT162b2 (1/6th of standard dosage) to individuals previously vaccinated (prime) with two-dose intramuscular CoronaVac, ChAdOx1 or BNT162b2. Following an initial immunogenicity exploratory phase for each vaccine combination group (N=10), a total of 135 participants (N=45 per group) were recruited to three groups (CoronaVac prime-intradermal BNT162b2 boost, CoronaVac prime-intradermal ChAdOx1 boost and ChAdOx1 prime-intradermal BNT162b2 boost) and their immunogenicity data compared to a previous cohort who received the same vaccine intramuscularly. Two weeks following booster vaccination, neutralizing antibodies against the delta variant were similar between intradermal and intramuscular vaccination. However, neutralizing antibodies against the omicron variant in the intradermal BNT162b2 boost groups were [~]6-fold lower, while the ChAdOx1 boost group was [~]5-fold higher compared to their respective vaccine regimen given intramuscularly. The intradermal booster significantly increased spike-specific T cell responses in all three groups from pre-booster levels. Local and systemic adverse reactions were milder in intradermal compared to intramuscular injections. Further studies are needed to evaluate the clinical relevance of these findings and the feasibility of administration of intradermal COVID-19 vaccines.

Virology and immune dynamics reveal high household transmission of ancestral SARS-CoV-2 strain (preprint)

Background: Household studies are crucial for understanding the transmission of SARS-CoV-2 infection, which may be underestimated from PCR testing of respiratory samples alone. We aim to combine assessment of household mitigation measures; nasopharyngeal, saliva and stool PCR testing; along with mucosal and systemic SARS-CoV-2 specific antibodies, to comprehensively characterise SARS-CoV-2 infection and transmission in households. Methods: Between March and September 2020, we obtained samples from 92 participants in 26 households in Melbourne, Australia, in a 4-week period following onset of infection with ancestral SARS-CoV-2 variants. Results: The secondary attack rate was 36% (24/66) when using nasopharyngeal swab (NPS) PCR positivity alone. However, when respiratory and non-respiratory samples were combined with antibody responses in blood and saliva, the secondary attack rate was 76% (50/66). SARS-CoV-2 viral load of the index case and household isolation measures were key factors that determine secondary transmission. In 27% (7/26) of households, all family members tested positive by NPS for SARS-CoV-2 and were characterised by lower respiratory Ct-values than low transmission families (Median 22.62 vs 32.91; IQR 17.06 to 28.67 vs 30.37 to 34.24). High transmission families were associated with enhanced plasma antibody responses to multiple SARS-CoV-2 antigens and the presence of neutralising antibodies. Three distinguishing saliva SARS-CoV-2 antibody features were identified according to age (IgA1 to Spike 1, IgA1 to nucleocapsid protein (NP), suggesting that adults and children generate distinct mucosal antibody responses during the acute phase of infection. Conclusion: Utilising respiratory and non-respiratory PCR testing, along with measurement of SARS-CoV-2 specific local and systemic antibodies, provides a more accurate assessment of infection within households and highlights some of the immunological differences in response between children and adults.

Immunogenicity and reactogenicity against the SARS-CoV-2 variants following heterologous primary series involving CoronaVac and ChAdOx1 and BNT162b2 plus heterologous BNT162b2 booster vaccination: An open-label randomized study in healthy Thai adults. (preprint)

We evaluated the immunogenicity and reactogenicity of heterologous COVID-19 primary series vaccination schedules. Participants were randomized to one of seven groups that received two-dose homologous BNT162b2 or heterologous combinations of CoronaVac, ChAdOx1 and BNT162b2, with 4 weeks interval. Of 210 participants, median age was 38 (19-60) years, 51% were female. The groups that received BNT162b2 as second dose induced the highest virus-specific IgG response against the ancestral strain [BNT162b2: geometric mean concentration (GMC) 2133-2249, 95%CI 1558 to 3055; ChAdOx1: 851-1201, 95%CI 649 to 1522; CoronaVac: 137-225, 95%CI 103-286 BAU/mL], neutralising antibodies (NAb) against Beta and Delta, and interferon gamma response. All groups induced low to negligible NAb against Omicron. A BNT162b2 booster (3rd dose) following heterologous CoronaVac and ChAdOx1 regimens induced >140-fold increase in NAb titres against Omicron. Our findings indicate that heterologous regimens using BNT162b2 as the second dose may be considered an alternative schedule to maximize immune response.

The immunogenicity and safety of different COVID-19 booster vaccination following CoronaVac or ChAdOx1 nCoV-19 primary series (preprint)

The appropriate COVID-19 booster vaccine following inactivated or adenoviral vector COVID-19 vaccination is unclear. We evaluated the safety and immunogenicity of different booster vaccines, inactivated (BBIBP-CorV), chimpanzee adenoviral vector (ChAdOx1), or mRNA (BNT162b2 at full (30 µg), or half (15 µg) dose) in healthy adults who received 2-dose primary series of either inactivated vaccine (CoronaVac) or ChAdOx1 8-12 weeks earlier. Overall, the adverse events for all booster vaccines were mild and moderate. Two weeks post-booster dose, the neutralising antibody titres against Delta variant in CoronaVac-prime and ChAdOx1-prime were highest with for 30µg-BNT162b2 (411 vs 470) and 15µg-BNT162b2 (499 vs 358); followed by ChAdOx1 (271 vs 69), and BBIBP-CorV (61.3 vs 49). BNT162b2 also induced higher interferon gamma response. Heterologous COVID-19 boosting vaccination with BNT162b2 is the most immunogenic following CoronaVac or ChAdOx1 primary series. A lower dose BNT162b2 may be used as booster in settings with limited vaccine supply.

The immunogenicity and safety of different COVID-19 booster vaccination following CoronaVac or ChAdOx1 nCoV-19 primary series (preprint)

The appropriate COVID-19 booster vaccine following inactivated or adenoviral vector COVID-19 vaccination is unclear. We evaluated the safety and immunogenicity of different booster vaccines, inactivated (BBIBP-CorV), chimpanzee adenoviral vector (ChAdOx1), or mRNA (BNT162b2 at full (30 g), or half (15 g) dose) in healthy adults who received 2-dose primary series of either inactivated vaccine (CoronaVac) or ChAdOx1 8-12 weeks earlier. Overall, the adverse events for all booster vaccines were mild and moderate. Two weeks post-booster dose, the neutralising antibody titres against Delta variant in CoronaVac-prime and ChAdOx1-prime were highest with for 30g-BNT162b2 (411 vs 470) and 15g-BNT162b2 (499 vs 358); followed by ChAdOx1 (271 vs 69), and BBIBP-CorV (61.3 vs 49). BNT162b2 also induced higher interferon gamma response. Heterologous COVID-19 boosting vaccination with BNT162b2 is the most immunogenic following CoronaVac or ChAdOx1 primary series. A lower dose BNT162b2 may be used as booster in settings with limited vaccine supply.

Reduced seroconversion in children compared to adults with mild COVID-19 (preprint)

Importance The immune response in children with SARS-CoV-2 infection is not well understood. Objective To compare seroconversion in children and adults with non-hospitalized (mild) SARS-CoV-2 infection and to understand the factors that influence this. Design Participants were part of a household cohort study of SARS-CoV-2 infection. Weekly nasopharyngeal/throat swabs and blood samples were collected during the acute and convalescent period following PCR diagnosis for analysis. Setting Participants were recruited at the Royal Children’s Hospital, Melbourne, Australia between May and October 2020. Participants Those who had a SARS-CoV-2 PCR-positive nasal/throat swab. Main outcomes and measures SARS-CoV-2 antibody and cellular responses in children and adults. Seroconversion was defined by seropositivity in all three serological assays. Results Among 108 SARS-CoV-2 PCR-positive participants, 57 were children (median age: 4, IQR 2-10) and 51 were adults (median age: 37, IQR 34-45). Using three established serological assays, a lower proportion of children seroconverted compared with adults [20/54 (37.0%) vs 32/42 (76.2%); (p<0.001)]. This was not related to viral load, which was similar in children and adults [mean Ct 28.58 (SD: 6.83) vs 24.14 (SD: 8.47)]. Age and sex also did not influence seroconversion or the magnitude of antibody response within children or adults. Notably, in adults (but not children) symptomatic adults had three-fold higher antibody levels than asymptomatic adults (median 227.5 IU/mL, IQR 133.7-521.6 vs median 75.3 IU/mL, IQR 36.9-113.6). Evidence of cellular immunity was observed in adults who seroconverted but not in children who seroconverted. Conclusion and Relevance In this non-hospitalized cohort with mild COVID-19, children were less likely to seroconvert than adults despite similar viral loads. This has implications for future protection following COVID-19 infection in children and for interpretation of serosurveys that involve children. Further research to understand why children are less likely to seroconvert and develop symptoms following SARS-CoV-2 infection, and comparison with vaccine responses may be of clinical and scientific importance. Key points Question What proportion of children with non-hospitalized (mild) SARS-CoV-2 infection seroconvert compared to adults? Findings In this cohort study conducted in 2020, we found the proportion of children who seroconverted to SARS-CoV-2 was half that in adults despite similar viral load. Meaning Serology is a less reliable marker of prior SARS-CoV-2 infection in children. SARS-CoV-2-infected children who do not seroconvert may be susceptible to reinfection. Our findings support strategies to protect children against COVID-19 including vaccination.

Immune Responses in an Infant with Congenital Heart Disease and Severe COVID-19 (preprint)

Children have lower hospitalisation and mortality rates for coronavirus disease-2019 (COVID-19) than adults; however, younger children (<4 years of age)1 may develop more severe disease than older children. To date, the immune correlates of severe COVID-19 in young children have been poorly characterized. We report the kinetics of immune responses in relation to clinical and virological features in an infant with acute severe COVID-19. Systemic cellular and cytokine profiling showed initial increase in neutrophils and monocytes with depletion of lymphoid cell populations (particularly CD8+ T and NK cells) and elevated inflammatory cytokines. Expansion of memory CD4+T (but not CD8+T) cells occurred over time, with predominant Th2 bias. Marked activation of T cell populations observed during the acute infection gradually resolved as the child recovered. Significant in vitro activation of T-cell populations and robust cytokine production, in response to inactivated SARS-CoV-2 stimulation, was observed 3 months after infection indicating durable, long-lived cellular immune memory.

Immune responses to SARS-CoV-2 in children of parents with symptomatic COVID-19 (preprint)

Compared to adults, children with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have mild or asymptomatic infection, but the underlying immunological differences remain unclear. We describe clinical features, virology, longitudinal cellular and cytokine immune profile, SARS-CoV-2-specific serology and salivary antibody responses in a family of two parents with PCR-confirmed symptomatic SARS-CoV-2 infection and their three children, who were repeatedly SARS-CoV-2 PCR negative. Cellular immune profiles and cytokine responses of all children were similar to their parents at all timepoints. All family members had salivary anti-SARS-CoV-2 antibodies detected, predominantly IgA, that coincided with symptom resolution in 3 of 4 symptomatic members. Plasma from both parents and one child had IgG antibody detected against the S1 protein and virus neutralising activity ranging from just detectable to robust titers. Using a systems serology approach, we show that all family members demonstrated higher levels of SARS-CoV-2-specific antibody features than healthy controls. These data indicate that children can mount an immune response to SARS-CoV-2 without virological evidence of infection. This raises the possibility that despite chronic exposure, immunity in children prevents establishment of SARS-CoV-2 infection. Relying on routine virological and serological testing may therefore not identify exposed children, with implications for epidemiological and clinical studies across the life-span.