Immunological responses and adverse reactions of the heterologous second booster dose of BNT162b2 after two-dose CoronaVac for COVID-19 vaccination in healthcare workers of Faculty of Medicine,Naresuan University

BackgroundThe first COVID-19 vaccination campaign in Thailand began in April 2020, with healthcare workers receiving two doses of inactivated COVID-19 vaccine (CoronaVac). However, the emergence of the delta and omicron variants raised concerns about vaccine effectiveness. The Thai Ministry of Public Health provided the first booster dose (third dose) and second booster dose (fourth dose) of the mRNA vaccine (BNT162b2) for healthcare workers. This study investigated the immunity and adverse reactions elicited by a heterologous second booster dose of BNT162b2 after a two-dose CoronaVac vaccination for COVID-19 in healthcare workers of the Faculty of Medicine, Naresuan University.MethodsIgG titres against the SARS-CoV-2-spike protein were measured four and 24 weeks after the second booster dose of BNT162b2 in the study participants. Adverse reactions were recorded during the first three days, four weeks and 24 weeks after the second booster dose of BNT162b2.ResultsIgG against the SARS-CoV-2-spike protein was positive (>10 U/ml) in 246 of 247 participants (99.6 %) at both four and 24 weeks after the second booster dose of BNT162b2. The median specific IgG titres at four and 24 weeks after the second booster dose of BNT162b2 were 299 U/ml (min: 2, max: 29,161) and 104 U/ml (min: 1, max: 17,920), respectively. The median IgG level declined significantly 24 weeks after the second booster dose of the BNT162b2 vaccine. Of the 247 participants, 179 (72.5 %) experienced adverse reactions in the first three days after the second booster dose of BNT162b2. Myalgia, fever, headache, injection site pain and fatigue were the most common adverse reactions.ConclusionThis study demonstrated that a heterologous second booster dose of BNT162b2 after two doses of CoronaVac induced elevated IgG against the SARS-CoV-2-spike protein and caused minor adverse reactions in healthcare workers of the Faculty of Medicine, Naresuan University.This study was registered as Thailand Clinical Trials No. TCTR20221112001.     

Early effectiveness of BNT162b2 Covid-19 vaccine in preventing SARS-CoV-2 infection in healthcare personnel in six Israeli hospitals (CoVEHPI)

BackgroundMethodologically rigorous studies on Covid-19 vaccine effectiveness (VE) in preventing SARS-CoV-2 infection are critically needed to inform national and global policy on Covid-19 vaccine use. In Israel, healthcare personnel (HCP) were initially prioritized for Covid-19 vaccination, creating an ideal setting to evaluate early real-world VE in a closely monitored population.MethodsWe conducted a prospective study among HCP in 6 hospitals to estimate the effectiveness of the BNT162b2 mRNA Covid-19 vaccine in preventing SARS-CoV-2 infection. Participants filled out weekly symptom questionnaires, provided weekly nasal specimens, and three serology samples – at enrollment, 30 days and 90 days. We estimated VE against PCR-confirmed SARS-CoV-2 infection using the Cox Proportional Hazards model and against a combined PCR/serology endpoint using Fisher’s exact test.ResultsOf the 1567 HCP enrolled between December 27, 2020 and February 15, 2021, 1250 previously uninfected participants were included in the primary analysis; 998 (79.8%) were vaccinated with their first dose prior to or at enrollment, all with Pfizer BNT162b2 mRNA vaccine. There were four PCR-positive events among vaccinated participants, and nine among unvaccinated participants. Adjusted two-dose VE against any PCR-confirmed infection was 94.5% (95% CI: 82.6%-98.2%); adjusted two-dose VE against a combined endpoint of PCR and seroconversion for a 60-day follow-up period was 94.5% (95% CI: 63.0%-99.0%). Five PCR-positive samples from study participants were sequenced; all were alpha variant.ConclusionsOur prospective VE study of HCP in Israel with rigorous weekly surveillance found very high VE for two doses of Pfizer BNT162b2 mRNA vaccine against SARS-CoV-2 infection in recently vaccinated HCP during a period of predominant alpha variant circulation.FundingClalit Health Services.     

One-year dynamics of antibody titers after three doses of SARS-CoV-2 BNT162b2 vaccine

BackgroundA third dose of the BNT162b2 SARS-CoV-2 vaccine leads to a significant increase in antibody levels, however, concerns regarding the long-term persistence of this response exist. We assessed the humoral response for one year following vaccination.MethodsA prospective study among immunocompetent healthcare workers (HCW) who received three doses of BNT162b2. anti-spike antibody titers were measured at six predefined timepoints, from before the second vaccine dose, and up to one year afterwards, which is 4–6 months after the third dose. HCW with a history of SARS-CoV-2 infection were excluded.ResultsSeventy-six HCW had all the six serological measurements. Antibody titers significantly increased shortly following the third vaccine dose, and while declining, remained higher from all previous measurements for up to six months.ConclusionsA third dose of BNT162b2 leads to a profound humoral response, which remains significantly higher than previous measurements, even after 6 months.     

Antibody titers among healthcare workers for coronavirus disease 2019 at 6 months after BNT162b2 vaccination

BackgroundAntibody levels decrease substantially at 6 months after the BNT162b2 vaccine. The factors influencing titer of antibodies against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) among healthcare workers for coronavirus disease 2019 (COVID-19) is unclear.MethodsWe conducted a 6-month longitudinal prospective study in Japanese healthcare workers in a tertiary care hospital for COVID-19. Participants in the study were tested for the presence of anti-spike protein (SP) IgG antibodies before and at 1 and 6 months after the last vaccination dose.ResultsAmong 1076 healthcare workers, 794 received the vaccine, and 469 entered the study. Five were infected with SARS-CoV-2 (none among COVID-19 section workers) by the end of the study and 451 participants were finally analyzed (mean age, 42.5 years; 27.3 % male; 18.8 % COVID-19 section workers). Median SP IgG index values were 0.0, 44.4, and 5.5 before and at 1 and 6 months after the last dose, respectively. Regression analysis revealed a negative correlation of SP IgG antibody levels with age (P < 0.0001), and higher levels in COVID-19 section workers (P = 0.0185) and in females (P = 0.0201).ConclusionIn healthcare workers at a COVID-19 hospital, IgG antibody titer was substantially lower at 6 months after receipt of the last dose of the BNT162b2 vaccine compared with that 1 month after the last dose, but was better preserved among younger participants, COVID-19 section workers and females.     

Neutralizing antibody responses in healthcare personnel after three doses of mRNA BNT162b2 vaccine and association with baseline characteristics and past SARS-CoV-2 infection

AimTo estimate neutralizing antibody (NAb) immunity against SARS-CoV-2 in 739 healthcare personnel (HCP) vaccinated with three doses of BNT162b2 mRNA vaccine.MethodsSerum samples were collected at 3, 6, and 9 months after the second vaccine dose and at 7–55 days after the third dose. Samples were tested for NAbs against SARS-CoV-2 receptor binding domain.ResultsThe mean inhibition rates at 3, 6, and 9 months after the second dose were 86.33%, 73.38%, and 61.18%, and increased to 95.57% after the booster dose. Younger HCP and HCP with past SARS-CoV-2 infection had higher inhibition rates while there was an inverse correlation between NAb levels and comorbidities or tobacco use (p-values < 0.001). Increased NAb titers were also noticed in women (p-value = 0.033), especially at the end of the 9-month study period.ConclusionNAb levels increased considerably after a booster mRNA vaccine dose. Host factors and past SARS-CoV-2 infection influence NAb titers.     

Waning effectiveness of CoronaVac in real life: A retrospective cohort study in health care workers

BackgroundReal-world studies showed varying levels of effectiveness of CoronaVac vaccine against COVID-19 disease. This study aimed to assess the association between the vaccination with CoronaVac and the COVID-19 infections among the health care workers in a university hospital and to determine the vaccine effectiveness against COVID-19 in a period when alpha variant was dominant.MethodsThis retrospective cohort study was conducted in a university hospital in Istanbul, Turkey employs 4067 health care workers. The follow-up period was defined as starting 14 days after receiving the second dose for fully vaccinated group. Health care workers were censored when have a positive PCR test result or at the end of the study. Unvaccinated health care workers were censored if they receive any COVID-19 vaccine doses. The incidence rate ratio and Cox regression were used to estimate the unadjusted and adjusted effectiveness of the vaccine.Findings: Seventy-one percent of the health care workers were fully vaccinated whereas 29% percent did not receive any doses. The incidence rate of SARS-CoV-2 infection was 133.7 vs 70.7 per 100.000 person-days in the unvaccinated and fully vaccinated groups, respectively. The unadjusted effectiveness against COVID-19 infection was 47% (95% CI 31–59%) whereas adjusted effectiveness was 39% (95% CI 20–64%).Interpretation: This real life study conducted in health care workers demonstrated that the effectiveness of two doses of the CoronaVac vaccine (39%) was lower than that determined in clinical trials. Due to reduce in protection over time or against variants, booster doses may be needed.     

Safety and effectiveness of BNT162b2 mRNA Covid-19 vaccine in adolescents

In South Korea, all 12th grade students (highs school seniors) were offered BNT162b2 vaccine starting July 19, 2021; while 10^th–11th grade students were not eligible. We conducted a nationwide retrospective cohort study by to determine the safety and effectiveness of BNT162b2 mRNA Covid-19 vaccine in adolescents against SARS-CoV-2 infection. Among 444,313 persons who received the first dose of vaccine, reporting rate for myocarditis and/or pericarditis was 1.8 per 100,000 (95% C.I. 0.8–3.5) among first-dose recipients and 4.3 per 100,000 (95% C.I. 2.6–6.7) in second-dose recipients. Vaccine effectiveness against symptomatic/asymptomatic SARS-CoV-2 infection 14 days post-first dose vaccination was 91.1% (95% C.I. 89.6–92.5), and 14 days post-second dose was 99.1% (95% C.I. 98.5–99.5). In this retrospective cohort study, BNT162b2 vaccination was safe and was associated with a significantly lower risk of SARS-CoV-2 infection, suggesting that vaccination in adolescent may reduce the burden of Covid-19.     

Vaccine Effectiveness,School Reopening,and Risk of Omicron Infection Among Adolescents Aged 12–17 Years

PurposeThe BNT162b2 (Pfizer-BioNTech) is approved for adolescents aged 12–17 years. We estimated BNT162b2 vaccine effectiveness (VE) and a booster dose effectiveness in adolescents aged 12–17 years and the impact of opening schools and the Omicron variant on risk of SARS-CoV-2 infection in adolescents.MethodsWe used logistic regression with a test-negative design controlling for gender and race to estimate BNT162b2 VE and the effectiveness of a booster dose in adolescents aged 12–17 years. To evaluate the effect of school opening on Omicron transmission, we used Cox proportional hazards regression to compare adolescents to a reference group of adults aged 22–33 or aged 65+ years, investigating whether risk for adolescents increased relative to the reference group after school opened.ResultsWe found that adolescents who received two BNT162b2 doses had significant protection against Omicron infection in the first three months following their second dose (VE = 54.5%, confidence interval [CI]: [17.8%–76.9%], p = .014) but no protection afterwards. Receiving a booster dose was associated with lower risk of infection (odds ratio = 0.48, CI: [0.33–0.69], p < .0001) and restored efficacy to a similar level (VE = 56.3%, CI: [36.5%–70.6%], p < .0001). We observed a statistically significant increase (p = .04) in adolescent infection risk relative to adults in the period of Omicron predominance.DiscussionThe BNT162b2 vaccine is effective at preventing SARS-CoV-2 infection in adolescents but immunity against Omicron wanes rapidly and booster doses are needed to retain protection. More research is needed to determine the effect of school reopening on spread in the Omicron-dominant period.     

BNT162b2 mRNA COVID-19 against symptomatic Omicron infection following a mass vaccination campaign in southern Brazil: A prospective test-negative design study

BackgroundEvidence regarding effectiveness of BNT162b2 mRNA COVID-19 vaccine against Omicron in Latin America is limited. We estimated BNT162b2 effectiveness against symptomatic COVID-19 in Brazil when Omicron was predominant.MethodsThis prospective test-negative, case-control study was conducted in Toledo, Brazil, following a mass COVID-19 vaccination with BNT162b2. Patients were included if they were aged ≥12 years, sought care for acute respiratory symptoms in the public health system between November 3, 2021 and June 20, 2022, and were tested for SARS-CoV-2 using RT-PCR. In the primary analysis, we determined the effectiveness of two doses of BNT162b2 against symptomatic COVID-19.ResultsA total of 4,574 were enrolled; of these, 1,758 patients (586 cases and 1,172 controls) were included in the primary analysis. Mean age was 27.7 years, 53.8 % were women, and 90.1 % had a Charlson comorbidity index of zero. Omicron accounted for >97 % of all identified SARS-CoV-2 variants, with BA.1 and BA.2 accounting for 84.3 % and 12.6 %, respectively. Overall adjusted estimate of two-dose vaccine effectiveness against symptomatic COVID-19 was 46.7 % (95 %CI, 19.9 %–64.6 %) after a median time between the second dose and the beginning of COVID-19 symptoms of 94 days (IQR, 60–139 days). Effectiveness waned from 77.7 % at 7–29 days after receipt of a second dose to <30 % (non-significant) after ≥120 days.ConclusionIn a relatively young and healthy Brazilian population, two doses of BNT162b2 provided protection against symptomatic Omicron infection. However, this protection waned significantly over time, underscoring the need for boosting with variant-adapted vaccines in this population prior to waves of disease activity.Trial registration number: ClinicalTrials.gov number, NCT05052307 (https://clinicaltrials.gov/ct2/show/NCT05052307).     

SARS-CoV-2-antibody response in health care workers after vaccination or natural infection in a longitudinal observational study

BackgroundFollowing a year of development, several vaccines have been approved to contain the global COVID-19 pandemic. Real world comparative data on immune response following vaccination or natural infection are rare.MethodsWe conducted a longitudinal observational study in employees at a secondary care hospital affected by the COVID-19 pandemic. Comparisons were made about the presence of anti-SARS-CoV-2 immunglobulin G (IgG) antibody ratio after natural infection, or vaccination with one or two doses of BioNTech/Pfizer (BNT162b2), or one dose of AstraZenca (Vaxzevria) vaccine.ResultsWe found a 100% humoral response rate in participants after 2 doses of BNT162b2 vaccine. The antibody ratio in participants with one dose BNT162b2 and Vaxzevria did not differ significantly to those with previous PCR-confirmed infection, whereas this was significantly lower in comparison to two doses of BioNTech/Pfizer. We could not identify a correlation with previous comorbidities, obesity or age within this study. Smoking showed a negative effect on the antibody response (p = 0.006)ConclusionOur data provide an overview about humoral immune response after natural SARS-CoV-2 infection or following vaccination, and supports the usage of booster vaccinations, especially in patients after a natural SARS-CoV-2 infection.     

Humoral immune response characterization of heterologous prime-boost vaccination with CoronaVac and BNT162b2

BackgroundVaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has proven to be a successful strategy for prevent severe infections. CoronaVac and BNT162b2 are the most used vaccines worldwide, but their use in heterologous vaccination schedules is still subjected to evaluation.MethodsFifty healthy individuals who received heterologous prime-boost vaccination with CoronaVac and BNT162b2 were enrolled in a post-vaccination serological follow-up longitudinal prospective study. We evaluated specific serum anti-receptor binding domain (RBD) IgG antibody levels, and their capacity to block RBD-ACE2 interaction with a surrogate neutralization assay. In 20 participants, we assessed antibody binding kinetics by surface plasmon resonance, and Fc-mediated functions by ADCC and ADCP reporter assays.ResultsOur baseline seronegative cohort, displayed seroconversion after two doses of CoronaVac and an important decrease in serum anti-RBD IgG antibodies levels 80 days post-second dose. These levels increased significantly early after the third dose with BNT162b2, but 73 days after the booster we found a new fall. Immunoglobulin functionalities showed a similar behavior.ConclusionsThe heterologous prime-boost vaccination with CoronaVac and BNT162b2 generated an impressive increase in serum anti-RBD specific antibody levels followed by a drop. Nevertheless, these titers remained well above those found in individuals only vaccinated with CoronaVac in the same elapsed time. Serum IgG levels showed high correlation with antibody binding analysis, their capacity to block RBD-ACE2 interaction, and Fc-effectors mechanisms. Our work sheds light on the humoral immune response to heterologous vaccination with CoronaVac and BNT162b2, to define a post-vaccination correlate of protection against SARS-CoV-2 infection and to discuss the scheduling of future vaccine boosters in general population.     

Relative effectiveness of COVID-19 vaccination with 3 compared to 2 doses against SARS-CoV-2 B.1.1.529 (Omicron) among an Australian population with low prior rates of SARS-CoV-2 infection

BackgroundWe estimate effectiveness of 3 versus 2 vaccine doses against SARS-CoV-2 B.1.1.529 Omicron in a mostly infection-naiive but highly vaccinated Australian population.MethodsCohort study of adults aged 40+ years resident in Sydney followed from 1 January 2022 for SARS-CoV-2 infection and COVID-19 hospitalisation or death using linked immunisation, disease notification and hospitalisation registers. Adjusted hazard ratios (aHR) and corresponding relative vaccine effectiveness (rVE) were estimated comparing 3 to 2 vaccine dose recipients by time since dose receipt, vaccine brand, and prior infection. Absolute risk reductions and numbers needed to boost by age groups were calculated.Results2,053,123 infection-naiive individuals (mean age 59 years) were followed for 327,272 person-years for infection and 224,269 person-years for severe outcomes (hospitalisation/death). There were 175,849 infections and 4113 hospitalisations/deaths. Compared to individuals receiving dose 2 within the last 3 months, rVE in dose 3 recipients was 7% (95% CI 5–9%) against infection and 65% (95%CI 61–69%) against hospitalisation/death. Almost all dose 3 recipients had an mRNA vaccine; there was little difference in dose 3 rVE by primary course vaccine brand (ChAdOx1 versus BNT162b2). Over the 6-week follow-up, we estimated one hospitalisation/death was avoided for every 192 adults aged ≥70 years boosted with dose 3 in the infection-naiive cohort. The aHR for hospitalisation/death from Omicron was 0.12 (95 %CI 0.07–0.23) for 2-dose recipients with a prior Delta infection compared with 2-dose recipients with no prior infection.ConclusionsReceipt of a third COVID-19 vaccine dose in adults aged 40 years and above significantly reduced hospitalisations and deaths from SARS-CoV-2 Omicron infections in a primarily infection-naiive population.     

Comparative effectiveness of four COVID-19 vaccines,BNT162b2 mRNA,mRNA-1273, ChAdOx1 nCov-19 and NVX-CoV2373 against SARS-CoV-2 B.1.1.529 (Omicron) infection

BackgroundThere is limited data directly comparing the effectiveness of different COVID-19 vaccines.MethodsWe compared rates of SARS-CoV-2 Omicron BA.1/2 infection during March to May 2022 in Australian adults who had received one of four COVID-19 vaccines in the last 14–63 days as either a primary course or a booster dose using Cox proportional hazards models adjusting for age and other characteristics.ResultsAs a primary course, over 2318 person-years and 1033 infections, compared to recipients of BNT162b2 mRNA vaccine, adjusted hazard ratios for SARS-CoV-2 infection were 1.03 (95%CI 0.82–1.30), 1.19 (0.95–1.49), 1.70 (1.46–1.97) for respectively mRNA-1273, ChAdOx-1 nCov-19 and NVX-CoV2373. For the booster dose, over 154,984 person-years and 93,580 infections the respective adjusted hazard ratios compared to BNT162b2 mRNA vaccine were 1.02 (95%CI 1.00–1.04), 1.20 (1.10–1.32), 1.39 (1.20–1.60).ConclusionsOur findings suggest relatively higher effectiveness of ancestral strain mRNA vaccines against SARS-CoV-2 Omicron infection than viral vector and protein subunit vaccines and provide clinical confirmation of immunological data on differences in COVID-19 vaccine performance.     

COVID-19 vaccine perceptions and uptake in a national prospective cohort of essential workers

IntroductionIn a multi-center prospective cohort of essential workers, we assessed knowledge, attitudes, and practices (KAP) by vaccine intention, prior SARS-CoV-2 positivity, and occupation, and their impact on vaccine uptake over time.MethodsInitiated in July 2020, the HEROES-RECOVER cohort provided socio-demographics and COVID-19 vaccination data. Using two follow-up surveys approximately three months apart, COVID-19 vaccine KAP, intention, and receipt was collected; the first survey categorized participants as reluctant, reachable, or endorser.ResultsA total of 4,803 participants were included in the analysis. Most (70%) were vaccine endorsers, 16% were reachable, and 14% were reluctant. By May 2021, 77% had received at least one vaccine dose. KAP responses strongly predicted vaccine uptake, particularly positive attitudes about safety (aOR = 5.46, 95% CI: 1.4–20.8) and effectiveness (aOR = 5.0, 95% CI: 1.3–19.1). Participants’ with prior SARS-CoV-2 infection were 22% less likely to believe the COVID-19 vaccine was effective compared with uninfected participants (aOR 0.78, 95% CI: 0.64–0.96). This was even more pronounced in first responders compared with other occupations, with first responders 42% less likely to believe in COVID-19 vaccine effectiveness (aOR = 0.58, 95% CI 0.40–0.84). Between administrations of the two surveys, 25% of reluctant, 56% reachable, and 83% of endorser groups received the COVID-19 vaccine. The reachable group had large increases in positive responses for questions about vaccine safety (10% of vaccinated, 34% of unvaccinated), and vaccine effectiveness (12% of vaccinated, 27% of unvaccinated).DiscussionOur study demonstrates attitudes associated with COVID-19 vaccine uptake and a positive shift in attitudes over time. First responders, despite potential high exposure to SARS-CoV-2, and participants with a history of SARS-CoV-2 infection were more vaccine reluctant.ConclusionsPerceptions of the COVID-19 vaccine can shift over time. Targeting messages about the vaccine’s safety and effectiveness in reducing SARS-CoV-2 virus infection and illness severity may increase vaccine uptake for reluctant and reachable participants.     

Dynamic of anti-spike receptor binding domain (RBD) levels and short-term adverse events following a heterologous booster dose of BNT162b2 after two doses of CoronaVac in Thai health care workers

BackgroundCoronaVac was administered as the primary COVID-19 vaccine for Thai health care workers (HCWs) in early 2021 in response to the epidemic of new variants. This study aimed to evaluate the dynamic of humoral immune response as well as the short-term side effects resulting from the booster dose of BNT162b2 following completion of a CoronaVac double-dose in Thai HCWs.MethodsThis study was conducted at a teaching hospital in Northern Thailand during August and September 2021. The participants were 50 HCWs who were vaccinated with 2 doses of CoronaVac and were scheduled to receive a booster dose of BNT162b2. Anti-SARS-CoV-2 IgG antibodies levels and short-term side effects were assessed. The anti-RBD level was determined using Architect SARS-CoV-2 IgG II Quant (Abbott).ResultOf the 50 participants, 37 were female. The median age was 33.0 years old. The average time between the second CoronaVac shot and the BNT162b2 booster shot was 81.7 days (SD = 25.0). The median anti-SARS-CoV-2 IgG antibody level on booster vaccination date, as well as day 14, and day 28 after the booster were 335.5 AU/ml, 31,613.5 AU/ml, and 20,311.9 AU/ml, respectively. Fourteen days after the booster, 94% of participants had anti-SARS-CoV-2 IgG antibody levels higher than 50.0 AU/ml. Being female, higher log anti-SARS-CoV-2 IgG antibodies prior to booster vaccination, and longer interval between the second shot and the booster shot were found to be significantly associated with higher levels of anti-SARS-CoV-2 IgG antibodies at both day 14 and day 28 after the booster. There were no reports of serious adverse events.ConclusionA booster dose of BNT162B2 promoted a high level of anti-SARS-CoV-2 IgG antibodies among HCWs who received 2 doses of CoronaVac. The time between the second CoronaVac shot and the booster shot should be at least three months. There were no severe adverse effects observed.     

Effectiveness of Covid-19 vaccines against symptomatic and asymptomatic SARS-CoV-2 infections in an urgent care setting

BackgroundIt is critical to monitor changes in vaccine effectiveness against COVID-19 outcomes for various vaccine products in different population subgroups.MethodsWe conducted a retrospective study in patients ≥12 years who underwent testing for SARS-CoV-2 virus from April 14 through October 25, 2021, at urgent care centers in the New York metropolitan area. Patients self-reported vaccination status at the time of testing. We used a test-negative design to estimate vaccine effectiveness (VE) by comparing odds of a positive test for SARS-CoV-2 infection among vaccinated (n = 474,805), partially vaccinated (n = 87,834), and unvaccinated (n = 369,333) patients, adjusted for demographic factors and calendar time.ResultsVE against symptomatic infection after 2 doses of mRNA vaccine was 96% (95% Confidence Interval: 95%, 97%) in the pre-delta period and reduced to 79% (95% CI: 77%, 81%) in the delta period. In the delta period, VE for 12–15-year-olds (85%; [95% CI: 81%, 88%]) was higher compared to older age groups (<65% for all other age groups). VE estimates did not differ by sex and race/ethnicity. VE against symptomatic infection was the highest for individuals with a prior infection followed by full vaccination. VE against symptomatic infection after the 2-dose mRNA-1273 vaccine (82% [95% CI: 80%, 84%]) was higher compared to the BNT162b2 vaccine (76% [95% CI: 74%, 78%]) in the delta period. VE after 1-dose of the Ad26.COV2.S vaccine was the lowest compared to other vaccines (19% [95% CI: 15%, 23%]) in the delta period.ConclusionsVE against infection after two doses of the mRNA vaccines was high initially, but significantly reduced against the delta variant for both FDA-approved vaccines.     

Antibody response to second dose of the BNT162b2 mRNA vaccine in the first 12 weeks in South Korea: A prospective longitudinal study

ObjectivesTo characterise the antibody response for 12 weeks following second dose of the Pfizer/BioNTech BNT162b2 mRNA vaccine in hospital workers of a Korean general hospital.MethodsWe measured the level of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) anti-receptor binding domain (anti-RBD) and neutralising antibodies every week in the first 4 weeks, and at weeks 8 and 12 following the second dose of vaccination in 71 hospital workers.ResultsThe initial median level of anti-RBD and neutralising antibodies were 3898.0 U/mL (interquartile range [IQR], 2107.5–5478.5) and 97.54 % (IQR, 96.85–97.81), respectively. The levels declined the fastest and the most significantly between weeks 1 and 2 (p < 0.01, both), and continuously decreased thereafter, and were 1163.0 U/mL (683.4–1743.0) and 94.87% (89.24–96.99) at weeks 12. The antibodies levels showed a trend of rapid decrease in the older group over time. The slope of the decrease in the antibodies level was observed for each individual. Within 8 weeks, the anti-RBD antibody levels decreased to less than half of the initial levels in most of the participants (88.7%: 63/71). The SARS-CoV-2 anti-RBD and neutralising antibodies levels showed a strong positive correlation (Spearman’s coefficient = 0.7833).ConclusionsConsiderably high levels of SARS-CoV-2 anti-RBD and neutralising antibodies were produced following the second dose of vaccination. The levels decreased continuously, showing a tendency to decline over time; however, reasonable levels persisted up to weeks 12. Moreover, considering individual variations in antibody response following vaccination, a further inter-individual analysis is needed.     

Dynamics of antibody titers and cellular immunity among Japanese healthcare workers during the 6 months after receiving two doses of BNT162b2 mRNA vaccine

BackgroundThe antibody titer is known to wane within months after receiving two doses of the Pfizer-BioNTech BNT162b2 mRNA SARS-CoV-2 vaccine. However, knowledge of the cellular immune response dynamics following vaccination is limited. This study to aimed to determine antibody and cellular immune responses following vaccination, and the incidence and determinants of breakthrough infection.MethodsThis prospective cohort study a 6-month follow-up period was conducted among Japanese healthcare workers. All participants received two doses of BNT162b2 vaccine. Anti-SARS-CoV-2 antibody titers and T-cell immune responses were measured in serum samples collected at several timepoints before and after vaccination.ResultsA total of 608 participants were included in the analysis. Antibody titers were elevated 3 weeks after vaccination and waned over the remainder of the study period. T-cell immune responses showed similar dynamics. Six participants without predisposing medical conditions seroconverted from negative to positive on the IgG assay for nucleocapsid proteins, indicating breakthrough SARS-CoV-2 infection. Five of the six breakthrough infections were asymptomatic.ConclusionsBoth humoral and cellular immunity waned within 6 months after BNT162b2 vaccination. The incidence of asymptomatic breakthrough infection within 6 months after vaccination was approximately one percent.UMIN Clinical Trials Registry IDUMIN000043340.