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Introduction COVID-19 vaccines have been highly effective in reducing morbidity and mortality during the pandemic. However, the emergence of the Omicron (B.1.1.529) variant and subvariants as the globally dominant strains have raised doubts about the effectiveness of currently-available vaccines and prompted debate about potential future vaccination strategies. Areas covered Using the publicly available IVAC VIEW-hub platform, we reviewed 52 studies on vaccine effectiveness (VE) after booster vaccinations. VE data were reported for SARS-CoV-2 symptomatic infection, severe disease and death and stratified by vaccine schedule and age. In addition, a non-systematic literature review of safety was performed to identify single or multi-country studies investigating adverse event rates for at least two of the currently-available COVID-19 vaccines. Expert opinion Booster shots of the current COVID-19 vaccines provide consistently high protection against Omicron-related severe disease and death. Additionally, this protection appears to be conserved for at least 3 months, with a small but significant waning after that time. The positive risk-benefit ratio of these vaccines is well established, thus increasing confidence in administering additional doses as required. Future vaccination strategies will likely include a combination of schedules based on a person’s risk profile, as overly frequent boosting may be neither beneficial nor sustainable for the general population.

IntroductionCOVID-19 vaccines have been highly effective in reducing morbidity and mortality during the pandemic. While primary series vaccination rates are generally high in Southeast Asian (SEA) countries, various factors have limited the rollout and impact of booster doses.Areas coveredWe reviewed 79 studies in the publicly available International Vaccine Access Center (IVAC) VIEW-hub platform on vaccine effectiveness (VE) after primary immunizations with two-dose schedules. VE data were reported for SARS-CoV-2 infection, COVID-19-related hospitalizations and deaths, and stratified across variants of concern (VOC), age, study design and prior SARS-CoV-2 infection for mRNA vaccines (BNT162b2, mRNA-1273 and combinations of both), vector vaccines (AstraZeneca, AZD1222 “Vaxzevria”) and inactivated virus vaccines (CoronaVac).Expert opinionThe most-studied COVID-19 vaccines provide consistently high (>90%) protection against serious clinical outcomes like hospitalizations and deaths, regardless of variant. Additionally, this protection appears equivalent for mRNA vaccines and vector vaccines like AZD1222, as supported by our analysis of local Asian and relevant international data, and by insights from SEA experts. Given the continued impact of COVID-19 hospitalizations and deaths on healthcare systems worldwide, encouraging vaccination strategies that can reduce this burden is more relevant than attempting to prevent broader but milder infections with specific variants, including Omicron.Article highlights - VE was high and comparable for both AZD1222 and mRNA vaccine types (91%-93%) in protecting against hospitalization and death from COVID-19, regardless of age.- VE against symptomatic infections trended higher (though not significantly) for mRNA-based vaccines compared to AZD1222.- Waning of VE since time of vaccination was observed for symptomatic infections but was limited for serious COVID-19 outcomes. A sub-analysis of studies with comparative arms evaluating the VE of different vaccines in the same settings also confirmed these observations for all VOC assessed, with all vaccines conferring a high level of protection against serious outcomes.- For Omicron, there is limited comparative data within the IVAC dataset, however, expert review of emerging data suggests that VE against all outcomes is lower for all COVID-19 vaccines, than for the Delta variant.- Data from the UK indicate that VE improves with a booster dose and that VE continues to be very similar, irrespective of the type of vaccine used.- Importantly, all COVID-19 vaccines evaluated here have favorable benefit/risk profiles.- Although many SEA countries have high rates of primary vaccination, there are still challenges to achieving high booster dose coverage. The results of this analysis suggest that the most effective way to achieve vaccine booster targets, particularly in resource-limited settings, would simply be to consider any vaccines which have good safety and comparable effectiveness profiles, particularly against severe outcomes, and that are accessible and optimal for the local situation.- This review reinforces the value of real-world evidence to support efforts advocating for the completion of primary series and booster vaccinations where appropriate, especially to restore VE against emerging VOC such as Omicron. However, data gaps still persist, given the lag between the emergence of new variants, updated vaccine schedules and VE data to inform their impact.

Objective: To evaluate the long-term persistence of anti-hepatitis B surface (HBs) antibodies and the response to a HB challenge re-vaccination in children who had received a primary series of DTaP-IPV-HB-PRP∼T (Hexaxim™) or DTaP-IPV-HB/PRP∼T (Infanrix hexa™). Methods: Two cohorts of participants who had previously received HB vaccine at birth followed by either DTaP-IPV-HB-PRP∼T or DTaP-IPV-HB/PRP∼T co-administered with PCV7 at 2, 4, 6 months of age in a randomized, Phase III, observer-blind study in Thailand, were followed up for anti-HBs antibodies (geometric mean concentrations [GMCs] and seroprotection [SP] rate [% of participants with a titer ≥10 mIU/mL]) at 12–18 months of age and 9–10 years of age. A monovalent HB challenge re-vaccination was administered at 9–10 years of age and the anamnestic response was evaluated. Results: Anti-HBs GMCs and SP rates in the DTaP-IPV-HB-PRP∼T and DTaP-IPV-HB/PRP∼T groups were high and similar post-primary vaccination series (2477 mIU/mL and 99.5% and 2442 mIU/mL and 99.5%, respectively) and declined to a similar extent in each group at 12–18 months (154.5 mIU/mL and 90.8% and 162.3 mIU/mL and 96.5%, respectively). Antibody levels further declined at 9–10 years of age (13.3 mIU/mL and 49.3% and 8.0 mIU/mL and 42.9%) and a strong anamnestic response occurred in each group post-HB challenge re-vaccination (92.8% and 98.7%, respectively). Conclusion: The kinetics of long-term anti-HBs antibody persistence were similar following a primary series of DTaP-IPV-HB-PRP∼T or DTaP-IPV-HB/PRP∼T. The response to a subsequent HB challenge re-vaccination was strong and similar in each group, demonstrating persisting immune memory.

The current study examined the safety and immunogenicity of 23-valent pneumococcal capsular polysaccharide vaccine (Pneumo23(®) [PPV23], Sanofi Pasteur) as a booster dose in 12- to 18-month-old children primed with heptavalent pneumococcal vaccine (PCV7; Prevnar(®), Pfizer). This was a randomized, observer-blinded, 2-arm, controlled, multicenter phase III study performed in Thailand to assess and describe the immunogenicity and safety of PPV23 as a booster dose in children who had received the 3 primary doses of PCV7, the pneumococcal vaccine available during the study period. Children primed with 3 doses of PCV7 were randomized 1:1 to receive a booster immunization with PPV23 or PCV7. Pneumococcal antibody concentrations were measured by enzyme-linked immunosorbent assay and functional antibody levels by multiplex opsonophagocytosis assay on day 30. A total of 339 children were enrolled. Geometric mean serum antibody concentrations against serotypes common to PCV7 and PPV23 (4, 6B, 9V, 14, 18C, 19F, and 23F) increased in both groups but they were higher for serotypes 4, 9V, 18C, and 19F in the PPV23 group. Opsonization indices increased in both groups for all measured serotypes (1, 6B, 14, 19A, and 23F) and were higher for serotypes 6B, 14, and 23F in the PCV7 group and for serotypes 1 and 19A in PPV23 group. Solicited reactions and unsolicited adverse events were similar in the 2 groups and generally mild and transient. No treatment-related serious adverse events were reported. These results confirm that boosting with PPV23 is immunogenic and well tolerated in healthy toddlers primed with PCV7.

This single-group study investigated the immunogenicity and safety of a booster dose of the recently licensed live attenuated chimeric Japanese encephalitis vaccine in 50 healthy children (1-5 years old) who were primed with the live attenuated SA14-14-2 vaccine. A strong anamnestic response was induced 28 days postbooster: geometric mean titer, 9144 (95% confidence interval: 7365-11353); and seroprotection rate, 49 of 49 (100%) children.

BackgroundJapanese encephalitis is a mosquito-borne viral disease endemic in most countries in Asia. A recombinant live, attenuated Japanese encephalitis virus vaccine, JE-CV, is licensed in 14 countries, including Thailand, for the prevention of Japanese encephalitis in adults and children.MethodsThis was a prospective, phase IV, open-label, multicentre, safety study of JE-CV conducted from November 2013 to April 2015, to evaluate rare serious adverse events (AEs). JE-CV was administered to 10,000 healthy children aged 9months to

Booster vaccination of infants aims to further reduce the burden of childhood infectious diseases. This study assessed the antibody persistence induced by a primary series vaccination at 2, 4, 6 months of age and a first booster at 18-19 months of age with a pentavalent diphtheria, tetanus, acellular pertussis, inactivated poliovirus, Haemophilus influenzae type b combined vaccine (DTaP-IPV//PRP-T) in 4-6 year-old Thai children (N=123). The safety and immunogenicity of a tetravalent acellular pertussis combined vaccine (containing the same DTaP-IPV antigens as the previous vaccine) given as a second booster at 4 to 6 years of age was also evaluated. Seroprotective antibody levels against diphtheria (or = 0.01 IU/ml), tetanus (or = 0.10 IU/ml), and polioviruses (or = 8 1/dil) were maintained 4-6 years after primary-vaccination and first booster byor = 92.7% of children, and anti-pertussis antibodiesor = 5 EU/ml were observed in the majority of children. The second booster with DTaP-IPV elicited a strong response for all antigens. GMT or GMC ratios for all antigens at the pre- and post-booster samples were from 4.7 to 52.5. Primary vaccination at 2, 4, 6 and a booster at 18-19 months of age with the DTaP-IPV//PRP-T vaccine induced satisfactory antibody persistence at 4-6 years of age. A second booster with DTaP-IPV induced a strong immune response and was well tolerated.

The objective of this study was to evaluate the immunogenicity and safety of a pentavalent vaccine (Pentaxim) containing diphtheria, tetanus, acellular pertussis, inactivated poliovirus, and Hib polysaccharide-conjugate (DTaP-IPV//PRP-T) antigens, in Thai children. One hundred eighty-six infants who had received a hepatitis B vaccine at birth were given a pentavalent vaccine at 2, 4 and 6 months of age and a hepatitis B vaccine concomitantly at 2 and 6 months of age. Immunogenicity was high for each vaccine antigen. The study vaccine was well tolerated and side effects were few. After the third dose, 100% of subjects had an anti-PRPor = 0.15 microg/ml and 96.5%or = 1.0 microg/ml; the anti-PRP GMT was 9.53 microg/ml. Seroprotective rates for diphtheria and tetanus (or = 0.01 IU/ml) were 99.4% and 100%, respectively, and 100% for all three poliovirus types (or = 8 1/dil U). The vaccine response rates to pertussis antigens (a 4-fold increase in antibody titer were 94.1% for PT and 93.0% for FHA. The DTaP-IPV//PRP-T vaccine given at 2, 4 and 6 months of age concomitantly with a monovalent hepatitis B vaccine, was well tolerated and highly immunogenic for primary immunization of infants in Thailand.

This study assessed the booster immune response to a pentavalent combination vaccine containing diphtheria, tetanus, acellular pertussis, inactivated poliovirus, and conjugated-Hib polysaccharide antigens, (DTaP-IPV//PRP-T, Pentaxim, an AcXim family vaccine) at 18-24 months of age. Study subjects received a three-dose primary vaccination at 2, 4 and 6 months with a hexavalent vaccine containing the same antigens plus recombinant hepatitis B surface antigen. Antibody concentrations were measured immediately before and one month after vaccination. Reactogenicity and safety were evaluated from parent reports. Before the booster dose, 92.9% of the 156 children included in this study still had anti-PRP antibody titersor = 0.15 microg/ml. Seroprotective concentrations of anti-diphtheria, tetanus and poliovirus antibodies were maintained in 97 to 100% of subjects in the interval between primary and booster vaccination. One month after the booster dose, all subjects had seroprotective anti-PRP (or = 1 microg/ml), diphtheria and tetanus (or = 0.1 IU/ml) and poliovirus types 1, 2, 3 (or = 8 1/dil) antibody levels. At least 92.3% of subjects had 4-fold increases in concentrations of anti-pertussis antigens from pre- to post-booster dose. Geometric mean titers (GMTs) increased from 3.8 to 181.2 EU/ml and from 18.0 to 289.7 EU/ml for anti-PT and anti-FHA, respectively. The anti-PRP GMT increased from 1.6 to 58.0 microg/ml. The pentavalent DTaP-IPV//PRP-T vaccine booster was well tolerated and highly immunogenic, following primary vaccination with a hexavalent vaccine.

This observational study determined the prevalence of influenza and influenza-like-illness (ILI) in patients hospitalized for acute coronary syndrome (ACS). Serological confirmation and a clinical history of influenza or a recent acute upper respiratory infection were obtained in 376 patients admitted to Maharaj Nakhon Chiang Mai Hospital, Thailand, from June 2006 through May 2007 for ACS. We found evidence of confirmed influenza preceding ACS in 47 patients (12.5%) and for recent ILI in 41 patients (11%). There were more influenza and ILI patients admitted in the winter than in other months. Influenza vaccination may be protective in high risk patients.