Effectiveness of the CoronaVac® vaccine in a region of the Colombian Amazon, was herd immunity achieved?

Enhancing Immunological Memory: Unveiling Booster Doses to Bolster Vaccine Efficacy Against Evolving SARS-CoV-2 Mutant Variants

A growing number of re-infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in previously immunized individuals has sparked discussions about the potential need for a booster vaccine dosage to counteract declining antibody levels and new strains. The protective immunity produced by vaccinations, and past illnesses relies on immunological memory. CD4 + T cells, CD8 + T cells, B cells, and long-lasting antibody responses are all components of the adaptive immune system that can generate and maintain this immunological memory. Since novel mutant variants have emerged one after the other, the world has been hit by repeated waves. Various vaccine formulations against SARS-CoV-2 have been administered across the globe. Thus, estimating the efficacy of those vaccines against gradually developed mutant stains is the essential parameter regarding the fate of those vaccine formulations and the necessity of booster doses and their frequency. In this review, focus has also been given to how vaccination stacks up against moderate and severe acute infections in terms of the longevity of the immune cells, neutralizing antibody responses, etc. However, hybrid immunity shows a greater accuracy of re-infection of variants of concern (VOCs) of SARS-CoV-2 than infection and immunization. The review conveys knowledge of detailed information about several marketed vaccines and the status of their efficacy against specific mutant strains of SARS-CoV-2. Furthermore, this review discusses the status of immunological memory after infection, mixed infection, and vaccination.

Comparison of antibody responses following natural infection with Severe Acute Respiratory Syndrome Coronavirus 2 or receipt of CoronaVac or ChAdOx1 (AZD1222) vaccination in Chiang Mai, Thailand

Background

In Thailand, early vaccination initiatives for SARS-CoV-2 relied on CoronaVac (Sinovac Life Sciences) and ChAdOx1 (Oxford-AstraZeneca) vaccines. However, the data of immunogenicity of these two vaccines in Thai populations is limited. This real time, head-to-head comparative study was conducted to investigate antibody (Ab) responses to SARS-CoV-2 following infection or receipt of either CoronaVac or ChAdOx1 vaccination in Chiang Mai, Thailand.

Methods

Sera was collected within two months from participants having a history of documented SARS-CoV-2 infection or at one month after the second dose of CoronaVac vaccine. Sera from participants with a history of receiving one dose of ChAdOx1 vaccination was collected twice, at one month following each vaccine dose. Neutralizing antibodies (NAbs) were assessed using the surrogate neutralization test and anti-spike protein antibodies were assessed using an in-house enzyme-linked immunosorbent assay.

Results

The prevalence of NAbs against SARS-CoV-2 was 92.1 %, 95.7 %, 64.1 % and 100 % in the infection group, CoronaVac group, ChAdOx1 group after 1st dose, and ChAdOx1 group after 2nd dose, respectively. The inhibition rate in individuals receiving two doses of ChAdOx1 vaccine (90.8%) was significantly higher than individuals who had recovered from natural infection (71.7%) or individuals who had received two doses of CoronaVac vaccine (66.7%). The prevalence of anti-spike Abs was 97.4 %, 97.8 %, 97.4 % and 100 % in the infection group, CoronaVac group, ChAdOx1 group after 1st dose, and ChAdOx1 group after 2nd dose, respectively. Significantly higher levels of anti-spike Abs were observed in the ChAdOx1 group after two doses of vaccination (1975 AU/mL) compared to those who had recovered from natural infection (468.5 AU/mL) and individuals who had received CoronaVac (554.4 AU/mL). Neutralizing activity had a statistically significant positive correlation with levels of anti-spike Abs.

Conclusions

ChAdOx1 vaccine may provide superior immunogenicity than CoronaVac and natural infection.

Genomic epidemiology of SARS-CoV-2 variants during the first two years of the pandemic in Colombia

BACKGROUND

The emergence of highly transmissible SARS-CoV-2 variants has led to surges in cases and the need for global genomic surveillance. While some variants rapidly spread worldwide, other variants only persist nationally. There is a need for more fine-scale analysis to understand transmission dynamics at a country scale. For instance, the Mu variant of interest, also known as lineage B.1.621, was first detected in Colombia and was responsible for a large local wave but only a few sporadic cases elsewhere.

METHODS

To better understand the epidemiology of SARS-Cov-2 variants in Colombia, we used 14,049 complete SARS-CoV-2 genomes from the 32 states of Colombia. We performed Bayesian phylodynamic analyses to estimate the time of variants' introduction, their respective effective reproductive number, and effective population size, and the impact of disease control measures.

RESULTS

Here, we detect a total of 188 SARS-CoV-2 Pango lineages circulating in Colombia since the pandemic's start. We show that the effective reproduction number oscillated drastically throughout the first two years of the pandemic, with Mu showing the highest transmissibility (Re and growth rate estimation).

CONCLUSIONS

Our results reinforce that genomic surveillance programs are essential for countries to make evidence-driven interventions toward the emergence and circulation of novel SARS-CoV-2 variants.

Vaccine coverage and effectiveness against laboratory-confirmed symptomatic and severe Covid-19 in indigenous people in Brazil: a cohort study

BACKGROUND

Indigenous people have historically suffered devastating impacts from epidemics and continue to have lower access to healthcare and be especially vulnerable to respiratory infections. We estimated the coverage and effectiveness of Covid-19 vaccines against laboratory-confirmed Covid-19 cases among indigenous people in Brazil.

METHODS

We linked nationwide Covid-19 vaccination data with flu-like surveillance records and studied a cohort of vaccinated indigenous people aged ≥ 5 years between 18th January 2021 and 1st March 2022. We considered individuals unexposed from the date they received the first dose of vaccine until the 13th day of vaccination, partially vaccinated from the 14th day after the first dose until the 13th day after receiving the second dose, and fully vaccinated onwards. We estimated the Covid-19 vaccination coverage and used Poisson regression to calculate the relative risks (RR) and vaccine effectiveness (VE) of CoronaVac, ChAdOx1, and BNT162b2 against Covid-19 laboratory-confirmed cases incidence, mortality, hospitalisation, and hospital-progression to Intensive Care Unit (ICU) or death. VE was estimated as (1-RR)*100, comparing unexposed to partially or fully vaccinated.

RESULTS

By 1st March 2022, 48.7% (35.0-62.3) of eligible indigenous people vs. 74.8% (57.9-91.8) overall Brazilians had been fully vaccinated for Covid-19. Among fully vaccinated indigenous people, we found a lower risk of symptomatic cases (RR: 0.47, 95%CI: 0.40-0.56) and mortality (RR: 0.47, 95%CI: 0.14-1.56) after the 14th day of the second dose. VE for the three Covid-19 vaccines combined was 53% (95%CI:44-60%) for symptomatic cases, 53% (95%CI:-56-86%) for mortality and 41% (95%CI:-35-75%) for hospitalisation. In our sample, we found that vaccination did not reduce Covid-19 related hospitalisation. However, among hospitalised patients, we found a lower risk of progression to ICU (RR: 0.14, 95%CI: 0.02-0.81; VE: 87%, 95%CI:27-98%) and Covid-19 death (RR: 0.04, 95%CI:0.01-0.10; VE: 96%, 95%CI: 90-99%) after the 14th day of the second dose.

CONCLUSIONS

Lower coverage but similar Covid-19 VE among indigenous people than overall Brazilians suggest the need to expand access, timely vaccination, and urgently offer booster doses to achieve a great level of protection among this group.

Effectiveness of BNT162b2 and CoronaVac vaccinations against SARS-CoV-2 omicron infection in people aged 60 years or above: a case-control study

BACKGROUND

In view of limited evidence that specifically addresses vaccine effectiveness (VE) in the older population, this study aims to evaluate the real-world effectiveness of BNT162b2 and CoronaVac in older adults during the Omicron BA.2 outbreak.

METHODS

This case-control study analyzed data available between January and March 2022 from the electronic health databases in Hong Kong and enrolled individuals aged 60 or above. Each case was matched with up to 10 controls by age, sex, index date and Charlson Comorbidity Index for the four outcomes (COVID-19 infection, COVID-19-related hospitalization, severe complications, and all-cause mortality) independently. Conditional logistic regression was conducted to evaluate VE of BNT162b2 and CoronaVac against COVID-19-related outcomes within 28 days after COVID-19 infection among participants stratified by age groups (60-79, ≥80 years old).

RESULTS

A dose-response relationship between the number of vaccine doses received and protection against severe or fatal disease was observed. Highest VE (95% CI) against COVID-19 infection was observed in individuals aged ≥80 who received three doses of BNT162b2 [75.5% (73.1-77.7%)] or three doses of CoronaVac [53.9% (51.0-56.5%)] compared to those in the younger age group who received three doses of BNT162b2 [51.1% (49.9-52.4%)] or three doses of CoronaVac [2.0% (-0.1-4.1%)]. VE (95% CI) was higher for other outcomes, reaching 91.9% (89.4-93.8%) and 86.7% (84.3-88.8%) against COVID-19-related hospitalization; 85.8% (61.2-94.8%) and 89.8% (72.4-96.3%) against COVID-19-related severe complications; and 96.4% (92.9-98.2%) and 95.0% (92.1-96.8%) against COVID-19-related mortality after three doses of BNT162b2 and CoronaVac in older vaccine recipients, respectively. A similar dose-response relationship was established in younger vaccine recipients and after stratification by sex and Charlson Comorbidity Index.

CONCLUSION

Both BNT162b2 and CoronaVac vaccination were effective in protecting older adults against COVID-19 infection and COVID-19-related severe outcomes amidst the Omicron BA.2 pandemic, and VE increased further with the third dose.

CoronaVac: A review of efficacy, safety, and immunogenicity of the inactivated vaccine against SARS-CoV-2

CoronaVac, also known as the Sinovac inactivated SARS-CoV-2 vaccine, has been widely implemented in combating the COVID-19 pandemic. We summarized the results of clinical trials and real-world studies of CoronaVac in this review. The overall efficacy for the prevention of symptomatic COVID-19 (before the emergence of variants of concern) using two doses of 3 μg CoronaVac was 67.7% (95% CI, 35.9% to 83.7%). Effectiveness in preventing hospitalizations, ICU admissions, and deaths was more prominent than that in preventing COVID-19. A third dose inherited the effectiveness against non-variants of concern and increased effectiveness against severe COVID-19 outcomes caused by omicron variants compared to two doses. Most adverse reactions were mild. Few vaccine-related serious adverse reactions have been reported. Moreover, three-dose regimen significantly increased the seroconversion levels of neutralizing antibodies against omicron as compared to two-dose regimen. This review of CoronaVac may provide a scientific basis for optimizing global immunization strategies.

Impact of SARS-CoV-2 Mu variant on vaccine effectiveness: a comparative genomics study at the peak of the third wave in Bogota, Colombia

We assessed the circulation of severe acute respiratory syndrome coronavirus‐2 variants amongst vaccinated military personnel in Bogotá, Colombia to evaluate the mutations of certain variants and their potential for breakthrough infection in vaccinated subjects. We observed that in vaccinated individuals the most frequent infecting lineage was Mu (B.1.621 and B.1.621.1). The above is possibly associated with specific mutations that confer it with vaccine‐induced immune escape ability. Our findings highlight the importance of how genomic tracking coupled with epidemiological surveillance can assist in the study of novel emerging variants (e.g., Omicron) and their impact on vaccination efforts worldwide.