RESUMEN
BACKGROUNDThe SARS-CoV-2 Omicron (B.1.1.529) variant has two main sub-lineages, BA.1 and BA.2 with significant genetic distance between them. This study investigated protection of infection with one sub-lineage against reinfection with the other sub-lineage in Qatar during a large BA.1 and BA.2 Omicron wave, from December 19, 2021 to February 21, 2022. METHODSTwo national matched, retrospective cohort studies were conducted to estimate effectiveness of BA.1 infection against reinfection with BA.2 (N=20,197; BA.1-against-BA.2 study), and effectiveness of BA.2 infection against reinfection with BA.1 (N=100,925; BA.2-against-BA.1 study). Associations were estimated using Cox proportional-hazards regression models. RESULTSIn the BA.1-against-BA.2 study, cumulative incidence of infection was estimated at 0.03% (95% CI: 0.01-0.07%) for the BA.1-infected cohort and at 0.62% (95% CI: 0.51-0.75%) for the uninfected-control cohort, 15 days after the start of follow-up. Effectiveness of BA.1 infection against reinfection with BA.2 was estimated at 94.9% (95% CI: 88.4-97.8%). In the BA.2-against-BA.1 study, cumulative incidence of infection was estimated at 0.03% (95% CI: 0.02-0.04%) for the BA.2-infected cohort and at 0.17% (95% CI: 0.15-0.21%) for the uninfected-control cohort, 15 days after the start of follow-up. Effectiveness of BA.2 infection against reinfection with BA.1 was estimated at 85.6% (95% CI: 77.4-90.9%). CONCLUSIONSInfection with an Omicron sub-lineage appears to induce strong, but not full protection against reinfection with the other sub-lineage, for at least several weeks after the initial infection.
RESUMEN
BACKGROUNDQatar has been experiencing a large SARS-CoV-2 Omicron (B.1.1.529) wave that started on December 19, 2021. We assessed duration of protection of BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) COVID-19 vaccines after second dose and after third/booster dose against symptomatic Omicron infection and against COVID-19 hospitalization and death, between December 23, 2021 and February 2, 2022. METHODSVaccine effectiveness was estimated using the test-negative, case-control study design, applying the same methodology used earlier to assess waning of BNT162b2 and mRNA-1273 effectiveness in the same population during earlier infection waves. RESULTSBNT162b2 effectiveness against symptomatic Omicron infection was highest at 61.9% (95% CI: 49.9-71.1%) in the first month after the second dose, but then gradually declined and was at 10% or less starting from the 5th month after the second dose. After the booster, effectiveness rapidly rebounded to peak at about 55% between 2-5 weeks after the booster, but then started to decline again thereafter. Effectiveness against severe, critical, or fatal COVID-19 was maintained at >70% after the second dose and at >90% after the booster with no evidence for declining effectiveness over time. mRNA-1273 effectiveness against symptomatic Omicron infection was highest at 44.8% (95% CI: 16.0-63.8%) in the first three months after the second dose, before gradually declining to negligible levels thereafter. After the booster, effectiveness rapidly rebounded to peak at about 55% between 2-5 weeks after the booster, but then declined again thereafter. Effectiveness against severe, critical, or fatal COVID-19 was high at >60% after the second dose and at >80% after the booster, but the confidence intervals were wide owing to the small number of cases. CONCLUSIONSBNT162b2 and mRNA-1273 vaccines show a similar level and pattern of protection against symptomatic Omicron infection. Protection against Omicron is lower than that against Alpha, Beta, and Delta variants, and wanes more rapidly than against earlier variants after the second and booster doses. Meanwhile, protection against hospitalization and death appears robust and durable after both the second and booster doses.
RESUMEN
BACKGROUNDWaning of COVID-19 vaccine protection and emergence of SARS-CoV-2 Omicron (B.1.1.529) variant have expedited efforts to scale up booster vaccination. This study compared protection afforded by booster doses of the BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) vaccines, compared to the primary series of only two doses in Qatar, during a large, rapidly growing Omicron wave. METHODSIn a population of 2,232,224 vaccinated persons with at least two doses, two matched, retrospective cohort studies were implemented to investigate effectiveness of booster vaccination against symptomatic SARS-CoV-2 infection and against COVID-19 hospitalization and death, up to January 9, 2022. Association of booster status with infection was estimated using Cox proportional-hazards regression models. RESULTSFor BNT162b2, cumulative symptomatic infection incidence was 2.9% (95% CI: 2.8-3.1%) in the booster-dose cohort and 5.5% (95% CI: 5.3-5.7%) in the primary-series cohort, after 49 days of follow-up. Adjusted hazard ratio for symptomatic infection was 0.50 (95% CI: 0.47-0.53). Booster effectiveness relative to primary series was 50.1% (95% CI: 47.3-52.8%). For mRNA-1273, cumulative symptomatic infection incidence was 1.9% (95% CI: 1.7-2.2%) in the booster-dose cohort and 3.5% (95% CI: 3.2-3.9%) in the primary-series cohort, after 35 days of follow-up. The adjusted hazard ratio for symptomatic infection was 0.49 (95% CI: 0.43-0.57). Booster effectiveness relative to primary series was 50.8% (95% CI: 43.4-57.3%). There were fewer cases of severe COVID-19 in booster-dose cohorts than in primary-series cohorts, but cases of severe COVID-19 were rare in all cohorts. CONCLUSIONSmRNA booster vaccination is associated with modest effectiveness against symptomatic infection with Omicron. The development of a new generation of vaccines targeting a broad range of variants may be warranted.
RESUMEN
BACKGROUNDNatural SARS-CoV-2 infection elicits strong protection against reinfection with the Alpha (B.1.1.7), Beta (B.1.351), and Delta (B.1.617.2) variants. However, the Omicron (B.1.1.529) variant harbors multiple mutations that can mediate immune evasion. We estimated effectiveness of prior infection in preventing reinfection (PES) with Omicron and other SARS-CoV-2 variants in Qatar. METHODSPES was estimated using the test-negative, case-control study design, employing a methodology that was recently investigated and validated for derivation of robust estimates for PES. Cases (PCR-positive persons with a variant infection) and controls (PCR-negative persons) were exact-matched by sex, 10-year age group, nationality, and calendar time of PCR test, to control for known differences in the risk of exposure to SARS-CoV-2 infection in Qatar. RESULTSPES against symptomatic reinfection was estimated at 90.2% (95% CI: 60.2-97.6) for Alpha, 84.8% (95% CI: 74.5-91.0) for Beta, 92.0% (95% CI: 87.9-94.7) for Delta, and 56.0% (95% CI: 50.6-60.9) for Omicron. Only 1 Alpha, 2 Beta, 0 Delta, and 2 Omicron reinfections progressed to severe COVID-19. None progressed to critical or fatal COVID-19. PES against hospitalization or death due to reinfection was estimated at 69.4% (95% CI: -143.6-96.2) for Alpha, 88.0% (95% CI: 50.7-97.1) for Beta, 100% (95% CI: 43.3-99.8) for Delta, and 87.8% (95% CI: 47.5-97.1) for Omicron. CONCLUSIONSProtection afforded by prior infection in preventing symptomatic reinfection with Alpha, Beta, or Delta is robust, at about 90%. While such protection against reinfection with Omicron is lower, it is still considerable at nearly 60%. Prior-infection protection against hospitalization or death at reinfection appears robust, regardless of variant.
RESUMEN
BackgroundThe Coronavirus Disease 2019 (COVID-19) pandemic has highlighted an urgent need to use infection testing databases to rapidly estimate effectiveness of prior infection in preventing reinfection (PES) by novel variants of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). MethodsMathematical modeling was used to demonstrate the applicability of the test-negative, case-control study design to derive PES. Modeling was also used to investigate effects of bias in PES estimation. The test-negative design was applied to national-level testing data in Qatar to estimate PES for SARS-CoV-2 infection and to validate this design. ResultsApart from the very early phase of an epidemic, the difference between the test-negative estimate for PES and the true value of PES was minimal and became negligible as the epidemic progressed. The test-negative design provided robust estimation of PES even when PES began to wane after prior infection. Assuming that only 25% of prior infections are documented, misclassification of prior infection status underestimated PES, but the underestimate was considerable only when >50% of the population was ever infected. Misclassification of latent infection, misclassification of current active infection, and scale-up of vaccination all resulted in negligible bias in estimated PES. PES against SARS-CoV-2 Alpha and Beta variants was estimated at 97.0% (95% CI: 93.6-98.6) and 85.5% (95% CI: 82.4-88.1), respectively. These estimates were validated using a cohort study design. ConclusionsThe test-negative design offers a feasible, robust method to estimate protection from prior infection in preventing reinfection.
RESUMEN
BACKGROUNDIn early 2021, Qatar launched a mass immunization campaign with Modernas mRNA-1273 COVID-19 vaccine. We assessed persistence of real-world mRNA-1273 effectiveness against SARS-CoV-2 infection and against COVID-19 hospitalization and death. METHODSEffectiveness was estimated using test-negative, case-control study design, between January 1 and December 5, 2021. Effectiveness was estimated against documented infection (a PCR-positive swab, regardless symptoms), and against any severe (acute-care hospitalization), critical (ICU hospitalization), or fatal COVID-19. RESULTSBy December 5, 2021, 2,962 breakthrough infections had been recorded among those who received two mRNA-1273 doses. Of these infections, 19 progressed to severe COVID-19 and 4 to critical, but none to fatal disease. mRNA-1273 effectiveness against infection was negligible for the first two weeks after the first dose, increased to 65.5% (95% CI: 62.7-68.0%) 14 or more days after the first dose, and reached its peak at about 90% in the first three months after the second dose. Effectiveness declined gradually starting from the fourth month after the second dose and was below 50% by the 7th month after the second dose. Effectiveness against severe, critical, or fatal COVID-19 reached its peak at essentially 100% right after the second dose, and there was no evidence for declining effectiveness over time. Effectiveness against symptomatic versus asymptomatic infection demonstrated the same pattern of waning, but effectiveness against symptomatic infection was consistently higher than that against asymptomatic infection and waned more slowly. CONCLUSIONSmRNA-1273-induced protection against infection appears to wane month by month after the second dose. Meanwhile, protection against hospitalization and death appears robust with no evidence for waning for several months after the second dose.
RESUMEN
BACKGROUNDGrowing evidence suggests that COVID-19 vaccines differ in effectiveness against breakthrough infection or severe COVID-19, but vaccines have yet to be investigated in controlled studies that head-to-head compare immunity of one to another. This study compared protection offered by the mRNA-1273 (Moderna) vaccine with that of the BNT162b2 (Pfizer-BioNTech) vaccine in Qatar. METHODSIn a population of 1,531,736 vaccinated persons, two matched retrospective cohort studies were designed and used to investigate differences in mRNA-1273 and BNT162b2 vaccine protection, after the first and second doses, from December 21, 2020 to October 20, 2021. RESULTSAfter dose 1, cumulative incidence of breakthrough infection was 0.79% (95% CI: 0.75-0.83%) for mRNA-1273-vaccinated individuals and 0.86% (95% CI: 0.82-0.90%) for BNT162b2-vaccinated individuals, 21 days post-injection. Adjusted hazard ratio (AHR) for breakthrough infection was 0.89 (95% CI: 0.83-0.95; p=0.001). AHR was constant in the first two weeks at 1, but it declined to 0.67 (95% CI: 0.57-0.77; p<0.001) in the third week after dose 1. AHR for any severe, critical, or fatal COVID-19 was 0.71 (95% CI: 0.53-0.95; p=0.020). After dose 2, cumulative incidence was 0.59% (95% CI: 0.55-0.64%) for mRNA-1273-vaccinated individuals and 0.84% (95% CI: 0.79-0.89%) for BNT162b2-vaccinated individuals, 180 days post-injection. AHR for breakthrough infection was 0.69 (95% CI: 0.63-0.75; p<0.001) and was largely constant over time after dose 2. AHR for any severe, critical, or fatal COVID-19 was 0.37 (95% CI: 0.10-1.41; p=0.147). CONCLUSIONSmRNA-1273 vaccination is associated with lower SARS-CoV-2 breakthrough infection and COVID-19 hospitalization and death than BNT162b2 vaccination, but the number of hospitalizations and deaths was exceedingly small for both vaccines. Both vaccines demonstrated strikingly similar patterns of build-up of protection after the first dose and waning of protection after the second dose.
RESUMEN
BackgroundThe effective reproduction number, Rt, is a tool to track and understand epidemic dynamics. This investigation of Rt estimations was conducted to guide the national COVID-19 response in Qatar, from the onset of the epidemic until August 18, 2021. MethodsReal-time "empirical" [Formula] was estimated using five methods, including the Robert Koch Institute, Cislaghi, Systrom-Bettencourt and Ribeiro, Wallinga and Teunis, and Cori et al. methods. R was also estimated using a transmission dynamics model [Formula]. Uncertainty and sensitivity analyses were conducted. Agreements between different Rt estimates were assessed by calculating correlation coefficients. Results[Formula] captured the evolution of the epidemic through three waves, public health response landmarks, effects of major social events, transient fluctuations coinciding with significant clusters of infection, and introduction and expansion of the B.1.1.7 variant. The various estimation methods produced consistent and overall comparable [Formula] estimates with generally large correlation coefficients. The Wallinga and Teunis method was the fastest at detecting changes in epidemic dynamics. [Formula] estimates were consistent whether using time series of symptomatic PCR-confirmed cases, all PCR-confirmed cases, acute-care hospital admissions, or ICU-care hospital admissions, to proxy trends in true infection incidence. [Formula] correlated strongly with [Formula] and provided an average [Formula]. ConclusionsRt estimations were robust and generated consistent results regardless of the data source or the method of estimation. Findings affirmed an influential role for Rt estimations in guiding national responses to the COVID-19 pandemic, even in resource-limited settings.
RESUMEN
BACKGROUNDWaning of vaccine protection against SARS-CoV-2 infection or COVID-19 disease is a concern. This study investigated persistence of BNT162b2 (Pfizer-BioNTech) vaccine effectiveness against infection and disease in Qatar, where the Beta and Delta variants have dominated incidence and PCR testing is done at a mass scale. METHODSA matched test-negative, case-control study design was used to estimate vaccine effectiveness against SARS-CoV-2 infection and against any severe, critical, or fatal COVID-19 disease, between January 1, 2021 to August 15, 2021. RESULTSEstimated BNT162b2 effectiveness against any infection, asymptomatic or symptomatic, was negligible for the first two weeks after the first dose, increased to 36.5% (95% CI: 33.1-39.8) in the third week after the first dose, and reached its peak at 72.1% (95% CI: 70.9-73.2) in the first five weeks after the second dose. Effectiveness declined gradually thereafter, with the decline accelerating [≥]15 weeks after the second dose, reaching diminished levels of protection by the 20th week. Effectiveness against symptomatic infection was higher than against asymptomatic infection, but still waned in the same fashion. Effectiveness against any severe, critical, or fatal disease increased rapidly to 67.7% (95% CI: 59.1-74.7) by the third week after the first dose, and reached 95.4% (95% CI: 93.4-96.9) in the first five weeks after the second dose, where it persisted at about this level for six months. CONCLUSIONSBNT162b2-induced protection against infection appears to wane rapidly after its peak right after the second dose, but it persists at a robust level against hospitalization and death for at least six months following the second dose.
RESUMEN
The SARS-CoV-2 Delta (B.1.617.2) variant of concern is expanding globally. Here, we assess real-world effectiveness of the BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) vaccines against this variant in the population of Qatar, using a matched test-negative, case- control study design. BNT162b2 effectiveness against any Delta infection, symptomatic or asymptomatic, was 64.2% (95% CI: 38.1-80.1%) [≥]14 days after the first dose and before the second dose, but was only 53.5% (95% CI: 43.9-61.4%) [≥]14 days after the second dose, in a population in which a large proportion of fully vaccinated persons received their second dose several months earlier. Corresponding effectiveness measures for mRNA-1273 were 79.0% (95% CI: 58.9-90.1%) and 84.8% (95% CI: 75.9-90.8%), respectively. Effectiveness against any severe, critical, or fatal COVID-19 disease due to Delta was 89.7% (95% CI: 61.0-98.1%) for BNT162b2 and 100.0% (95% CI: 41.2-100.0%) for mRNA-1273, [≥]14 days after the second dose. Both BNT162b2 and mRNA-1273 are highly effective in preventing Delta hospitalization and death, but less so in preventing infection, particularly for BNT162b2.
RESUMEN
COVID-19 vaccine protection against infection in immunosuppressed solid organ transplant recipients is unknown but possibly weak with the low proportion of these patients mounting a robust humoral and cellular immune response after vaccination. Using a retrospective cohort study design with cross-over, we assessed vaccine effectiveness among 782 kidney transplant recipients registered at Hamad Medical Corporation, the national public healthcare provider in Qatar, where the BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) vaccines have been used in the national immunization campaign. Vaccine effectiveness against any SARS-CoV-2 infection was estimated at 46.6% (95% CI: 0.0-73.7%) [≥]14 days after the second dose, 66.0% (95% CI: 21.3-85.3%) [≥]42 days after the second dose, and 73.9% (95% CI: 33.0-89.9%) [≥]56 days after the second dose. Vaccine effectiveness against any severe, critical, or fatal COVID-19 disease was estimated at 72.3% (95% CI: 0.0-90.9%) [≥]14 days after the second dose, 85.0% (95% CI: 35.7-96.5%) [≥]42 days after the second dose, and 83.8% (95% CI: 31.3-96.2%) [≥]56 days after the second dose. Most vaccine breakthrough infections occurred in the first few weeks after receiving the first and/or second dose. Vaccine effectiveness reached considerable levels in kidney transplant recipients, but vaccine protection mounted slowly and did not reach a high level until several weeks after the second dose.
RESUMEN
Severity (acute-care hospitalization), criticality (ICU hospitalization), and fatality of SARS-CoV-2 Beta (B.1.351) variant was investigated through case-control studies applied to complete national cohorts of infection, disease, and death cases in Qatar. Compared to Alpha (B.1.1.7) variant, odds of progressing to severe disease were 1.24-fold (95% CI: 1.11-1.39) higher for Beta. Odds of progressing to critical disease were 1.49-fold (95% CI: 1.13-1.97) higher. Odds of COVID-19 death were 1.57-fold (95% CI: 1.03-2.43) higher. Findings highlight risks to healthcare systems, particularly to intensive care facilities and resources, with increased circulation of Beta.
RESUMEN
SARS-CoV-2 breakthrough infections in vaccinated individuals and in those who had a prior infection have been observed globally, but the transmission potential of these infections is unknown. The RT-qPCR cycle threshold (Ct) value is inversely correlated with viral load and culturable virus. Here, we investigated differences in RT-qPCR Ct values across Qatars national cohorts of primary infections, reinfections, BNT162b2 (Pfizer-BioNTech) breakthrough infections, and mRNA-1273 (Moderna) breakthrough infections. Through matched-cohort analyses of the randomly diagnosed infections, the mean Ct value was higher in all cohorts of breakthrough infections compared to the cohort of primary infections in unvaccinated individuals. The Ct value was 1.3 (95% CI: 0.9-1.8) cycles higher for BNT162b2 breakthrough infections, 3.2 (95% CI: 1.8-4.5) cycles higher for mRNA-1273 breakthrough infections, and 4.0 (95% CI: 3.4-4.6) cycles higher for reinfections in unvaccinated individuals. Assuming a linear relationship between viral load and infectiousness, these differences imply that breakthrough infections are at least 50% less infectious than primary infections in unvaccinated individuals. Public health benefits of vaccination may have been underestimated, as COVID-19 vaccines not only protect against acquisition of infection, but also appear to protect against transmission of infection.
RESUMEN
Effect of prior SARS-CoV-2 infection on vaccine protection remains poorly understood. Here, we investigated whether persons vaccinated after a prior infection have better protection against future infection than those vaccinated without prior infection. Effect of prior infection was assessed in Qatars population, where the Alpha (B.1.1.7) and Beta (B.1.351) variants dominate incidence, using two national retrospective, matched-cohort studies, one for the BNT162b2 (Pfizer-BioNTech) vaccine, and one for the mRNA-1273 (Moderna) vaccine. Incidence rates of infection among BNT162b2-vaccinated persons, with and without prior infection, were estimated, respectively, at 1.66 (95% CI: 1.26-2.18) and 11.02 (95% CI: 9.90-12.26) per 10,000 person-weeks. The incidence rate ratio was 0.15 (95% CI: 0.11-0.20). Analogous incidence rates among mRNA-1273-vaccinated persons were estimated at 1.55 (95% CI: 0.86-2.80) and 1.83 (95% CI: 1.07-3.16) per 10,000 person-weeks. The incidence rate ratio was 0.85 (95% CI: 0.34-2.05). Prior infection enhanced protection of those BNT162b2-vaccinated, but not those mRNA-1273-vaccinated. These findings may have implications for dosing, interval between doses, and potential need for booster vaccination.
RESUMEN
We aimed to estimate, albeit crudely and provisionally, national, regional, and global proportions of respective populations that have been infected with SARS-CoV-2, and to assess infection morbidity and mortality rates, factoring both documented and undocumented infections. The estimates were generated by applying mathematical models to 159 countries and territories. The percentage of the worlds population that has been infected as of 31 December 2020 was estimated at 12.56% (95% CI: 11.17-14.05%). It was lowest in the Western Pacific Region at 0.66% (95% CI: 0.59-0.75%) and highest in the Americas at 41.92% (95% CI: 37.95-46.09%). The global infection fatality rate was 10.73 (95% CI: 10.21-11.29) per 10,000 infections. Globally per 1,000 infections, the infection acute-care bed hospitalization rate was 19.22 (95% CI: 18.73-19.51), the infection ICU bed hospitalization rate was 4.14 (95% CI: 4.10-4.18), the infection severity rate was 6.27 (95% CI: 6.18-6.37), and the infection criticality rate was 2.26 (95% CI: 2.24-2.28). If left unchecked with no interventions, the pandemic would eventually cause 8.18 million (95% CI: 7.30-9.18) deaths, 163.67 million (95% CI: 148.12-179.51) acute-care hospitalizations, 33.01 million (95% CI: 30.52-35.70) ICU hospitalizations, 50.23 million (95% CI: 46.24-54.67) severe cases, and 17.62 million (95% CI: 16.36-18.97) critical cases. The global population remains far below the herd immunity threshold and at risk of repeated waves of infection. Global epidemiology reveals immense regional variation in infection exposure and morbidity and mortality rates.
RESUMEN
BackgroundReinfection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been documented, raising public health concerns. Risk and incidence rate of SARS-CoV-2 reinfection were assessed in a large cohort of antibody-positive persons in Qatar. MethodsAll SARS-CoV-2 antibody-positive persons with a PCR-positive swab [≥]14 days after the first-positive antibody test were individually investigated for evidence of reinfection. Viral genome sequencing was conducted for paired viral specimens to confirm reinfection. Incidence of reinfection was compared to incidence of infection in the complement cohort of those antibody-negative. ResultsAmong 43,044 anti-SARS-CoV-2 positive persons who were followed for a median of 16.3 weeks (range: 0-34.6), 314 individuals (0.7%) had at least one PCR positive swab [≥]14 days after the first-positive antibody test. Of these individuals, 129 (41.1%) had supporting epidemiological evidence for reinfection. Reinfection was next investigated using viral genome sequencing. Applying the viral-genome-sequencing confirmation rate, the risk of reinfection was estimated at 0.10% (95% CI: 0.08-0.11%). The incidence rate of reinfection was estimated at 0.66 per 10,000 person-weeks (95% CI: 0.56-0.78). Incidence rate of reinfection versus month of follow-up did not show any evidence of waning of immunity for over seven months of follow-up. Meanwhile, in the complement cohort of 149,923 antibody-negative persons followed for a median of 17.0 weeks (range: 0-45.6), risk of infection was estimated at 2.15% (95% CI: 2.08-2.22%) and incidence rate of infection was estimated at 13.69 per 10,000 person-weeks (95% CI: 13.22-14.14). Efficacy of natural infection against reinfection was estimated at 95.2% (95% CI: 94.1-96.0%). Reinfections were less severe than primary infections. Only one reinfection was severe, two were moderate, and none were critical or fatal. Most reinfections (66.7%) were diagnosed incidentally through random or routine testing, or through contact tracing. ConclusionsReinfection is rare. Natural infection appears to elicit strong protection against reinfection with an efficacy [~]95% for at least seven months.
RESUMEN
BackgroundVaccines against SARS-CoV-2 have been developed, but their availability falls far short of global needs. This study aimed to investigate the impact of prioritizing available doses on the basis of recipient antibody status, that is by exposure status, using Qatar as an example. MethodsVaccination impact was assessed under different scale-up scenarios using a deterministic meta-population mathematical model describing SARS-CoV-2 transmission and disease progression in the presence of vaccination. ResultsFor a vaccine that protects against infection with an efficacy of 95%, half as many vaccinations were needed to avert one infection, disease outcome, or death by prioritizing antibody-negative individuals for vaccination. Prioritization by antibody status reduced incidence at a faster rate and led to faster elimination of infection and return to normalcy. Further prioritization by age group amplified the gains of prioritization by antibody status. Gains from prioritization by antibody status were largest in settings where the proportion of the population already infected at the commencement of vaccination was 30-60%, which is perhaps where most countries will be by the time vaccination programs are up and running. For a vaccine that only protects against disease and not infection, vaccine impact was reduced by half, whether this impact was measured in terms of averted infections or disease outcomes, but the relative gains from using antibody status to prioritize vaccination recipients were similar. ConclusionsMajor health, societal, and economic gains can be achieved more quickly by prioritizing those who are antibody-negative while doses of the vaccine remain in short supply.
RESUMEN
BackgroundThe objective of this study was to forecast the impact of COVID-19 vaccination in the United States (US) and China, two countries at different epidemic phases. MethodsA mathematical model describing SARS-CoV-2 transmission and disease progression was used to investigate vaccine impact. Impact was assessed both for a vaccine that prevents infection (VES = 95%) and a vaccine that prevents only disease (VEP = 95%). ResultsFor VES = 95% and gradual easing of restrictions, vaccination in the US reduced the peak incidence of infection, disease, and death by >55% and cumulative incidence by >32%, and in China by >77% and >65%, respectively. Nearly three vaccinations were needed to avert one infection in the US, but only one was needed in China. For VEP = 95%, benefits of vaccination were half those for VES = 95%. In both countries, the impact of vaccination was substantially enhanced with rapid scale-up, vaccine coverage >50%, and slower or no easing of restrictions, particularly in the US. ConclusionsCOVID-19 vaccination can flatten, delay, and/or prevent future epidemic waves. However, vaccine impact is destined to be heterogeneous across countries because of an underlying "epidemiologic inequity" that reduces benefits for countries already at high incidence, such as the US. Despite 95% efficacy, actual vaccine impact could be meager in such countries, if vaccine scale-up is slow, acceptance of the vaccine is poor, or restrictions are eased prematurely. One Sentence SummaryVaccine impact will be heterogeneous across countries disadvantaging countries at high incidence. This heterogeneity can be alleviated with rapid vaccination scale-up and limited easing of restrictions.
RESUMEN
BackgroundMathematical modeling constitutes an important tool for planning robust responses to epidemics. This study was conducted to guide the Qatari national response to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic. The study investigated the time course of the epidemic, forecasted healthcare needs, predicted the impact of social and physical distancing restrictions, and rationalized and justified easing of restrictions. MethodsAn age-structured deterministic model was constructed to describe SARS-CoV-2 transmission dynamics and disease progression throughout the population. ResultsThe enforced social and physical distancing interventions flattened the epidemic curve, reducing the peaks for incidence, prevalence, acute-care hospitalization, and intensive care unit (ICU) hospitalizations by 87%, 86%, 76%, and 78%, respectively. The daily number of new infections was predicted to peak at 12,750 on May 23, and active-infection prevalence was predicted to peak at 3.2% on May 25. Daily acute-care and ICU-care hospital admissions and occupancy were forecast accurately and precisely. By October 15, 2020, the basic reproduction number R0 had varied between 1.07-2.78, and 50.8% of the population were estimated to have been infected (1.43 million infections). The proportion of actual infections diagnosed was estimated at 11.6%. Applying the concept of Rt tuning, gradual easing of restrictions was rationalized and justified to start on June 15, 2020, when Rt declined to 0.7, to buffer the increased interpersonal contact with easing of restrictions and to minimize the risk of a second wave. No second wave has materialized as of October 15, 2020, five months after the epidemic peak. ConclusionsUse of modeling and forecasting to guide the national response proved to be a successful strategy, reducing the toll of the epidemic to a manageable level for the healthcare system.
RESUMEN
BackgroundQatar experienced a large severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic that disproportionately affected the craft and manual workers (CMWs) who constitute 60% of the population. This study aimed to investigate level of immunity in communities within this population as well as infection exposure required to achieve herd immunity. MethodsAnti-SARS-CoV-2 seropositivity was assessed in ten CMW communities between June 21 and September 9, 2020. PCR positivity, infection positivity (antibody and/or PCR positive), and infection severity rate were also estimated. Associations with anti-SARS-CoV-2 positivity were investigated using regression analyses. ResultsStudy included 4,970 CMWs who were mostly men (95.0%) and <40 years of age (71.5%). Seropositivity ranged from 54.9% (95% CI: 50.2-59.4%) to 83.8% (95% CI: 79.1-87.7%) in the different CMW communities. Pooled mean seropositivity across all communities was 66.1% (95% CI: 61.5-70.6%). PCR positivity ranged from 0.0% to 10.5% (95% CI: 7.4-14.8%) in the different CMW communities. Pooled mean PCR positivity was 3.9% (95% CI: 1.6-6.9%). Median cycle threshold (Ct) value was 34.0 (range: 15.8-37.4)--majority (79.5%) of PCR-positive individuals had Ct value >30 indicative of earlier rather than recent infection. Infection positivity (antibody and/or PCR positive) ranged from 62.5% (95% CI: 58.3-66.7%) to 83.8% (95% CI: 79.1-87.7%) in the different CMW communities. Pooled mean infection positivity was 69.5% (95% CI: 62.8-75.9%). Only five infections were ever severe and one was ever critical--an infection severity rate of 0.2% (95% CI: 0.1-0.4%). ConclusionsBased on an extended range of epidemiological measures, active infection is rare in these communities with limited if any sustainable infection transmission for clusters to occur. At least some CMW communities in Qatar have reached or nearly reached herd immunity for SARS-CoV-2 infection at a proportion of ever infection of 65-70%.