Impact of accelerating booster vaccination amidst Omicron surge in the United States

COVID-19 infections driven by the Omicron variant are sweeping across the United States. Although early evidence suggests that the Omicron variant may cause less severe disease than previous variants, the explosive spread of infections threatens to drive hospitalizations and deaths to unprecedented high levels, swamping already overburdened hospitals. Booster vaccination appears to be effective at preventing severe illness and hospitalization. However, the pace of booster vaccination in the US has been slow despite the available infrastructure to administer doses at a much higher rate. We used an age-stratified, multi-variant agent-based model to project the reduction in COVID-related deaths and hospitalizations that could be achieved by accelerating the current daily pace of booster vaccination in the US. We found that doubling the rate of booster vaccination would prevent over 400,000 hospitalizations and 48,000 deaths. Tripling the booster vaccination rate would avert over 600,000 hospitalizations and save 70,000 lives during the first four months of 2022.

Lives saved and hospitalizations averted by COVID-19 vaccination in New York City

Despite the emergence of highly transmissible variants, the number of cases in NYC has fallen from over 5,500 average daily cases in January, 2020 to less than 350 average daily cases in July, 2021. The impact of vaccination in saving lives and averting hospitalizations in NYC has not been formally investigated yet. We used an age-stratified agent-based model calibrated to COVID-19 transmission and vaccination in NYC to evaluate the impact of the vaccination campaign in suppressing the COVID-19 burden. We found that the vaccination campaign has prevented over 250,000 COVID-19 cases, 44,000 hospitalizations and 8,300 deaths from COVID-19 infection since the start of vaccination through July 1, 2021. Notably, the swift vaccine rollout suppressed another wave of COVID-19 that would have led to sustained increase in cases, hospitalizations and deaths during spring triggered by highly transmissible variants. As the Delta variant sweeps across the city, the findings of this study underscore the urgent need to accelerate vaccination and close the vaccine coverage gaps across the city.

COVID-19 deaths and hospitalizations averted by rapid vaccination rollout in the United States

ImportanceRandomized clinical trials have shown that the COVID-19 vaccines currently approved in the US are highly efficacious. However, more evidence is needed to understand the population-level impact of the US vaccination rollout in the face of the changing landscape of COVID-19 pandemic in the US, including variants with higher transmissibility and immune escape. ObjectiveTo quantify the population-level impact of the US vaccination campaign in averting cases, hospitalizations and deaths from December 12, 2020 to June 28, 2021. DesignAge-stratified agent-based model which included transmission dynamics of the Alpha, Gamma and Delta variants in addition to the original Wuhan-1 variant. SettingOur model was calibrated to COVID-19 outbreak and vaccine rollout in the US. Model predictions were made at the country level. ParticipantsSimulated age-stratified population representing US demographics. Main Outcomes and MeasuresCases, hospitalizations and deaths averted by vaccination against COVID-19 in the US, compared to the counterfactuals of no vaccination and vaccination administered at half the actual pace. ResultsThe swift vaccine rollout in the US curbed a potential resurgence of cases in April 2021, which would have been otherwise fuelled by the Alpha variant. Compared to the scenario without vaccines, we estimated that the actual vaccination program averted more than 26 million cases, 1.2 million hospitalizations and saved 279,000 lives. A vaccination campaign with half the actual rollout rate would have led to an additional 460,000 hospitalizations and 121,000 deaths. Conclusions and RelevanceThe COVID-19 vaccination campaign in the US has had an extraordinary impact on reducing disease burden despite the emergence of highly transmissible variants. These findings highlight that the pace of vaccination was essential for mitigating COVID-19 in the US, and underscore the urgent need to close the vaccine coverage gaps in communities across the country. Key PointsO_ST_ABSQuestionC_ST_ABSHow effective was the United States (US) vaccination campaign in suppressing COVID-19 burden? FindingsThe vaccination campaign was highly effective in curbing the COVID-19 outbreak in the US. We estimated that the vaccine rollout saved over 275,000 lives and averted 1.2 million hospitalizations. MeaningThe swift vaccine rollout in the US averted a remarkable number of cases, hospitalizations and deaths despite the emergence of highly transmissible variants.

Quantifying the potential for dominant spread of SARS-CoV-2 variant B.1.351 in the United States

Recent evidence suggests that some new SARS-CoV-2 variants with spike mutations, such as P.1 (Gamma) and B.1.617.2 (Delta), exhibit partial immune evasion to antibodies generated by natural infection or vaccination. By considering the Gamma and Delta variants in a multi-variant transmission dynamic model, we evaluated the dominance of these variants in the United States (US) despite mounting vaccination coverage and other circulating variants. Our results suggest that while the dominance of the Gamma variant is improbable, the Delta variant would become the most prevalent variant in the US, driving a surge in infections and hospitalizations. Our study highlights the urgency for accelerated vaccination and continued adherence to non-pharmaceutical measures until viral circulation is driven low.

Evaluation of COVID-19 vaccination strategies with a delayed second dose

Two of the COVID-19 vaccines currently approved in the United States require two doses, administered three to four weeks apart. Constraints in vaccine supply and distribution capacity, together with a deadly wave of COVID-19 from November 2020 to January 2021 and the emergence of highly contagious SARS-CoV-2 variants, sparked a policy debate on whether to vaccinate more individuals with the first dose of available vaccines and delay the second dose, or to continue with the recommended two-dose series as tested in clinical trials. We developed an agent-based model of COVID-19 transmission to compare the impact of these two vaccination strategies, while varying the temporal waning of vaccine efficacy following the first dose and the level of pre-existing immunity in the population. Our results show that for Moderna vaccines, a delay of at least 9 weeks could maximize vaccination program effectiveness and avert at least an additional 17.3 (95% CrI: 7.8 - 29.7) infections, 0.71 (95% CrI: 0.52 - 0.97) hospitalizations, and 0.34 (95% CrI: 0.25 - 0.44) deaths per 10,000 population compared to the recommended 4-week interval between the two doses. Pfizer-BioNTech vaccines also averted an additional 0.61 (95% CrI: 0.37 - 0.89) hospitalizations and 0.31 (95% CrI: 0.23 - 0.45) deaths per 10,000 population in a 9-week delayed second dose strategy compared to the 3-week recommended schedule between doses. However, there was no clear advantage of delaying the second dose with Pfizer-BioNTech vaccines in reducing infections, unless the efficacy of the first dose did not wane over time. Our findings underscore the importance of quantifying the characteristics and durability of vaccine-induced protection after the first dose in order to determine the optimal time interval between the two doses.

Multifaceted strategies for the control of COVID-19 outbreaks in long-term care facilities in Ontario, Canada

The novel coronavirus disease 2019 (COVID-19) has caused severe outbreaks in Canadian long-term care facilities (LTCFs). In Canada, over 80% of COVID-19 deaths during the first pandemic wave occurred in LTCFs. We sought to evaluate the effect of mitigation measures in LTCFs including frequent testing of staff, and vaccination of staff and residents. We developed an agent-based transmission model and parameterized it with disease-specific estimates, temporal sensitivity of nasopharyngeal and saliva testing, results of vaccine efficacy trials, and data from initial COVID-19 outbreaks in LTCFs in Ontario, Canada. Characteristics of staff and residents, including contact patterns, were integrated into the model with age-dependent risk of hospitalization and death. Estimates of infection and outcomes were obtained and 95% credible intervals were generated using a bias-corrected and accelerated bootstrap method. Weekly routine testing of staff with 2-day turnaround time reduced infections among residents by at least 25.9% (95% CrI: 23.3% - 28.3%), compared to baseline measures of mask-wearing, symptom screening, and staff cohorting alone. A similar reduction of hospitalizations and deaths was achieved in residents. Vaccination averted 2-4 times more infections in both staff and residents as compared to routine testing, and markedly reduced hospitalizations and deaths among residents by 95.9% (95% CrI: 95.4% - 96.3%) and 95.8% (95% CrI: 95.5% - 96.1%), respectively, over 200 days from the start of vaccination. Vaccination could have a substantial impact on mitigating disease burden among residents, but may not eliminate the need for other measures before population-level control of COVID-19 is achieved.