Original Research
26 March 2024

Evaluation of Strategies for Transitioning to Annual SARS-CoV-2 Vaccination Campaigns in the United StatesFREE

Publication: Annals of Internal Medicine
Volume 177, Number 5
Visual Abstract. Evaluation of Strategies for Transitioning to Annual SARS-CoV-2 Vaccination Campaigns in the United States
The U.S. Food and Drug Administration has proposed administering annual SARS-CoV-2 vaccines. This study used a model of infectious disease transmission to evaluate the effectiveness of such a campaign, quantify the health and economic benefits of a second dose provided to children younger than 2 years and adults aged 50 years or older, and optimize the timing of the second dose.

Abstract

Background:

The U.S. Food and Drug Administration has proposed administering annual SARS-CoV-2 vaccines.

Objective:

To evaluate the effectiveness of an annual SARS-CoV-2 vaccination campaign, quantify the health and economic benefits of a second dose provided to children younger than 2 years and adults aged 50 years or older, and optimize the timing of a second dose.

Design:

An age-structured dynamic transmission model.

Setting:

United States.

Participants:

A synthetic population reflecting demographics and contact patterns in the United States.

Intervention:

Vaccination against SARS-CoV-2 with age-specific uptake similar to that of influenza vaccination.

Measurements:

Incidence, hospitalizations, deaths, and direct health care cost.

Results:

The optimal timing between the first and second dose delivered to children younger than 2 years and adults aged 50 years or older in an annual vaccination campaign was estimated to be 5 months. In direct comparison with a single-dose campaign, a second booster dose results in 123 869 fewer hospitalizations (95% uncertainty interval [UI], 121 994 to 125 742 fewer hospitalizations) and 5524 fewer deaths (95% UI, 5434 to 5613 fewer deaths), averting $3.63 billion (95% UI, $3.57 billion to $3.69 billion) in costs over a single year.

Limitations:

Population immunity is subject to degrees of immune evasion for emerging SARS-CoV-2 variants. The model was implemented in the absence of nonpharmaceutical interventions and preexisting vaccine-acquired immunity.

Conclusion:

The direct health care costs of SARS-CoV-2, particularly among adults aged 50 years or older, would be substantially reduced by administering a second dose 5 months after the initial dose.

Primary Funding Source:

Natural Sciences and Engineering Research Council of Canada, Notsew Orm Sands Foundation, National Institutes of Health, Centers for Disease Control and Prevention, and National Science Foundation.
After the initial rollout of vaccines to curb the global burden of COVID-19, many countries are administering boosters to address waning immunity and alleviate the severity of new and highly transmissible variants of SARS-CoV-2 (1). In the United States, timelines of booster vaccination have changed since the emergence of the Omicron variant, reducing from an initial recommendation of 6 months after the completion of the primary series or a known infection to 2 months when bivalent booster vaccination became available (2). To formalize the frequency of booster doses, the U.S. Food and Drug Administration (FDA) has proposed annual, single-dose vaccination for SARS-CoV-2, similar to influenza vaccination (3), with a potential second dose for those at risk for severe outcomes, including children younger than 2 years and adults aged 50 years or older (4).
The seasonal patterns for SARS-CoV-2 observed in various geographic regions and countries are driven by multiple factors ranging from the emergence of new variants to heterogeneity in subnational vaccination coverage, as well as other public health responses (5–8). These patterns may change from year to year, but SARS-CoV-2 could exhibit annual cycles similar to those of seasonal influenza once it transitions to an endemic state (5). A synchronized pattern between the 2 diseases suggests that, as with influenza, vaccination campaigns against SARS-CoV-2 before an anticipated surge would reduce the disease burden. In the long term, coadministration of vaccines for SARS-CoV-2 and seasonal influenza is expected to become a preferred strategy. However, the effectiveness of this strategy remains undetermined, with unknown timing of a surge and the possibility of semiannual COVID-19 epidemics.
Despite wide availability of messenger RNA (mRNA) bivalent vaccines since September 2022, only 17% of the U.S. population has received a booster dose (9). A shift to annual campaigns may enhance uptake of bivalent boosters toward the uptake seen with influenza vaccination. To evaluate the effectiveness of annual campaigns, we developed an age-structured dynamic model of infectious disease transmission and parameterized it with estimates of the epidemiologic characteristics of SARS-CoV-2 and effectiveness of mRNA vaccines. The primary simulation used the FDA-proposed annual vaccination campaign with a second dose for children younger than 2 years and adults aged 50 years or older, assuming an age-specific uptake similar to that of influenza vaccination. We explored alternative scenarios where the second dose was distributed to the following 3 age groups of adults: 65 years or older, 50 to 64 years, or 18 to 49 years. We used incidence of infection, hospitalizations, deaths, and direct health care costs as measured outcomes to compare the 2-dose vaccination strategies versus an annual single-dose campaign and determine their mitigating effect over a 1-year time horizon as well as the optimal timing of a second dose.

Methods

Model Structure

We constructed a dynamic model of infectious disease transmission using contact patterns between age-stratified subpopulations to simulate COVID-19 incidence, hospitalization, and death under each vaccination strategy for the U.S. population (10). To account for the seasonality in infection incidence, we integrated a mathematical function into the model that amplifies and condenses transmission during certain periods over the course of a year. The epidemiologic states included in the model are susceptible, latent infection, infectious, and recovered (Supplement Table 1). Naturally acquired immunity and its waning were informed by reported changes in the temporal dynamics of the efficacy against reinfection of Omicron BA.1 (1). In our model, after completing the infectious period, individuals transition among 5 states of immunity (“recovered compartments”) that collectively capture the waning of natural immunity against infection and severe disease over time (Supplement Methods). We similarly modeled vaccine-acquired immunity using 3 compartments to incorporate the waning of vaccine-acquired immunity (11–29). Therefore, in addition to age, the population is stratified on the basis of immune status: no protective immunity, vaccine-acquired immunity, waned natural immunity against infection but still protected against severe disease, and natural immunity against both infection and severe disease (Supplement Methods). The extent of natural immunity in each age group was informed by a seroprevalence study done in the United States between September 2021 and February 2022 (30).
Estimates suggest that most of the population has had natural SARS-CoV-2 infection or vaccination against COVID-19 (31). This immune priming would likely increase the proportion of persons with asymptomatic or mild symptomatic cases who may not self-isolate or seek medical attention. Because our study focuses on disease burden using hospitalization, death, and direct health care costs, we did not explicitly model the presymptomatic period, asymptomatic infections, or control measures like self-isolation and quarantine. However, the modeled projections of incidence and hospitalization were calibrated to reflect observed epidemiologic trends (Supplement Methods). Thus, our model implicitly accounts for the population effects of both humoral and cellular immune dynamics after infection and vaccination, as well as behavioral confounding factors that may influence the likelihood of exposure and subsequent infection.

Vaccination Strategies

To calibrate model parameters, we used a continual booster vaccination strategy (allowing boosters to be given over time) with an overall 20% uptake of bivalent boosters based on reported trends between 1 September 2022 and 15 February 2023 (Supplement Figure 1). This uptake was modeled using an age-specific constant vaccination rate over time (Supplement Table 2). We chose this strategy for the model calibration to reflect the vaccination dynamics seen before introduction of annual SARS-CoV-2 vaccination in fall 2023.
Using the calibrated model parameters, we simulated 5 annual vaccination strategies assuming an uptake similar to that of influenza vaccination. The first is an annual single-dose vaccination campaign as the baseline, and the second is this campaign’s expansion to include a second dose for children younger than 2 years and adults aged 50 years or older, as proposed by the FDA. To examine the shift in disease burden as a result of distributing a second dose to alternative age groups, in the remaining 3 simulated vaccination campaigns we provided a second dose to the following groups: in the third strategy, adults aged 65 years or older only; in the fourth, adults aged 50 to 64 years only; and in the fifth, adults aged 18 to 49 years (Table 1). For all scenarios, we assumed that the vaccination rate and vaccine uptake of the second dose are equivalent to those described for the first dose. For the scenarios offering a second dose, the additional dose was offered at least 90 days after the initial dose.
Table 1. Description of Vaccination Scenarios Simulated
Vaccination ScenarioDescription of the Campaign
AnnualAnnual single-dose vaccination campaign with an age-stratified, influenza-like vaccine uptake
FDA-proposedAnnual single-dose vaccination campaign with a second dose for children aged <2 y and adults aged ≥50 y
Annual with second dose among ≥65Annual single-dose vaccination campaign with a second dose for only adults aged ≥65 y
Annual with second dose among 50–64Annual single-dose vaccination campaign with a second dose for only adults aged 50–64 y
Annual with second dose among 18–49Annual single-dose vaccination campaign with a second dose for only adults aged 18–49 y
FDA = U.S. Food and Drug Administration.
We assumed that SARS-CoV-2 vaccine uptake and timing of vaccination matched those of a typical vaccination campaign for seasonal influenza. We applied the vaccination rate and uptake for 6 age groups—6 months to 4 years, 5 to 12 years, 13 to 17 years, 18 to 49 years, 50 to 64 years, and 65 years or older—that were obtained from least-squares fitting to data from 12 influenza seasons (Supplement Figure 2). Vaccination uptake in different age groups for the single-dose campaign was sampled across the range of uptakes observed for influenza vaccination between the 2012-to-2013 and 2021-to-2022 seasons in the United States (Supplement Methods and Supplement Figures 2 and 3). To reduce computational intensity and to simplify interpretation (that is, we avoided making assumptions about the distribution of preexisting vaccine-acquired immunity among those intending or not intending to vaccinate across age groups over the course of the campaign), the model results assumed that no individual has prior vaccine-acquired immunity, thereby maximizing vaccine benefits in all of the strategies in reducing incidence but preserving the comparative benefits of alternative strategies.

Parameterization

Model parameters for the transmission rate, infectious period, and other disease-specific characteristics are based on available estimates for Omicron subvariants (Supplement Table 2). We considered age-specific susceptibility to infection, prior natural immunity, probability of hospitalization, and probability of death given hospitalization for SARS-CoV-2 infection, as well as vaccination uptake for both influenza and SARS-CoV-2 (Supplement Table 2). Vaccine effectiveness against infection and severe outcomes was informed by temporal data on waning immunity against the Omicron variant from studies of both monovalent and bivalent vaccines (Supplement Figures 4 and 5) (11–29). Because of potential bias in these data, we explored faster and slower waning of vaccine efficacy. The effectiveness of natural immunity in protecting against infection and severe disease was informed by results from a meta-analysis on the Omicron BA.1 variant (32).
To derive scenario outcomes, we used a Latin hypercube sampling technique (33) to generate samples of model parameters from uniform distributions (Supplement Table 2). We then generated 500 000 epidemiologic trajectories from 1 September for 12 consecutive months. Next, we applied a Monte Carlo sampling approach to select epidemiologic trajectories with an initial peak in hospital admission occurring between 1 September and 31 March and a subsequent peak between 1 April and 31 August. We assigned a greater selection weight to the timing of winter peaks from 1 December to 1 March and summer peaks from 1 June to 31 August (Supplement Methods). Based on observed patterns during the COVID-19 pandemic (5), we considered trajectories with a larger winter peak than summer peak (Supplement Figure 6). For comparison purposes, we also stratified the parameter samples to produce either a larger summer peak (Supplement Figure 7) or a single peak in the winter (Supplement Figure 8). In the latter scenario, we considered trajectories with a peak time between 1 October and 30 April, with a weighted preference from the beginning of December to the end of February (Supplement Methods).

Direct Health Care Cost

We calculated the direct health care cost in various age groups for disease outcomes (Supplement Table 2), consisting of outpatient care (office visits or emergency department visits), inpatient care (hospitalization) with recovery, and inpatient care with death (34, 35). The average costs among inpatients account for duration of stay, admission to the intensive care unit, and use of mechanical ventilation (34). Emergency department visits without hospital admission were considered outpatient care (36).

Estimating Benefits of a Second Dose

To quantify the benefits of a second dose, we computed the absolute differences in cumulative incidence, hospitalization, death, and direct health care costs between the FDA-proposed and annual campaign scenarios. We applied the same approach to quantify the benefits of providing a second vaccine dose to individuals aged 65 years or older, 50 to 64 years, and 18 to 49 years compared with the annual campaign.

Model Implementation

The model simulations and analysis were done in MATLAB R2022a (MathWorks). The results are presented as the mean and its 95% uncertainty interval (UI) from 2500 bootstraps of the filtered model output. Computational code is available in an online repository (37).

Role of the Funding Source

The funding sources had no role in the design, conduct, or analysis of the study or the decision to submit the manuscript for publication.

Results

Transition to an Annual Vaccination Campaign

Our results suggest that transition to an annual campaign from a continual booster campaign would provide a moderate reduction in the disease burden among adults aged 50 years or older (Supplement Results). Under an annual campaign with uptake similar to that of influenza vaccination, annual cumulative estimates for the U.S. population were 1 037 647 hospitalizations (95% UI, 1 017 724 to 1 057 333 hospitalizations) and 40 671 deaths (95% UI, 39 836 to 41 533 deaths) (Figure 1, B and C). The resulting total direct health care costs were estimated to be $30.47 billion (95% UI, $29.89 billion to $31.04 billion) (Figure 1, D). Among the age groups, adults aged 65 years or older had the greatest number of hospitalizations, number of deaths, and associated costs per capita, whereas those aged 18 to 64 years carried the largest incidence per capita (Figure 1, E to H).
Figure 1. Effectiveness of an annual single-dose campaign and the FDA-proposed campaign.
Assuming an influenza-like vaccine uptake for the annual SARS-CoV-2 vaccination campaign with a single dose (white; annual) and a campaign with a second dose 150 d after the first dose (green; FDA-proposed), we estimated the overall incidence (A), hospitalizations (B), deaths (C), and direct health care costs (D) per 10 000 persons in the population. Panels E–H correspond to age-specific estimates per 10 000 persons in the population. FDA = U.S. Food and Drug Administration.

Benefits of the FDA-Proposed Campaign

The largest benefit of a second dose in reducing the overall disease burden and direct health care costs estimated in the annual campaign was associated with a time interval of 150 days between the 2 doses in the FDA-proposed campaign (Figure 2). However, this time interval varied when maximizing the reduction of outcomes and health care costs among different age groups (Figure 2, H). For example, the largest reduction in health care costs among individuals aged 18 to 49 years was associated with a 120-day interval between the 2 doses.
Figure 2. Benefits of a second dose under the FDA-proposed campaign.
Providing a second dose of vaccine to children aged <2 y and adults aged ≥50 y, 90–300 d after their initial dose, we estimated the reduction in incidence (A), hospitalizations (B), deaths (C), and direct health care costs (D) per 10 000 persons in the population compared with the annual single-dose vaccination campaign. Panels E–H correspond to age-specific estimates for reduction of outcomes and health care costs per 10 000 persons in the population. FDA = U.S. Food and Drug Administration.
Compared with the annual campaign, the FDA-proposed campaign with a 150-day dosing interval resulted in 123 869 fewer hospitalizations (95% UI, 121 994 to 125 742 fewer hospitalizations) and 5524 fewer deaths (95% UI, 5434 to 5613 fewer deaths), generating a savings of $3.63 billion (95% UI, $3.57 billion to $3.69 billion) in direct health care costs (Figures 1 and 2).

Benefits of a Second Dose Among Different Age Groups

The time interval between the 2 doses that resulted in the largest reduction in direct health care costs was estimated to be 180 days for the annual campaign with a second dose to adults aged 65 years or older. When the second dose was administered to individuals aged either 50 to 64 years or 18 to 49 years, a dosing interval of 120 days offered the largest reduction in direct health care costs (Table 2; Supplement Figures 9 to 11). However, we note that the difference in the outcome associated with a 150-day dosing schedule is marginal (Supplement Figures 9 to 11). At the optimal dosing intervals, we estimated that health care costs incurred from the annual campaign will be reduced by $1.81 billion (95% UI, $1.78 billion to $1.84 billion) by administering a second dose to those aged 65 years or older, by $2.07 billion (95% UI, $2.04 billion to $2.11 billion) with a second dose to those aged 50 to 64 years, and by $2.37 billion (95% UI, $2.32 billion to $2.41 billion) with a second dose to those aged 18 to 49 years (Table 2). The FDA-proposed campaign outperformed the 3 alternative second-dose campaigns in reducing outcomes and health care costs (Table 2).
Table 2. Estimated Outcomes and Their 95% UIs for Simulated Vaccination Scenarios Over a 1-Year Time Horizon
Vaccination ScenarioIncidence (95% UI), n (millions)Hospitalizations (95% UI), n (hundred thousands)Deaths (95% UI), n (ten thousands)Direct Health Care Costs (95% UI), $ (billions)Optimal Time Interval Between Doses, d
Annual164.44 (161.04–167.73)10.38 (10.18–10.57)4.07 (3.98–4.15)30.47 (29.89–31.04)
FDA-proposed153.22 (149.87–156.76)9.14 (8.95–9.34)3.52 (3.43–3.60)26.84 (26.25–27.42)150
Annual with second dose among ≥65161.75 (158.22–165.10)9.74 (9.55–9.95)3.72 (3.64–3.80)28.67 (28.10–29.26)180
Annual with second dose among 50–64155.73 (152.18–159.23)9.68 (9.47–9.88)3.80 (3.72–3.89)28.41 (27.81–29.00)120
Annual with second dose among 18–49153.67 (150.25–157.05)9.57 (9.38–9.78)3.79 (3.71–3.88)28.10 (27.52–28.71)120
FDA = U.S. Food and Drug Administration; UI = uncertainty interval.

Secondary and Sensitivity Analyses

We compared the FDA-proposed campaign versus the annual campaign by varying several parameters and assumptions of the model, including a single winter peak or a larger summer peak of hospitalizations, reduced daily vaccination rates and overall uptake, decreased transmissibility of the virus, delay in SARS-CoV-2 primary vaccination relative to the time of influenza vaccination, higher vaccine efficacy against infection and severe disease, and different rates of waning of vaccine-induced immunity (Supplement Table 3). The optimal dosing interval decreased from 150 days to 120 days (relative to annual influenza vaccination) when the daily vaccination rate was reduced by 33% or 66%, the uptake of SARS-CoV-2 vaccine was lowered by 33% or 66%, the efficacy against infection was decreased by 66%, or SARS-CoV-2 vaccination was delayed by 28 days relative to influenza vaccination among 41% or 64% of those intending to vaccinate. In a scenario where only the second-dose uptake was reduced by 33% or 66%, the optimal dosing interval increased to 180 days, which can be attributed to the interplay among the uptake of the second dose, waning vaccine immunity, and population-level indirect protection. Assuming that vaccine-acquired immunity wanes in all age groups at a similar rate to that estimated for persons younger than 18 years, the optimal dosing interval was estimated to be 120 days. This decline in the timing of the second dose can be attributed to the reduced vaccine efficacy and accelerated waning estimated for those younger than 18 years relative to those aged 60 years or older, requiring the boost in immunity sooner among the vulnerable population to maintain immunity. The shortest dosing interval was estimated to be 90 days in the scenario where SARS-CoV-2 epidemiologic trends transition to a single winter peak.

Discussion

In early 2023, the FDA reviewed a proposal advocating a transition to annual SARS-CoV-2 vaccinations (4). The proposal recommends a single dose for most individuals with a second dose for children younger than 2 years and adults aged 50 years or older (4). Using an age-structured dynamic model of infectious disease transmission calibrated to replicate winter and late summer peaks in COVID-19 hospitalization, we evaluated the effectiveness of the proposed annual vaccination with an uptake similar to that of influenza vaccination. We also estimated the optimal interval between the first and second doses that minimizes the direct health care costs. Our analysis showed that transitioning to an annual campaign would moderately reduce disease burden among adults aged 50 years or older. In comparison, the FDA-proposed campaign would lead to a 15% reduction in hospitalizations and an 18% decrease in deaths compared with the annual campaign. Assuming a second peak in hospitalizations, our model found that the FDA-proposed campaign yields the greatest benefit when the second dose is administered 5 months after the first dose, with diminishing returns beyond a 6-month dosing interval. Exploring the distribution of second doses among age groups, our findings suggest that adopting the FDA-proposed campaign is the most effective strategy of those examined by our model to mitigate the burden of SARS-CoV-2 in the United States.
We found that the FDA-proposed campaign with a second dose administered 5 months after the primary dose produced the largest reduction in direct health care costs compared with the annual campaign. However, we assumed that the vaccination rate for the first and second doses was equivalent to that estimated for influenza vaccination. Scenario analyses illustrated that the optimal time interval between the 2 doses is sensitive to vaccine uptake and the waning rate of vaccine-acquired immunity. As of 9 December 2023, SARS-CoV-2 vaccine uptake was 16%, whereas influenza vaccine uptake had already reached 42% (38–41), potentially influencing the dosing interval. As expected, a shorter dosing interval becomes crucial to counteract accelerated waning immunity. When preexisting vaccine-acquired immunity (which we initially assumed to be absent) is considered, we expect the suggested dosing interval to extend beyond that found in our baseline analysis. Preexisting vaccine-acquired immunity could delay the surge and mitigate the fall and winter disease burden, enhancing the effectiveness of the first dose over a longer time interval. Although previous studies propose a frequency of 6 to 12 months for SARS-CoV-2 booster vaccination (42, 43), particularly among those aged 75 years or older (44), our analysis indicates a 5-month dosing interval in the FDA-proposed campaign, with a potential range of 3 to 6 months. This timing is projected to have the largest effect on reducing direct health care costs.
Within the framework of an annual SARS-CoV-2 vaccination initiative, our analysis highlights a moderate reduction in disease burden for the adult population aged 50 years or older on transitioning to an annual campaign. The FDA-proposed campaign, targeting this vulnerable population and children younger than 2 years, emerges as the strategy with the lowest direct health care costs among alternative strategies investigated. However, the second-dose uptake in the prioritized age groups was assumed to be 100% among those receiving the first dose. In a scenario with a 33% reduction in second-dose uptake and the optimal dosing interval of 6 months, the direct health care costs averted decreased by 47%. Among alternative vaccination strategies, we found that prioritizing adults aged either 18 to 49 years or 50 to 64 years with a second dose was more effective in reducing direct health care costs than providing second doses to only adults aged 65 years or older because of differences in population-level vaccine immunity, extent of direct protection, and contact mixing across age-stratified groups. Of note, we found that the age group selected for a second dose can influence the dosing interval, likely due to the effect of these contact patterns. Thus, if some of the prioritized populations in the FDA-proposed campaign are reluctant to pursue a second dose, then offering second doses to individuals aged 18 to 49 years could compensate for this uptake reduction by providing indirect protection for older adults.
The temporal dynamics of immunity against infection and severe disease are expected to change with the evolution of SARS-CoV-2. Our model was informed by the temporal changes in individual-level immunity against infection and severe disease using estimates of the waning immune protection from prior infection or vaccination (11–29, 32). The data from existing epidemiologic studies inherently account for the effects of and changes in both humoral and cellular immunity after infection and vaccination, as well as behavioral confounding variables that may influence the likelihood of exposure and subsequent infection. Previous studies suggest that maintaining a robust cellular immune response to SARS-CoV-2 reduces the risk for severe disease and death, with the humoral response playing a primary role in protecting against infection (43, 45, 46). Our formulation of waning immunity implicitly captures the effect of humoral and cellular immunity through parameterization and transition between states of immunity in the model.
Our analysis of age-specific waning of vaccine-acquired immunity shows a slower waning and higher protection against severe disease among those aged 60 years or older than among younger age groups. This result likely reflects potential biases in the data used to estimate vaccine efficacy. Specifically, observations related to hospitalization were from persons who had received 2 or 3 doses of monovalent vaccine in a test-negative case–control study in England (18). A potential bias pertains to the occurrence of “incidental” cases in hospitals, where patients admitted for reasons unrelated to COVID-19 subsequently tested positive for SARS-CoV-2, resulting in lower estimates of vaccine efficacy against severe disease (47). The occurrence of incidental cases in the hospital has been more pronounced among persons aged 18 to 64 years than among those aged 65 or older (47). In an effort to alleviate the effect of this bias, we did scenario analyses by considering both fast and slow rates of waning vaccine-acquired immunity.
A strength of our study is the construction of a model that uses the U.S. demographics and age-stratified contact patterns and includes naturally acquired and vaccine-induced immunity with waning, age-specific vaccination uptake, and administration of a second dose with consideration of SARS-CoV-2 seasonal patterns. However, these factors vary among countries and even states within the United States. In the scenario of semiannual epidemic peaks, uncertainties arise regarding how each of these factors and the practice of nonpharmaceutical interventions might influence the incremental benefit and optimal timing of the second dose. Moreover, the population-based model does not account for the extent of individual variation in susceptibility to infection (for example, immune compromise) beyond the age-stratified integration. We found that reducing transmission or the probability of hospitalization decreased the effectiveness of the FDA-proposed campaign. Thus, consistent with prior studies (48), if new immune-evasive variants emerge, vaccinating the elderly population with a second dose or potentially a new variant-specific vaccine may be critical in reducing hospitalizations and direct health care costs.
Previous analyses suggest that COVID-19 epidemic peaks will likely coincide with those of other respiratory diseases, such as seasonal influenza and respiratory syncytial virus disease, in many countries (5). Should epidemiologic trends of SARS-CoV-2 fully adopt seasonal dynamics akin to those of influenza, we anticipate that the significance of a second dose in mitigating disease burden will diminish.
In conclusion, our study shows that adopting an annual vaccination campaign with the provision of a second dose to children younger than 2 years and adults aged 50 years or older can be a suitable approach to protect individuals against SARS-CoV-2 infection and associated outcomes. Monitoring the seasonal and evolutionary patterns of SARS-CoV-2 is critically important to inform decisions on vaccination strategies and the development of new vaccines to maintain population immunity.

Supplemental Material

Supplementary Material

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Information & Authors

Information

Published In

cover image Annals of Internal Medicine
Annals of Internal Medicine
Volume 177Number 5May 2024
Pages: 609 - 617

History

Published online: 26 March 2024
Published in issue: May 2024

Keywords

Authors

Affiliations

Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, Connecticut (C.R.W., A.P., A.P.G.)
Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, Connecticut (C.R.W., A.P., A.P.G.)
Agent-Based Modelling Laboratory, York University, Toronto, Ontario, Canada (S.M.M.)
Meagan C. Fitzpatrick, PhD https://orcid.org/0000-0002-5248-2668
Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, Maryland (M.C.F.)
Burton H. Singer, PhD
Emerging Pathogens Institute, University of Florida, Gainesville, Florida (B.H.S.).
Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, Connecticut (C.R.W., A.P., A.P.G.)
Financial Support: Dr. Moghadas received support from the Natural Sciences and Engineering Research Council of Canada (Mathematics for Public Health program, Discovery Grant, and Alliance Grant). Dr. Galvani received support from the Notsew Orm Sands Foundation, National Institutes of Health grant R01 AI151176, Centers for Disease Control and Prevention grants U01IP001136 and U01IP001136-Suppl, and National Science Foundation Expeditions grant 1918784. Dr. Fitzpatrick received support from National Institutes of Health grant 5K01 AI141576.
Reproducible Research Statement: Study protocol: Not applicable. Statistical code: Available in an online repository (37). Data set: Model input data and parameter calibration are available in an online repository (37).
Corresponding Author: Alison P. Galvani, PhD, Yale Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, 135 College Street, Suite 200, New Haven, CT 06510; e-mail, [email protected].
Author Contributions: Conception and design: M.C. Fitzpatrick, A.P. Galvani, A. Pandey, B.H. Singer.
Analysis and interpretation of the data: M.C. Fitzpatrick, A.P. Galvani, S.M. Moghadas, A. Pandey, B.H. Singer, C.R. Wells.
Drafting of the article: A.P. Galvani, A. Pandey, B.H. Singer, C.R. Wells.
Critical revision for important intellectual content: M.C. Fitzpatrick, A.P. Galvani, S.M. Moghadas, A. Pandey, B.H. Singer, C.R. Wells.
Final approval of the article: M.C. Fitzpatrick, A.P. Galvani, S.M. Moghadas, A. Pandey, B.H. Singer, C.R. Wells.
Statistical expertise: S.M. Moghadas, A. Pandey, B.H. Singer.
Obtaining of funding: A.P. Galvani, S.M. Moghadas.
Administrative, technical, or logistic support: S.M. Moghadas.
Collection and assembly of data: A. Pandey, C.R. Wells.
This article was published at Annals.org on 26 March 2024.

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Chad R. Wells, Abhishek Pandey, Seyed M. Moghadas, et al. Evaluation of Strategies for Transitioning to Annual SARS-CoV-2 Vaccination Campaigns in the United States. Ann Intern Med.2024;177:609-617. [Epub 26 March 2024]. doi:10.7326/M23-2451

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