key: cord-0700604-ldakcvh5
authors: Moghadas, Seyed M; Sah, Pratha; Vilches, Thomas N; Galvani, Alison P
title: Can the USA return to pre-COVID-19 normal by July 4?
date: 2021-06-02
journal: Lancet Infect Dis
DOI: 10.1016/s1473-3099(21)00324-8
sha: a86e3b567371a3f61eeb5b556f076ffd41b86372
doc_id: 700604
cord_uid: ldakcvh5

nan

We stratified the model population into six age groups of 0-4, 5-19, 20-49, 50-64, 65-79, and 80+ years based on US census data. Daily contacts between individuals were sampled from a negative-binomial distribution parameterized using an empirically-determined age-specific contact network. 3 We parameterized the infectivity of asymptomatic, mild symptomatic, and severe symptomatic individuals to be 26%, 44%, and 89% relative to the pre-symptomatic stage. [4] [5] [6] The estimates and distributions of disease-specific parameters are summarized in Table A1 . We assumed that recovery from infection conferred immunity against reinfection for at least one year. A proportion of those with severe disease were hospitalized within 2-5 days of symptom onset. 7, 8 Symptomatic cases who were not hospitalized self-isolated within 24 hours of symptom onset, and reduced their number of daily contacts by an average of 74%. This reduction of contacts was derived from a representative sample population during COVID-19 lockdown. 9 Following recommendations of the Advisory Committee on Immunization Practices (ACIP), vaccine prioritization was set sequentially to: (i) healthcare workers; adults with comorbidities, and those aged 65 and older; (ii) other individuals aged 16-64; and (iii) children between 12 and 15 years of age. 10 Based on vaccine uptake data, we applied an age-dependent prioritization with higher probability of (60%) vaccination within 40-64 age bracket, compared to that (40%) for individuals aged 16-39 for category (ii). 11 The minimum age-eligibility for vaccination was 16 years before May 13, 2021 after which children aged 12 to 15 years became eligible for vaccination. We used the weekly average of reported vaccine doses distributed (per 100,000 population) since the start of vaccination to simulate different scenarios. We considered Moderna and Pfizer-BioNTech vaccines with an interval of 28 and 21 days between the first and second doses. 12, 13 The efficacy of these vaccines against infection, symptomatic disease, and severe disease was parameterized based on published studies and FDA briefing documents (Table A2) . [12] [13] [14] [15] [16] We assumed the same efficacy against both the original strain and the B.1.1.7 variant 17,18 . Table A2 . Estimated vaccine efficacies with associated timelines.

Weeks after the first dose Weeks after the second dose 22 The effect of non-pharmaceutical interventions was accounted for in the calibration process (with a reproduction number of 1.17).

Full details of the model structure can be found in our recent study. 1 The model was computationally implemented in Julia language and is available at: https://github.com/thomasvilches/CDC_guidelines.

CDC guidelines for fully vaccinated individuals were published on April 2, 2021. 23 We, therefore, allowed contacts of vaccinated individuals to change on April 3 while maintaining contact patterns of other individuals the same as those prior to April 2 until July 4th. We also implemented vaccination of children 12 to 15 years of age from May 13, 2021. The model simulated disease spread when vaccinated individuals resumed their pre-pandemic level of social activity either (a) 14 days after the first dose, or (b) 14 days after the second dose, which corresponds to the CDC guidelines for fully vaccinated individuals.

To evaluate the impact of altered contact patterns of all individuals from July 4th in addition to normal activities of vaccinated people, we considered the following scenarios: 1) Unvaccinated individuals resumed their pre-pandemic level of social activity ( Figure A1 ). 2) Unvaccinated individuals increased their social activity to 70% of the pre-pandemic contact behaviour ( Figure A2 ). 3) Unvaccinated individuals increased their social activity to 85% of the pre-pandemic contact behaviour ( Figure A3 ).

We present our results in the Main text and Appendix considering vaccinations with Moderna vaccines. We obtained similar results substituting the base case vaccine parameters for

Moderna vaccines with those for Pfizer-BioNTech vaccines. We further evaluated the return to normal behaviour for all individuals on September 1, 2021. At a daily rate of 2 million vaccine doses, we found that a much lower surge may occur compared to scenarios simulated for July 4 even if social distancing measures are completely lifted (Appendix, Figure A4 ), with substantially lower hospitalization and deaths. Such a surge would be completely prevented if the vaccination rate increased to an average of 3 million doses per day. Figure A1 . Model fit to case incidence data of COVID-19 per 100,000 population in the US, and projected incidence of (A) infection, (B) hospitalizations and (C) deaths, with contacts of vaccinated individuals resuming to the pre-pandemic era 14 days after the first dose (orange curve) or 14 days after the first dose (green curve) from April 3. On July 4, all individuals returned to normal social activity of the pre-pandemic era. Figure A2 . Model fit to case incidence data of COVID-19 in the US, and projected incidence of infection (A), hospitalizations (B), and deaths (C), with contacts of vaccinated individuals resuming to normal social activity of the pre-pandemic era one day after the first dose (orange curve) or 14 days after the first dose (green curve) from April 3. On July 4, all individuals returned to 70% of the pre-pandemic contact behaviour. st Figure A3 . Model fit to case incidence data of COVID-19 in the US, and projected incidence of infection (A), hospitalizations (B), and deaths (C), with contacts of vaccinated individuals resuming to normal social activity of the pre-pandemic era one day after the first dose (orange curve) or 14 days after the first dose (green curve) from April 3. On July 4, all individuals returned to 85% of the pre-pandemic contact behaviour. Figure A4 . Model fit to case incidence data of COVID-19 per 100,000 population in the US, and projected incidence of infection (A), hospitalizations (B) and deaths (C). Contacts of vaccinated individuals resumed to the pre-pandemic era 14 days after the first dose (orange curve) or 14 days after the first dose (green curve) from April 3. On September 1, all individuals returned to normal social activity of the pre-pandemic era.

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