Covid-19 Vaccine and Its Speed and Efficacy

COVID-19 VACCINE SPEED & EFFICACY

Background: The global effort to develop a vaccine for coronavirus disease 2019 (COVID-19) has already produced 2 candidates, each requiring 2 doses, with reported efficacies exceeding 90% (1). The U.S. Food and Drug Administration (FDA) has granted Emergency Use Authorization for both vaccines (Pfizer-BioNTech and Moderna). Their reported efficacies greatly exceed the 50% threshold the FDA cited in a June 2020 guidance document (2). Additional vaccine candidates at earlier stages of development hold the promise of single dosing, simpler storage requirements, and more rapid immunity after vaccination (3).

The two vaccine come during this pandemic covid-19, becomes 2 frontrunner granted by FDA to use  authorization, The multiple vaccine availability welcome the new development of vaccine but lead a policy dilemmas. how to find best vaccine among them and which populations should receive it?

should FDA expect all the candidate to meet or exceed 90% efficacy benchmark established by two frontrunner?

Objective: To quantify the speed-versus-efficacy tradeoff using a previously published model of a COVID-19 vaccination program (4). The model accounts for transmission of severe acute respiratory syndrome coronavirus 2, COVID-19 disease severity, and recovery or vaccination leading to protective immunity. Modifying parameters related to vaccine efficacy, vaccination program scale-up and coverage, and the time to vaccine benefits, we compared the likely performance of 1- and 2-dose vaccine candidates over a 6-month horizon on outcomes of cumulative infections, deaths, and peak hospitalizations.

Methods and Findings: Consistent with the FDA efficacy definition, we assumed that a 2-dose vaccine produced a 95% decrease in rates of progression to symptomatic disease, to severe or critical disease from mild disease, and to COVID-19–related death, as well as a nearly 3-fold increase in rates of disease recovery. We further assumed that this vaccine had a 0.5% daily uptake, double the observed peak rate for influenza vaccination in the United States (4), and took 4 weeks to achieve lifetime protection, allowing for partial immunity after the first dose. We compared this vaccine with 2 hypothetical, single-dose alternatives, one conferring lifetime protection and the other with stable efficacy of uncertain duration (exponentially distributed with a mean duration of 6 months). Both of these single-dose vaccines were assumed to achieve more rapid daily uptake (0.75%) and to take effect 14 days after administration. We considered efficacies for both single-dose vaccines ranging from 0% to 100%.

We did the base analysis in the context of an epidemic with an effective reproduction number (Rt) of 1.8. Other inputs were obtained from published sources, particularly the guidance for COVID-19 model parameterization from the Centers for Disease Control and Prevention and the Department of Health and Human Services Office of the Assistant Secretary for Preparedness and Response (4, 5).

Discussion: Prior work has shown that the success of a COVID-19 vaccination program will depend more on the speed and reach of its implementation than on the efficacy of the vaccine itself (4). The analysis presented here highlights the steep clinical and epidemiologic costs imposed by a 2-dose vaccination series in the context of ongoing pandemic response. Depending on the duration of protection conferred—and, of note, considering only a 6-month time horizon—a single-dose vaccine with 55% effectiveness may confer greater population benefit than a 95%-effective vaccine requiring 2 doses. This suggests that now that a highly effective, 2-dose vaccine for COVID-19 has been authorized and vaccination programs have begun, sustained and aggressive investment in pursuit of faster-acting, more convenient, 1-dose vaccine candidates remains justified.