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COVID-19 CURBSIDE CONSULTS Chao-Ping Wu, MD Fatima Adhi, MD Daniel Culver, DO Department of Pulmonary and Critical Care Department of Pulmonary, Critical Care and Sleep Department of Pulmonary and Critical Care Medicine, Respiratory Institute, Cleveland Clinic, Medicine, Baylor College of Medicine, Houston, TX Medicine, Respiratory Institute, Cleveland Clinic, Cleveland, OH Cleveland, OH Vaccination for COVID-19: Is it important and what should you know about it? Published March 5, 2021 ■ ABSTRACT An effective vaccine is considered the best method to threshold varies by characteristics of the population, achieve herd immunity. As of February 2021, 12 vac- the contagiousness of the disease, and inherent prop- cines were in late-stage clinical trials worldwide, with erties of the infectious agent as well as the strength many more in development. Of those, 8 have received and duration of the exposure. emergency use authorization from at least one country’s For SARS-CoV-2, which causes COVID-19, the governing body. These vaccines use various platforms to basic reproduction number (R0) is estimated to be deliver the vaccines, each with pros and cons. Published between 2 and 3; thus, the herd immunity threshold data show these vaccines are effective in preventing the is between 50% and 70%,1 although this may vary severe symptoms associated with COVID-19 in adults with significantly in different environments and popula- few side effects, but challenges remain with storage and tions.2 As of October 2020, less than 10% of the US delivery and treating virus variants. population had a positive test for antibodies (serop- revalence) to SARS-CoV-2.3 It seems clear that wide- ■ INTRODUCTION spread vaccination is the safest and most efficient way The COVID-19 pandemic has claimed more than to achieve herd immunity. 100 million cases worldwide as of January 2021 with- out signs of abating. With limited effective therapeu- ■ HOW FAST CAN WE GET THERE? tic options and the ever-increasing economic burden, As of February 2021, there were 73 vaccines with large-scale vaccination is the most promising strategy various platforms in clinical trials worldwide.4,5 The to dampen the impact of COVID-19. However, expe- advantages and drawbacks of vaccine platforms are dited development and distribution of an efficacious summarized in Table 1. and safe vaccine has posed unprecedented challenges Under Operation Warp Speed, a US government for scientists and manufacturers. initiative, the otherwise lengthy Food and Drug Administration (FDA) approval process of vaccine ■ IS VACCINATION THE ANSWER development and deployment that usually spans TO HERD IMMUNITY? several years has been substantially compressed with The goal for vaccination against infectious diseases a goal to deliver effective vaccines by early to mid- is to achieve community or herd immunity. When 2021 without compromising safety or quality.6 The enough individuals in a community are immune, the initiative planned to achieve this by funding the most chain of transmission is interrupted, conferring indi- promising vaccine candidates based on prespecified rect protection on those who do not possess immu- criteria and supporting diverse vaccine platforms with nity. The proportion of immune individuals needed in potential for rapid development and manufacturing. each community to achieve this indirect immunity to It also facilitated enrollment into large-scale phase 3 others is called the “herd immunity threshold.” The trials and minimized financial risks for manufacturers. These measures allowed the most promising candidate The statements and opinions expressed in COVID-19 Curbside Consults are vaccines to be manufactured in parallel with vaccine based on experience and the available literature as of the date posted. While development while also establishing plans for vaccine we try to regularly update this content, any offered recommendations can- not be substituted for the clinical judgment of clinicians caring for individual deployment. As for February 2021, 5 of the 6 vaccine patients. candidates under the program had reported interim doi:10.3949/ccjm.88a.ccc076 phase 3 trial data analyses, with promising results. CLEVELAND CLINIC JOURNAL OF MEDICINE 1 Downloaded from www.ccjm.org on September 30, 2021. For personal use only. All other uses require permission. TABLE 1 Available vaccine platforms Pros Cons Approved vaccines in use Whole inactivated Easily manufactured Possible Th2 bias Influenza, rabies, hepatitis A, (killed) virus Strong immune response Requires large quantities of virus injectable polio Mature technique Risk of vaccine-enhanced disease Requires booster shots Live attenuated Entire viral repertoire Risk of reversion/recombination Measles, rubella, mumps, yellow fever virus Very strong cytotoxic response Risk of infection in immunocompro- Mature technique mised patients Requires cold chain distribution Protein subunits Simple to produce Less immunogenic Influenza A strains, hepatitis B, Safe, few side effects Requires adjuvants acellular pertussis Slower manufacture Viral-like protein Safe and stable Enveloped VLP more challenging to HPV, preclinical SARS-CoV-1 Immunogenicity produce DNA Rapid development Potential integration to host genome Not currently licensed Noninfectious Less Immunogenicity Thermostable Delivery challenging; requires cold chain distribution mRNA Rapid development Instability SARS-CoV-2: EUA from FDA Noninfectious, non-integrating Low immunogenicity (Pfizer, Moderna) Delivery challenging; requires cold chain distribution Viral vectors Safe Pre-existing immunity against vector Ebola. SARS-CoV-2: EUA from FDA Durable response (Johnson & Johnson) EUA = emergency use authorization; FDA = Food and Drug Administration; HPV = human papilloma virus; mRNA = messenger ribonucleic acid; SARS-CoV = severe acute respiratory syndrome; Th2 = T helper type-2 cells; VLP = viral-like protein ■ HOW IS THE EFFICACY AND SAFETY Middle East Respiratory Syndrome (MERS-CoV) OF THE VACCINES BEING ENSURED? wherein non-neutralizing antibodies to viral spike protein led to increased inflammation and injury in It is not known whether measurable antibody titers 8 effectively protect against SARS-CoV-2 infection or the liver and lung. Thus far, no such pattern has how long this protection could last. Given the uncer- been identified in the preclinical and clinical studies tainty surrounding the protective effect of antibodies, for SARS-CoV-2. However, it is crucial to monitor the FDA recommends using symptomatic infection in study participants beyond the trials as well as vaccine addition to the confirmation of active SARS-CoV-2 recipients outside the trials to gather long-term safety infection (eg, using reverse transcriptase polymerase data. chain reaction testing) as the key endpoint for study- The US Department of Health and Human Ser- ing the efficacy of vaccine candidates. The efficacy vices has established robust follow-up procedures for endpoint point estimate recommended by the FDA gathering that data. It includes passive surveillance to establish efficacy is at least 50% versus the control through its Vaccine Adverse Event Reporting System group in clinical trials.7 As of February 2021, safety (VAERS) program that relies on the public or manu- data in children and pregnant women were lacking, facturers to report any adverse effects. Active surveil- and further investigation is urgently needed. lance of vaccine safety is provided by Vaccine Safety In addition, concern has been raised regarding a Datalink, a collaborative network that uses electronic theoretical risk of vaccine-enhanced disease similar health record data from several sites to monitor vac- to that seen in animal studies of SARS-CoV and the cine safety in near real-time. In addition, the V-safe smartphone-based app uses text messages to conduct 2 CLEVELAND CLINIC JOURNAL OF MEDICINE Downloaded from www.ccjm.org on September 30, 2021. For personal use only. All other uses require permission. frequent health check-ups on vaccine recipients who CoV-2 S protein is wrapped in lipid nanoparticle for- have registered for the program. mulations to ensure its delivery to the cells without RNA degradation in the circulation. This piece of ■ CAN A VACCINE BE USED BEFORE BEING mRNA, by itself, is incapable of causing disease and is APPROVED FOR USE? degraded within the cell without entering the nucleus Under its Emergency Use Authorization (EUA) pro- and thus, does not interact with human DNA. To gram, the FDA can facilitate the use of medical prod- increase the immunogenicity, the genetic sequence ucts that have not been granted formal approval by is modified, so that the resultant protein is locked temporarily allowing their use during a public health in its prefusion conformation (the shape it naturally emergency. The EUA process is conducted without takes just before the virus fuses with the human cell sacrificing scientific standards of integrity or safety. membrane). For the COVID-19 vaccines, the EUA designation is BioNTech-Pfizer BNT162b2 based on a thorough review of the efficacy and safety This vaccine received FDA EUA on December 11, data by both the FDA Vaccines and Related Biologi- 2020, based on preliminary data from an ongoing cal Products Advisory Committee and the Centers multinational, randomized, observer-blinded phase for Disease Control (CDC) Advisory Committee on 3 trial.10 The World Health Organization (WHO) Immunization Practices, which independently pub- assigned it emergency use listing on