In response to these variants CDC is now recommending morewidespread use of twomasks, i.e. wearing a clothmask over a disposable mask to reduce tranmissibility. 12 A recent study conducted by the CDC showed that the cumulative exposure of the receiver was reduced 96.4% when both the source of exposure and the person being exposed were wearing a cloth mask over a disposable surgical procedure mask. 13 Although controversial, mask mandates have been associated with a decline in hospitalization rates, presumably through a decline in total number of cases. 14 Similar to masking, use of protective eyewear has also been associated with reduced transmission. 9 Physical distancing, which was implemented early in the pandemic, has been shown to be effective at preventing and delaying spread of the virus and continues to be encouraged. 15 Per guidance from Centers for Disease Control and Prevention (CDC), people should maintain at least 6 feet of distance inside and outside when interacting with others. 12 Large droplets remain the primary source of transmission of this infection and these tend not to travel beyond 6 feet. 16 A recent meta-analysis found that transmission of coronaviruses was lower with physical distancing at lengths of one meter or more, and that protection was increased as distance was lengthened. 9 Ventilation is an additional mitigation strategy advocated for by the CDC based on the idea that ventilation that can help reduce the concentration of virus particles in the air. 17 Improvements to increase ventilation include such recommendations as opening windows and doors (when safe and weather-permitting), evaluating ventilation systems to ensure they are operating properly, reviewing the positioning of supply and exhaust air diffusers and/ or dampers, and improving central air filtration, among others. 17 Fomite transmission remains a theoretical concern, as SARS-CoV-2 has been shown to remain viable on plastic and stainless steel for up to 72 hours. 18 However, spread from touching surfaces has not been frequently observed and is thus not thought to be a common way that the virus spreads. 19 The CDC continues to recommend frequent hand washing or using a hand sanitizer with at least 60% alcohol and disinfection of frequently used surfaces. 19
The Pfizer-BioNTech BNT162b2 vaccine was evaluated in a randomized placebo-controlled trial with 43,448 participants (21,720 vaccine recipients and 21,728 placebo recipients). 20 All participants were 16 years of age or older assigned in a 1:1 ratio to receive two doses, 21 days apart, of either vaccine or placebo. Eight cases of Covid-19 at least 7 days after the second dose were observed among vaccine recipients and 162 were observed among placebo recipients, corresponding to 95% vaccine efficacy. 20 The safety profile of the vaccine was favorable and adverse events mostly consisted of mild to moderate reactions at site of injection that resolved within 1-2 days. Four related serious adverse events were reported in vaccine recipients, and no deaths were considered related to the vaccine. The Moderna mRNA-1273 vaccine was evaluated in a randomized, observer-blinded, placebo-controlled trial conducted in 99 centers across the United States. The study assigned individuals at high risk for SARS-CoV-2 infection or its complications to receive two intramuscular injections of mRNA-1273 or placebo, withdoses separatedby 28days. The primary end point was prevention of Covid-19 illness (onset at least 14 days following the second dose) in participants who had not previously been infected with SARS-CoV-2. The study enrolled 30,420 participants, 15,210 participants in each arm. Symptomatic Covid-19 was confirmed in 196 participants, 185 in the placebo group and 11 participants in the vaccine group, yielding an efficacy of 94.1%. Safety profile was favorable with headache, fatigue and mild to moderate reaction at the injection site most commonly reported. 21 Other notable vaccine initiatives that have undergone phase 3 trials but do not yet hold an emergency use authorization (EUA) include the Astra-Zeneca, Johnson & Johnson (Janssen) and Novovax vaccines. 22
The University of Oxford/AstraZeneca AZD1222 (ChAdOx1 nCoV-19) vaccine has been shown to be efficacious and safe. 23 The vaccine is a two-dose regimen of chimpanzee adenovirus-vectored vaccine that expresses the full spike protein. Results from four ongoing blinded, randomized, controlled trials were pooled for an interim analysis; two of four ongoing trials reported on efficacy and all four reported on safety. Participants greater than or equal to 18 years were randomly assigned 1:1 to the vaccine or control with meningococcal group A, C, W, and Y conjugate vaccine or saline. Two vaccine doses containing 5 × 10 10 viral particles (standard dose; SD/SD cohort) were administered; a subset in the UK trial inadvertently received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). 24 The primary efficacy analysis included 11,636 participants and as primary endpoint evaluated for symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test (NAAT)-positive swab 17
VACCINES
Several vaccines have been developed globally and gained emergency authorization. The two that are currently part of the vaccination campaign in the United States are the Pfizer-BioNTech BNT162b2 and the Moderna mRNA-1273 vaccines. 20,21 Both are lipid-nanoparticle packaged mRNA vaccines that encode a prefusion stabilized SARS-CoV-2 full- length spike protein.
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