COVID-19: Convalescent Plasma and Masks (6 April 2020)

In my three prior coronavirus disease (COVID-19)-related posts, I gave a general overview of coronaviruses, including SARS-CoV-2, the virus that causes COVID-19 (1 and 13 March 2020), as well as a review of investigational therapeutics and vaccines currently being studied (23 March). In this post, I describe another therapeutic approach being explored — the use of convalescent plasma. I also briefly discuss the role of masks in providing protection from COVID-19.

In my 23 March post, I described several investigational therapeutics being used for the treatment of patients with COVID-19, including the antiviral drug remdesivir, the biologic tocilizumab (which has traditionally been used for the treatment of patients with arthritis and other autoimmune conditions), and also chloroquine and its metabolite hydroxychloroquine (which are similarly used for the treatment of patients with certain autoimmune disorders as well as patients with malaria, and may be used alone or in combination with azithromycin for the treatment of patients with COVID-19). An additional therapeutic approach being employed is the use of serum or plasma (the antibody-containing portion of blood) from patients previously infected with the SARS-CoV-2 virus. In contrast to using a vaccine to induce immunity (a process referred to as “active” immunization), this process (referred to as “passive” immunization) instead uses pooled serum or plasma, containing antibodies from convalescent (i.e. recovered) patients, as a therapeutic. There is a long precedent for the use of so-called “immune globulin”, either administered alone as prophylaxis before particular vaccines were available (e.g. hepatitis A and B) or used concurrently with vaccines to confer protection until the vaccine induces immunity (e.g. rabies and tetanus). More recently, convalescent serum has been used as a therapeutic in patients infected with the Ebola virus. Although protection is quick, there are a number of disadvantages to this approach, including the need for pooled serum from a large number of donors, and the risk of serum sickness (a hypersensitivity reaction that usually occurs when the serum comes from an infected non-human animal). Perhaps the greatest disadvantage of passive immunization is that protection is temporary, waning as the antibodies are cleared from circulation (For example, the protection conferred by preformed maternal antibodies disappears after the first six months of a child’s life). As for the role of immune globulin in treating patients with COVID-19, there are several researchers who are looking at this, to include Arturo Casadevall at Johns Hopkins University, as well as researchers at Takeda Pharmaceuticals, who have begun collecting plasma from convalescent COVID-19 patients. (For more on this, see: https://www.takeda.com/.../takeda-initiates-development.../). Presently, convalescent plasma is permitted by the Food and Drug Administration (FDA) for “compassionate use” by means of an emergency Investigational New Drug authorization, which allows physicians to prescribe therapeutics that are otherwise unauthorized. Although currently approved on a case-by-case basis, convalescent plasma is likely to become more available to physicians through expanded access approval from the FDA.

Switching topics, I would like to comment on the use of masks for protection against COVID-19. Although the wearing of masks to protect against allergens and pathogens has long been commonplace in Asia, it has not generally been common practice in western countries until recently. However, amidst concerns for COVID-19, it is increasingly normal to see people in public wearing all manner of masks — some commercially produced, some homemade. At this time, the Centers for Disease Control and Prevention (CDC) simply recommends that individuals wear some type of cloth face covering whenever they are in a community setting. It is important to note that this is meant to be an adjunct to and not a substitute for social distancing. Moreover, recognizing that individuals infected with SARS-CoV-2 may shed the virus during the incubation period (i.e. before they have symptoms), the CDC recommends face coverings in order to protect others from the wearer. However, such face coverings offer little protection to the wearer. At this time, the CDC is not recommending that healthy people wear surgical masks or N-95 respirators, as they are in limited supply and are needed by health care workers and others who are at significantly increased risk of exposure to SARS-CoV-2. Should an individual decide to wear a mask in public, he/she should understand the differences between mask types including their intended purpose, filtration ability, limitations, and appropriateness for extended wear.

The two most commonly used medical masks are the N95 respirator and the surgical mask. The N95 is a tight-fitting mask that filters out most airborne particles including viruses, and when properly fitted, permits minimal leakage around the edges. The N95 is designed to protect the wearer, and although it may be used for extended periods (e.g. per shift), its protective benefit diminishes with each use. In contrast, surgical masks are loose-fitting, leak, and do not reliably protect the wearer from airborne particles such as viruses. Simply put, surgical masks were designed to simultaneously protect the wearer from splashes and sprays of body fluids and to prevent bacteria from wafting from the surgeon’s nostrils into the open wound bed; they were not designed to protect the surgeon from aerosolized viruses.

Even less effective than surgical masks are most homemade masks, which generally confer little or no protection to the wearer. Two published studies on the subject showed that homemade masks, while better than nothing, afford little protection for the wearer against viruses in droplets and aerosols [Disaster Medicine and Public Health Preparedness, Volume 7, Issue 4 August 2013, pp. 413–418 and PLoS One. 2008; 3(7): e2618] Again, the greatest benefit of such masks is protecting others from a wearer who may be shedding virus. Nonetheless, wearing a homemade or purchased mask may serve to remind the wearer to avoid touching his/her face.

As with my previous posts, my intent here is neither to trivialize the pandemic nor to discourage the reader, but simply to inform and, whenever possible, to assuage anxiety. At this point in time, most people with COVID-19 will not require hospitalization and will indeed recover. Antibodies do appear to be protective — something that is relevant to both the natural course of the pandemic and also to the likelihood of creating an effective vaccine; and advances are being made in the creation of diagnostics, therapeutics, and vaccines. In the meantime, our best defense remains social distancing, hand and respiratory hygiene, and a shared sense of civic responsibility.

Until my next update, regards.

Michael Zapor, MD, PhD, CTropMed, FACP, FIDSA
(6 April 2020)