The new coronavirus, Covid-19, has gone on the warpath. Accordingly, some leaders have also placed their nations on a war footing. Matt Hancock, Secretary of State for Health, thus stated in the House of Commons, on 16 March 2020, that “We are in a war against an invisible killer and we have got to do everything we can to stop it”. On the same day, French President Emmanuel Macron described the enemy as “invisible, elusive, but it is making progress”. The next day, an increasingly Churchillian Prime Minister, Boris Johnson, went on to make a timely reference to a “wartime government”. Similar rhetoric is increasingly to be heard across the globe at the time of writing.
Military success depends on recognising, protecting against, containing and eventually neutralising the enemy. A better understanding of the enemy is essential to victory. At this crucial time, it is thus relevant to examine some of the key terms and concepts pertinent to the present Covid-19 pandemic. My report is based on a search of official sources of health information and is constrained by a paucity of “evidence-based” and peer-reviewed publications on the matter.
A virus is a tiny particle, visible only under an electron microscope. It is made up of a nucleic acid core, or genome (either DNA or RNA), hidden inside a protein shell, or capsid. Some viruses also have an additional protective fatty (lipid) envelope. A virus can survive on its own for only a short period of time, depending on help from other living cells in order to multiply and then propagate. Invading a host cell is absolutely necessary for viruses intending to make their mark on the wider world.
Coronaviruses are a group (“family”) of enveloped RNA viruses, which have been around for a while, first discovered in the late 1960s. Their name comes from a fanciful resemblance to a spiky crown (corona) when seen under the microscope. Coronaviruses mostly live in animal hosts, known as reservoirs. Humans tend to pick up coronaviruses accidentally, through contact with infected animals (domestic or peri-domestic) in the first instance. These so-called intermediate hosts transfer infection from animal reservoirs to humans, often acting as “amplification vectors” in the process.
Coronaviruses have been known to cause severe respiratory illnesses, such as SARS (severe acute respiratory distress syndrome) in 2003 and MERS (Middle Eastern respiratory syndrome) in 2012, in addition to commoner and less severe conditions such as the common cold. Bats were recognised to be the reservoir for SARS and MERS, with civet cats and dromedary camels serving as intermediate hosts.
The newest coronavirus, Covid-19, was first recognised in the Chinese city of Wuhan in December 2019, and probably originated in infected bats. The virus has since rapidly travelled globally, transmitted from human-to-human. Covid-19 causes a respiratory illness, and is found in respiratory secretions. Secretions are transmitted either as airborne aerosolised droplets, as in sneezing or coughing, or by being deposited on various surfaces (glass, metal, plastic) and then conveyed by hands to other hands or one’s own face. Transmission of these droplets can be minimised by “cough etiquette” and also by social distancing. The WHO thus recommends a distance of at least one metre between people interacting socially. In the UK, members of the public should stay at least two metres apart. Properly measured and fitted face masks, used properly, should be used by those working with, and caring for, people infected with Covid-19 but do not protect uninfected people merely walking about in the streets, even in so-called “hot spots” of infection. Contact transmission of infected secretions can be avoided by frequent and diligent hand washing with soap and water. Covid-19 can reportedly survive on various contaminated surfaces, that have not been properly disinfected, for at least 48 to 72 hours, although some suggest this period may be as long as nine or ten days.
The incubation period refers to the time between exposure to the virus and the appearance of symptoms, which seems to range between two to fourteen days, with a median of five days. This time period provides the rationale for the usual recommended period of self-isolation. The period of infectivity, during which people actively ‘shed’ the virus and can infect others, seems to reach a peak within the first seven days of symptoms.
People infected with Covid-19 display a spectrum of symptoms. They may either have no symptoms at all and look well, or only develop mild symptoms. At worst, severe respiratory symptoms can lead to respiratory failure and even death. Infection can be transmitted by those without any symptoms, so-called “carriers”. The risk of severe illness seems to be higher in “older” people and those with compromised immune systems and certain types of chronic illness. The risk to pregnant women is, as yet, unknown, but avoiding any potential exposure to Covid-19 infection is being recommended at present. Luckily, children seem less prone to develop severe illness.
Symptoms which suggest Covid-19 include fever, a new and persistent cough, and shortness of breath. In the UK, people are currently undergoing remote triage of their symptoms, phoning up 111 in the first instance for advice. These symptoms are, however, not specific to Covid-19 and can also be caused by many other illnesses. Deciding on whether someone may or may not be suffering from Covid-19 infection is thus frequently nothing more than educated guesswork, guided by a simple algorithm.
Covid-19 infection is confirmed by laboratory testing. Currently, in the UK, such diagnostic testing is mostly confined to those admitted to hospital with symptoms that may be due to Covid-19. Community testing is not available at present. Those with mild symptoms, or those who have been in recent contact with infected people or those likely to be infected, are being advised social isolation at home, without recourse to testing. The scope and scale of testing seems to vary widely between countries, guided by different national strategies for epidemic control. Newer approaches to mass testing within the community even include such innovations as drive-through testing.
The diagnostic test is known as the reverse transcriptase-polymerase chain reaction. As Covid-19 is a respiratory illness, nasal swabs, throat swabs, or sputum specimens are used to provide samples for testing. Blood or urine tests are not performed, as Covid-19 does not appear to be a viraemic illness, associated with circulating viruses in the bloodstream. In the UK, testing is being performed in laboratories specifically designated for the purpose by Public Health England. The result is expected to be made available within 24 hours of testing, but is frequently delayed for a variety of reasons.
The death rate for Covid-19 seems to differ from country to country, ranging between 1 per cent and 3.4 per cent of those infected. Survivors of Covid-19 infection are expected to develop lifelong immunity, although people with “recurrent infection” have been identified. It remains unclear whether this represents genuine reinfection or merely reactivation of already established, and yet dormant, infection.
So-called “herd immunity” can protect people, provided that at least 60 per cent, more usually 80 per cent, of the community are already immune, either previously infected or vaccinated. Covid-19 is, however, a new infection. Not only is there no herd immunity within the community, but a vaccine has yet to be developed. There is thus an understandable desire to fast-track a Covid-19 vaccine, given the global impact of the pandemic. Accordingly, phase 1 human safety trials have commenced in the US. A vaccine needs to be both safe as well as effective, hence necessitating further phase 2 efficacy trials. Vaccinologists generally cite a period of 12 to 18 months as the bare minimum before any new vaccine can be approved for unrestricted public use.
A steady stream of reports about the Covid-19 pandemic is rapidly turning into an unmanageable information overload, a sea in which it is easy to drown. A “viral” spread of misinformation within social media communities is, in particular, causing widespread confusion and anxiety. Hopefully, most people will prefer to be guided by authoritative bodies, such as the WHO (World Health Organisation), the NHS Coronavirus website, and the CDC (Centers for Disease Control), at a time when our knowledge continues to evolve at a rapid and frequently dizzying and disorienting pace.
Ashis Banerjee (retired consultant in emergency medicine)
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