A global pandemic was declared by the World Health Organisation on 11 March 2020, only to be followed by the prolific and uncontrolled spread of both information and misinformation about Covid-19. This data explosion is probably best referred to as an “infodemic” and has led to widespread confusion and anxiety. What follows is an attempt to summarise what is already widely known in scientific circles about this new virus, with the hope of making matters clearer for the reader.
Covid-19 is an abbreviation for Coronavirus Disease-19, which is caused by the new (or novel) coronavirus, SARS-CoV-2. The prefix “corona” comes from the spiky appearance of the virus under the electronic microscope, which bears a fanciful resemblance to a crown, the Greek word for which is “corona”. Each viral particle consists of a core made up of a single strand of RNA (ribonucleic acid). This core is surrounded by an “envelope” which bears the characteristic spike proteins on its surface . Spontaneous and random changes in viral genes that encode for these spike proteins have led to the emergence of mutants and variants, most recently reported from the UK, South Africa, and Brazil.
The virus is transmitted both through the air and by direct contact. Airborne transmission may involve either small droplets (aerosols) or larger droplets (5 microns or greater in diameter). These droplets are typically generated by heavy breathing, coughing, sneezing, speaking, or singing and can travel some distance through the air. On the other hand, contact transmission requires direct contact with either an infected person or a contaminated inanimate surface, such as a table or handrail. The R (reproduction) number reflects the contagiousness or rate of transmission of the virus within a community,, being the average number of infections that a single infected person is potentially responsible for.
Airborne spread can be minimised by face protection and by social distancing (maintaining a suitable physical distance between people). Contact spread can be prevented by diligent hand hygiene, in the form of frequent hand washing and disinfection, and by avoiding hand-to-hand contact. Some particularly contagious individuals and some inconsiderate group events carry an increased risk of virus transmission, and are thus referred to as “super-spreaders”.
Lockdowns, or temporary restrictions in movement and activity, which may include confinement to one’s home in the form of stay-at-home orders, aim to interrupt the chain of community transmission of virus by a process sometimes referred to as “circuit breaking”. During lockdowns, “support bubbles” may provide a safety net for vulnerable people by bringing together selected groups of people who may then safely mingle with one another. Preventing the spread of virus in healthcare settings requires the use of a full set of personal protective equipment (PPE), including face masks or respirators, head covering, goggles, face shields, gowns, gloves and boots. All forms of personal protection must adequately protect the nose, mouth, eyes, hands and feet.
The effects of coronavirus infection vary from person to person. Some infected people may display no symptoms, either because they are pre-symptomatic and due to develop symptoms over the next 2-14 days (the incubation period of the illness), or truly asymptomatic, and will never suffer any symptoms at all. Asymptomatic “carriers” may, however, unknowingly continue to infect others. The typical symptoms of Covid-19 are a high temperature, a new and persistent cough, and loss or change to smell or taste. Shortness of breath is another important presenting complaint. These symptoms are both commoner and more severe in some “at risk” groups of people. Those at increased risk include older people, the obese, people with underlying long-term disease conditions, people with suppressed immune systems, and those from black, Asian and minority ethnic (BAME) backgrounds. “Shielding” is recommended for high- risk people as part of lockdown restrictions. It is important to remember that no single group of people is immune from infection, with cases, and even deaths, having been reported in infants, children, and young, previously healthy, adults.
Antigen tests and antibody tests are used for diagnostic purposes. Antigen tests (polymerase chain reaction or PCR tests) indicate current and active infection, and are usually performed on nose and throat swabs. Antibody tests on blood samples confirm past exposure to, and infection with, the virus. Rapid antigen tests, using newer but less sensitive technologies, have been introduced in order to reduce test turn-around times, providing results within 30 minutes . Antigen tests are usually performed on people with symptoms suggesting Covid-19 and on those in contact with people testing positive for the coronavirus (contact testing), as exemplified by “test and trace” initiatives. In some countries, mass testing programmes have included all available adults, irrespective of the presence or absence of symptoms. Covid-19 ” immunity passports” are issued in some instances for those who have demonstrable antibody levels in the bloodstream and may thus be permitted to avoid any existing lockdown restrictions. Finally, it must be recognised that any diagnostic test may, in a small number of instances, be associated with false positive or false negative results.
Immunity to Covid-19 may be acquired by exposure to the virus, or by vaccination, either of which may lead to the production by the body of protective antibodies to the virus. Vaccination may, however, not guarantee immunity, depending on the efficacy of the vaccine being administered. Vaccines currently available in the UK are either synthetic mRNA vaccines (Pfizer-BioNTech, Moderna) or viral vector vaccines (Oxford-AstraZeneca). Whole virus and viral protein subunit vaccines are also being developed elsewhere. Passive and short-lived immunity may be gained by receiving convalescent blood plasma, obtained from recovered patients, which provides preformed antibodies. Herd immunity is achieved when a sufficient number of people, probably at least 70 per cent of the population, within any given community become immune. When it comes to harmful and potentially life-threatening infections such as Covid-19, herd immunity is best achieved by mass vaccination, while for relatively benign infections, such as chickenpox, immunity that is acquired naturally following exposure to the virus is preferable. In the UK, priority lists of target vaccine recipients have been drawn up by the Joint Committee on Vaccination and Immunisation and are being acted upon.
The usual reason for hospitalisation with Covid-19 is respiratory failure-a failure of adequate oxygenation of the blood within the lungs- due to Covid pneumonia. Treatment in hospital is mostly supportive, and may include oxygen therapy, a ventilator to support breathing, and possibly a stay on the intensive care unit. In addition, steroids (dexamethasone) and various antiviral drugs are being used to help eradicate the virus or mitigate its effects, often as part of a controlled clinical trial. Death can be caused by severe respiratory failure, overwhelming inflammation (“cytokine storm”), blood clots in the lungs, or multiple-organ failure. The case fatality rate refers to the proportion of deaths among people with Covid-19, and is a measure of the severity of an outbreak. Apart from those who die, some patients may not recover fully and instead develop so-called Long Covid, being left with various ongoing symptoms. The higher than expected death toll from Covid-19 is the single most important reason underpinning the various disruptive public health measures aimed at preventing the spread of the virus across the world.
While we live in a free society and can choose to select our own sources of information without hindrance, information about Covid-19 is best obtained from reliable government sources and from the official public health agencies. There is plenty of controversy, even within scientific circles, to confuse matters further for those as yet unclear about the key issues. Information gained by word-of-mouth or from online social media platforms, radio talk shows and sensational newspaper stories, in particular, can frequently mislead. One must particularly beware of the opinions of “experts” communicating in an independent capacity. You have been warned: “fake news” is all around us! Any unwise choices you make now may yet come back to haunt you at a later date.
Ashis Banerjee