THE Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is the causative virus for the disease better known as COVID-19. It belongs broadly to a class of viruses known as coronaviruses, and people are more familiar with the previous SARS and MARS outbreaks. None of these ever got to the scale of the current COVID-19 pandemic.
By Dr Grant Murewanhema
Viruses, such as SARS-CoV-2, which spread rapidly, also multiply very rapidly in a process called replication, where copies of similar virions continue to be made. Now, as you will be familiar with, or at least expect, processes which occur rapidly without efficient control mechanisms are error prone, and this applies to SARS-CoV-2 replication. The errors in replication lead to structural changes in the components of the virus, and this is called mutation.
Mutations can result in minor and inconsequential alterations to the structure of the virus, or can lead to massive changes in the structure of the virus. We are familiar with influenza viruses that periodically undergo processes known as antigenic shift and antigenic drift.
Antigenic drift leads to minor changes in the structure of the influenza viruses, and the pathogenic potential does not change much, and the same vaccines remains efficacious. Sometimes the influenza viruses undergoes antigenic shift, which is a major structural change, producing an almost different virus with different pathogenic potential, and rendering existing vaccines useless against the new variants. Scientists have remained busy with altering influenza vaccines over time, and people have had to receive different jabs over time to cater for the changes and keep the immune system prepared.
It’s not surprising therefore that the SARS-CoV-2 viruses have also been undergoing frequent mutations globally. A lot of the mutations have been inconsequential; however, some have given rise to variants of concern. The two particular variants of concern people have been familiar with include the so-called South African variant, and more recently, the so-called Indian variant, and of course there are others. Just over 18 months since discovery, so much is still to be discovered about SARS-CoV-2, and even newer are the vaccines, with the earliest having been used in the population for about 6 months or so.
The vaccines in use include the mRNA vaccines such as the Pfizer, which are relatively novel, the inactivated virions such as Sinopharm and Sinovac, chemically inactivated through an alcohol-based compound and the viral-vector based vaccines carried on a non-pathogenic adenovirus vector. Fears are that major mutations could potentially render most of the vaccines useless against mutant strains, and pose major blows to COVID-19 pandemic control strategies. Interestingly, the Burnet Institute in Australia is working on coming up with universal SARS-CoV-2 vaccines that will be efficacious against all strains. It remains to be seen how far they can go with this exciting science.
People often ask why there is so much hype about vaccines. Vaccines are known to be the best non-user dependent primary prevention strategy for rapidly spreading infectious diseases, and significant strides have been made in control since discoveries by Edward Jenner over a century ago. Smallpox has been eradicated, polio is near eradication, and mortality from tuberculosis and measles has been significantly reduced, whilst complications from rubella have also been remarkably reduced. We are also excited that we now have effective vaccines against Human Papilloma Virus which causes cervical cancer, and we are hopeful that we will significantly reduce the incidence of this cancer that kills many women in Sub-Saharan Africa over the years.
Of course, due to its elusive nature, the search for an efficacious HIV vaccine has been challenging over the years, though significant progress has been made and important insights have been gained. Vaccination against SARS-CoV-2 has the potential to reduce new infections, reduce disease severity and reduce mortality from severe COVID-19.
The population worldwide should therefore be vaccinated to achieve adequate control of the pandemic. Unfortunately, the vaccination roll-out globally still faces several challenges and is not yet a perfect programme, and also faces serious vaccination hesitancy in other parts of the world, such as in Zimbabwe. Not only are we faced with vaccination hesitancy, but supply chain challenges, unequitable distribution of vaccines, and nationalisation by powerful nations. At the rate at which countries such as Zimbabwe are vaccinating, it may take several years before we reach sufficient levels to attain herd immunity. To date, Zimbabwe has vaccinated just over 600000, which falls far off the target of 60% of the population.
Like in the control of HIV, we have to use a combination of biomedical interventions available to achieve COVID-19 pandemic control, as none of the available strategies is hundred percent efficient and we have not yet vaccinated adequately. Regardless of the variants, the mode of transmission of SARS-CoV-2 remains the same, and therefore our strategies to prevent new infections and break the chains of transmission remain the same. Measures that we have been practising, such as physical distancing, wearing of facemasks, appropriate hand hygiene and avoiding overcrowding and unnecessary travels remain effective. Our people have a tendency to move about even when not necessary, of course taking after those who lead us.
The variants do not move by themselves, but they are moved by people. It remains absolutely necessary to test all returning residents, or visitors to Zimbabwe, and to put them in isolation or contact as necessary. A piecemeal approach where other people are seen as superior and allowed to break protocol only serves as a recipe for disaster. We also need to continue appropriately tracing contacts of confirmed cases, and quarantining them appropriately. Active surveillance countrywide remains an indispensable aspect of COVID-19 pandemic control.
The government and the people should drop the current relaxed mode, and go into full scale active prevention. With our resource limitations, prevention remains the best tool available to us. Zimbabwe is not able to cope with large scale outbreaks of an infectious disease outbreaks, as our public health sector is faced with several other challenges. The disaster that happened between December and February are a clear attestation to our capacity limitation, and the responsibility lies within our capable hands to avoid such similar situations in the future.
(Dr Grant Murewanhema is an epidemiologist, public and global health practitioner and Registrar in Obstetrics and Gynaecology who writes in his own personal capacity. All opinions expressed in the article are independent)