The coronavirus pandemic has hit in full force and the news keeps evolving. To update our readership, we spoke to Prof. Suranjith Seneviratne, who is a professor and consultant in clinical immunology and allergy at the Institute of Immunity and Transplantation and Health Services Laboratories, London, UK, and Nawaloka Hospital Research and Education Foundation Sri Lanka.
How do new variants such as the Delta variant (or those that will come next) become more infectious or more serious?
We need to look at how new variants arise. Viruses multiply (replicate) and spread from cell to cell and person to person. During this process of multiplication, changes may occur in the genetic make-up of the virus. Some RNA viruses, such as the flu viruses, change more often than others. Many of the changes are not of any consequence, whilst few may have specific and important follow-on clinical effects. The changes may affect one or more of the following: transmission, disease severity, diagnostic testing aspects, the effectiveness of medications, and finally, vaccine effectiveness.
The Delta variant
It was first identified in Maharashtra in late 2020 spread throughout India, displacing the Alpha variant and other pre-existing lineages. It has now spread globally and currently is the predominant variant in the UK, the US, and several countries including Sri Lanka. By the end of July 2021, Delta was the cause of more than 80% of new Covid-19 cases in the US.
Transmission
The Delta variant is 60% more transmissible than the Alpha variant (which is 50% more contagious than the original strain of SARS-CoV-2). The highest spread of the Delta variant with severe illness outcomes has been observed in places with low vaccination rates. Currently, most hospitalisations and almost all deaths are among the unvaccinated. The US Centres for Disease Control and Prevention (CDC) described the Delta variant to be as contagious as chickenpox and more transmissible than the common cold and influenza, as well as the viruses that cause smallpox, MERS, SARS, and Ebola. A recent study also showed that vaccinated people could transmit the Delta variant.
Clinical findings
The Delta variant appears to be causing illness among young adults. In the UK it was found that children and adults under the age of 50 to be 2.5 times more likely to become infected with the Delta variant. In Uganda, 66% of severe illness in people younger than 45 years was attributed to the Delta variant. Some reports from the UK (where more than 90% of the cases are due to the Delta variant) point to differences in symptoms from that seen with the original SARS-CoV-2 virus strain. Cough and loss of smell appear to be less common, and headache, sore throat, runny nose, and fever have also been observed. Some studies suggest the Delta variant may cause more severe disease among unvaccinated persons than previous strains.
Breakthrough cases due to the Delta variant
Fully vaccinated people with Delta variant breakthrough infections have been reported. Such persons have high amounts of virus in their nose and throat and can spread the virus to others, irrespective of them having symptoms or not. Breakthrough infections happen much less often than infections in unvaccinated people. The greatest risk of transmission is among unvaccinated people who are much more likely to contract, and therefore transmit, the virus. Vaccinated people appear to be infectious for a shorter period.
Would a Covid-19 vaccine booster be needed?
Currently, there is intense discussion if a booster vaccine dose (either against the original virus or the Delta variant) would be needed by those who have been fully vaccinated. Very recently, the Food and Drug Administration (FDA) approved the use of the Pfizer and Moderna vaccines as a third dose for certain immuno-compromised persons.
Facemasks
The World Health Organisation (WHO) has encouraged mask-wearing even among vaccinated people. In July 2021, the CDC updated its guidance to recommend that both vaccinated and unvaccinated individuals should wear masks in public indoor settings, in areas of high transmission. Currently, anyone who is unvaccinated and not practising preventive strategies (such as wearing masks and following other social distancing measures) is considered to be at high risk of Delta variant infection.
What are the currently observed effects of Covid in children?
In general, children infected with the SARS-CoV-2 virus develop mild disease symptoms, or are asymptomatic. However, some children may get serious inflammatory complications that may adversely affect their health and well-being. Covid-19 may rarely cause death in children although the rate is much lower than in adults. Some children may get the condition called Long Covid, following a mild SARS-CoV-2 infection. This may have health-impacting effects that could continue for weeks or months beyond an initial mild illness. Recently, in some countries, the number of Covid-19 cases has been higher in younger persons compared to the older population. Children with mild symptoms may spread the virus between themselves and to adults in their family and outside their home. Older children tend to transmit the virus more easily than younger children. Vaccine immunity has become increasingly important with the more transmissible Delta variant.
“Herd immunity against SARS-CoV-2 (either through vaccination or natural infection) is a prerequisite to end this pandemic,” stated Prof. Seneviratne.
Higher transmission rates increase the threshold for reaching herd immunity and vaccinating children and adolescents may be necessary for reaching such a target.
What is Long Covid?
Long Covid is used to describe signs and symptoms that last for longer than four weeks after getting Covid-19. It has been divided into two stages:
- Ongoing symptomatic Covid-19 (with symptoms lasting for four to 12 weeks) and
- Post-Covid-19 syndrome (with symptoms that last for more than 12 weeks and can’t be explained by another diagnosis). Variable symptoms may occur and could be intermittent.
The symptoms include extreme fatigue, problems with memory and concentration (commonly referred to as brain fog), chronic cough, breathlessness, difficulties with sleeping, dizziness, pins and needles, joint pains, chest tightness, heart palpitations, depression and anxiety, tinnitus, earaches, nausea, diarrhoea, abdominal pain, loss of appetite, temperature dysregulation, headaches, a sore throat, changes to the sense of smell or taste, and skin rashes.
What is the basis for the reports of severe infection in those who are vaccinated?
Those who are fully vaccinated against SARS-CoV-2 have high levels of protection against severe infection, hospitalisation, and death due to Covid-19. Breakthrough cases of Covid-19 have been observed among the fully vaccinated (i.e. two weeks after receiving two vaccine doses). However, there is evidence that the vaccines were very good at preventing severe illness. Breakthrough infections tend to be mild or asymptomatic and may go undetected. Thus, it is difficult to know the full extent of the problem.
“Currently, the number of Covid-19 cases and deaths among the fully vaccinated is very small compared to the unvaccinated. However, none of the vaccines are 100% effective at preventing infection; the emergence of new SARS-CoV-2 viral variants, such as the highly transmissible Delta variant, and the waning of long vaccine immunity, can have an impact,” stated Prof. Seneviratne.
The waning of long-term vaccine immunity
Currently, we do not know how long vaccine-induced protective immunity lasts. This aspect would be particularly important among clinically vulnerable individuals and the elderly who were vaccinated early on in the vaccine rollout process. If immunity wanes after a certain period, a booster dose would need to be considered.
The current Covid-19 vaccines are very good at protecting against severe infection, hospitalisation, and death but they are less effective at protecting completely against infection. Fully vaccinated people are much less likely to suffer from a full-blown SARS-CoV-2 infection. An important question is whether breakthrough cases are happening more frequently than we expected. However, with the rising case numbers, it’s prudent to adhere to all health and safety precautions mandated by the Government.
