CME INDIA Presentation by Admin.
Is COVID-19 forever?
Lots of panic-laden news keep appearing. Physicians need to know the realities to counsel the public. We need to know some emerging and known facts and ponder about the unknown facts too.
- Multiple, distinct infection from the same virus species throughout lifetime – A salient feature.
- Reinfection, in which an individual is subjected to multiple, distinct infections from the same virus species throughout their lifetime, is a salient feature of many respiratory viruses.
- We are aware of influenza viruses, respiratory syncytial virus, rhinovirus, and the endemic coronaviruses – which are notoriously known due to their ability to produce repeat infection.
A critical concern
- Whether humans will experience reinfections with COVID-19.
- Will it be endemic?
Immune Escape is Real
- For or many viruses keep these these things in mind when considering reinfection:
- Insufficient adaptive immune response.
- Waning immunity.
- Immune escape.
Evidence with Serological studies
- Most SARS-CoV-2 infections, regardless of severity, induce development of some specific antibodies.
- Whether those antibodies are sufficient to provide long-term effective protection or if other adaptive immune components are present and functional, is not well known with SARS-CoV-2.
- Immune response to SARS-CoV-2 infection is heterogeneous.
- If someone has experienced asymptomatic infections, may get a weaker immune response than those experiencing more severe disease.
- Some individuals never develop sterilizing immunity following infection with SARS-CoV-2.
- May be some need multiple exposures for affinity maturation and development of long-lasting protection.
Time factor and Immune Escape, might be operating
- If the initial adaptive immune response is robust and protective, it may dissipate over time, leaving the host vulnerable to reinfection.
- Immune escape can facilitate reinfection.
- What happens when a virus, during its continued serial passage through a host population, starts point mutations? This is known as antigenic drift.
- Antigenic drift, may lead to conformational changes of viral surface proteins that disrupt the binding of antibodies previously generated against an earlier variant.
Nothing is clear about SARS-CoV-2 virus
- The time scales of waning immunity and immune escape yet to be defined for SARS-CoV-2.
- Mutation rate of the SARS-CoV-2 genome appears to be slower than that of influenza viruses.
- To date, we have some evidence of SARS-CoV-2-specific antibody waning in a longitudinal study. We have also a few verified repeat SARS-CoV-2 infections.
No need to Panic with Reinfection
- Although reinfections can occur, the number of reinfection cases is not currently sufficient to generalize the duration of immunity at population scales or the severity of repeat infection.
- Whether reinfections will be commonplace, how often they will occur, how contagious reinfected individuals will be, and whether the risk of severe clinical outcomes changes with subsequent infection remains to be understood.
- Naturally acquired infections with the four endemic HCoVs (OC43, HKU1, 229E, and NL63) indicate that reinfections with the same HCoV type are common within 1 year.
- Sequential infections with the same influenza virus strain can occur in less than 2 years.
- Longitudinal immune profiles from SARS survivors showed a stronger immune response with neutralizing antibodies persisting for 2 to 5 years.
- To date, responses among the few patients with verified SARS-CoV-2 reinfection have been heterogeneous with one apparent repeat infection requiring hospitalization.
Endemicity, could it be?
- Suppose, reinfection proves commonplace, and a highly effective vaccine is not delivered to all, SARS-CoV-2 will likely become endemic.
- The typical time scale at which individuals experience reinfection is very important with seasonal differences in transmissibility. These will determine the pattern of endemicity.
- Outside the tropics, shorter days and less sunlight exposure may suppress immune function.
- Science has tried to understand the role of temperature, sunlight, humidity, ozone, and pollution SARS-CoV-2 viability and transmissibility. We do not have currently conclusive insights.
- It appears that environmental conditions, such as sunlight and humidity, may modulate SARS-CoV-2 transmissibility. But these are not enough to check transmission during the first waves of the pandemic as immunity is generally low.
Co-infections, how endangering the pandemic?
- To date, some SARS-CoV-2 coinfections have been documented (including coinfections with influenza and RSV.
- Testing for multiple pathogens has not been routinely carried out, and scarce data exists.
- Studies prior to the pandemic indicate that simultaneous infections with multiple respiratory viruses are not uncommon. These are not associated with increased disease severity.
Post Pandemic Modelling Projection
- Duration of immunity and cross-immunity between SARS-CoV-2 and the other beta coronaviruses (OC43 and HKU1) has been projected.
- A duration of immunity similar to that of the other beta coronaviruses (∼40 weeks) could lead to yearly outbreaks of SARS-CoV-2.
- If a longer immunity profile emerges coupled with a small degree of protective cross-immunity from other beta coronaviruses, it will lead to the apparent elimination of the virus but might be followed by resurgence after a few years.
- Other scenarios are possible.
- There are many processes at play.
- Nobody knows what is in the future. We hope that covidology will be a dead science and covidologists will return to their original speciality. This is the best bet ….
CME INDIA Learning Points
- The post pandemic transmission dynamics of SARS-CoV-2 will depend on factors including the degree of seasonal variation in transmission, the duration of immunity, and the degree of cross-immunity between SARS-CoV-2 and other coronaviruses, as well as the intensity and timing of control measures.
- It has been projected that even in the event of apparent elimination, SARS-CoV-2 surveillance should be maintained till 2024-2025.
- SARS-CoV-2 can proliferate at any time of the year.
- If immunity to SARS-CoV-2 is not permanent, it will likely enter into regular circulation.
- Social distancing strategies could reduce the extent of the SARS-CoV-2.
- Highly effective distancing could reduce SARS-CoV-2 incidence enough to make a strategy that is based on contact tracing and quarantine feasible.
CME INDIA Tail Piece
- Will SARS-CoV-2 become endemic? Jeffrey Shaman, Marta Galanti. Science 30 Oct 2020:Vol. 370, Issue 6516, pp. 527-529 DOI: 10.1126/science.abe5960
- Projecting the transmission dynamics of SARS-CoV-2 through the postpandemic period. Stephen M. Kissler et al Science 22 May 2020: Vol. 368, Issue 6493, pp. 860-868 DOI: 10.1126/science.abb5793
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