Afra Shamnath / Vinod Scaria
09-08-2021
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- A Malayalam version of this article is available à´•ോà´µിà´¡് -19 à´µാà´•്à´¸ിà´¨ുà´•à´³ും à´¬്à´°േà´•്à´•്à´¤്à´°ൂ à´°ോà´—à´ª്പകർച്à´šà´¯ും – നമ്മൾ ആശങ്à´•à´ª്à´ªെà´Ÿേà´£്à´Ÿà´¤ുà´£്à´Ÿോ ?
Unprecedented advances in science which has enabled the development of a number of COVID-19 vaccines within a very short span of time. Many of these vaccines are now approved by national and international regulatory agencies for widespread use in populations. Currently two types of vaccines are approved and widely used in India. This includes the adenovirus vector vaccine - AstraZenaca / Covishield and the whole virion vaccine - Covaxin. Another adenovirus vector vaccine Sputnik has also been approved for use in India recently. Apart from these a number of vaccines including a DNA vaccine and mRNA vaccines are currently under development and/or awaiting approvals for use in India.
Vaccine breakthrough infections are defined as infections in fully immunised individuals.For COVID-19, a person is considered fully immunised when the person covers 2 weeks after the 2nd dose of the vaccines currently available in India. No process of immunisation is 100% effective. Therefore breakthrough infections are expected in a small proportion of individuals as we immunise a large proportion of our population. Early estimates for the estimates of breakthrough infections for the different vaccines have come from the Phase III clinical data for the vaccines. For the vaccines currently approved in India and widely used, the estimates from different studies range from 0.2% to 0.77% (Ella et al. 2021; Voysey et al. 2021)
Does that mean the COVID-19 vaccines are ineffective ?
The vaccines available in India have been extensively studied with respect to the safety and efficacy. These vaccines have been consistently shown to prevent severe disease and death through multiple studies in India and abroad.
Should I be worried about breakthrough infections?
Breakthrough infections occur in only a small proportion of vaccinated individuals. A number of reports from India and abroad until date suggest that breakthrough infections result in mostly mild to moderate symptoms pointing out to the fact that vaccines are indeed effective in preventing serious disease and death.
The vaccine is based on the earlier COVID-19 genome. Would I be protected against the newer variants?
Viruses mutate at a constant rate and therefore variants in SARS-CoV-2 are generated as part of the natural process of evolution. The mutations would accumulate as long as we prolong infections in humans. Many of these variants are only dissimilar in a few genetic mutations. This means that it does not entirely change the virus or its properties. It is therefore not anticipated that variants make vaccines completely ineffective. Despite the rise of variants, studies have suggested that effective vaccination can significantly reduce hospitalization and deaths in populations. Recent reports on the vaccines currently being administered in India have shown to be effective against the emerging variants in India including delta (B.1.617.2). When a large number of people are vaccinated in a population, this significantly reduces the infections in the population and therefore the possibility of the virus mutating further.
So should I get the vaccine ?
If you are eligible for a vaccine, you should indeed take up the vaccine and complete the prescribed schedule as soon as possible
It is also important to emphasize that the high-risk individuals especially individuals with comorbidities would significantly benefit from being vaccinated avoiding catastrophic outcomes with COVID-19 infection.
It also needs to be emphasized that while being vaccinated, extreme caution and full observation of public health measures like double masking and physical distancing is important to prevent the infections that might arise by crowding or gathering with people who might be infected.
How can I prevent breakthrough infections?
Breakthrough infections occur in a small subset of individuals who have completed the vaccine schedule. It is therefore important that one completes the vaccine schedule as per the prescribed schedule. By promoting people around you to get vaccinated, you also prevent the possibility of infections and deaths due to COVID-19 around you, and also therefore reducing the possibility of new variants of the virus emerging.
It is also important to ensure that the public health measures are adhered as strictly as possible, even after being vaccinated since these measures along with the immunity provided by the vaccines have a significant impact in curbing the spread of the virus.
One should always keep in mind that new variants arise when infections occur . By vaccinating yourself, you protect yourself and the dear ones around you by reducing the chance of infections and thereby reducing the chance of viruses evolving.
The authors are researchers at the CSIR-IGIB . All opinions expressed are personal and do not reflect the opinion of their employers or organisations associated. The Authors can be reached at @AfraShamnath OR @vinodscaria on Twitter
Viruses, especially betacoronaviruses, do not evolve at a constant rate. It depends on the global viral load, as you note, but more importantly, since betacoronaviruses have their own replication machinery, they can mutate how they mutate: by altering the function of RdRp or ExoN, they can change their evolutionary style regardless of the site substitution rate or, to a degree, cumulative viral load.
ReplyDeleteFor example, nsp14 knockout viruses mutate so rapidly that they can't produce viable progeny.
https://pubmed.ncbi.nlm.nih.gov/32938769/
This section also omits the potentially critical factor of original antigenic sin, which is dreadfully under-researched in the literature. We have seen that the memory B cells produced by vaccination do not exhibit the hypersomatic evolution that those produced by infection do. We don't know how the Tfh cells and germinal centers will work, but we do know antigenic drift is occurring and accelerating as global case loads grow and new variants emerge. Delta had not drifted far enough and will seek to increase its pathogenicity at least to levels associated with Delta in unvaccinated individuals: each sequential major dominant strain has been more deadly than the previous, indicating that virulence is beneficial for transmission for this virus.
Furthermore, vaccination applies direct selective pressure on the virus to escape adaptive immune responses. The more vaccinated people there are, the more pressure there is. High transmissibility among vaccinees is the last thing we want to see, but we're seeing it, with Israel estimating only a 39% efficacy in preventing infections in real-world settings in their last report.
Have you taken the time to ask yourself why no updated vaccines have been released targeted against the epitopes in Beta, Delta, or more relevantly, the most recent descendants of Delta? I find it hard to believe that the rationale is because the existing ones are good enough, given the Provincetown outbreak. It's transmission that causes mutation, not disease.
More time has elapsed since work began on mRNA-1273.351 than it took to get the original mRNA-1273 to market. It's hard for me to not take that as evidence of immunological imprinting making booster and update shots difficult, which could result in challenges in revamping the immune response as this antigenically drifts further.