The highly infectious delta variant (or B.1.617.2) of SARS-CoV-2 is fast replacing the alpha variant to become the most prevalent strain globally. It has now spread to more than 120 countries, according to the World Health Organization (WHO). The delta variant was also the dominant strain in the second wave in India, which was bigger and proved to be more deadly than the first wave. The sudden sharp spike in the number of cases overwhelmed the health care system in the country. The exponential r...
To read the complete article
create a free
to instantly read 30000+ free Articles & 1000+ Case Studies
The highly infectious delta variant (or B.1.617.2) of SARS-CoV-2 is fast replacing the alpha variant to become the most prevalent strain globally. It has now spread to more than 120 countries, according to the World Health Organization (WHO). The delta variant was also the dominant strain in the second wave in India, which was bigger and proved to be more deadly than the first wave. The sudden sharp spike in the number of cases overwhelmed the health care system in the country. The exponential rise in cases has been attributed to the highly transmissible nature of the delta variant. The second wave is now receding and the decline has almost been as fast as the surge.
The delta variant is the most transmissible amongst the present four variants of concern. It is around 60% more transmissible than the alpha variant (B.1.117) and causes more severe disease. Sounding a note of caution, the WHO has said “The highly contagious delta variant is the fastest and fittest coronavirus strain that will “pick off” the most vulnerable people. Delta has the potential “to be more lethal because it’s more efficient in the way it transmits between human.”
A recent study attempted to characterize the virological profile of the delta variant and to decode the reasons for its rapid spread. Researchers at the Guangdong Provincial Center for Disease Control and Prevention in Guangzhou, China tracked 62 people who were quarantined after exposure to Covid-19. The viral load was also tested daily all through the course of infection to assess how it changed over time. This data was then compared with data from infections with the original SARS-CoV-2 strain (19A/19B) in 2020.
The results, published as a preprint (medRxiv) on July 12, 2021, showed that the number of virus particles was significant more in persons infected with the delta variant compared to those infected with the original coronavirus strain causing easy spread of the virus. People infected with the delta variant had ~1000 times viral load higher on the day they were firstly detected than in persons with the earlier 19A/19B strain infections; 80.65% samples from delta variant infections contained >6x105 copies/mL in oropharyngeal swabs when viruses were firstly detected compared to the 19.05% samples in 19A/19B infections.
The viral load in delta variant cases was 1260 times higher (Ct value 24) compared to the original 19A/19B strain infections (Ct value 34).
Another notable observation of the study was that persons with the delta variant tested positive for the virus in just 4 days after exposure, while this duration was 6 days for the original virus strain suggesting rapid replication of the delta variant in the respiratory tract. Persons infected with the delta variant therefore are also likely to become infectious much earlier in the disease.
The high viral load and the shorter incubation period, as observed in this study, provide a likely explanation of the high transmissibility and the highly contagious nature of the delta variant early on in the infection.
These findings also have public health implications. Since the number of virus particles in the respiratory tract is high in delta variant infections, the infected persons could spread the infection to larger number of people, in large gatherings, turning it into a superspreader event.
The study also highlights the fact that people suspected to have Covid-19 and their close contacts should be quarantined in a timely manner, before they become symptomatic or test positive on RT PCR, to prevent spread of the virus in the community. The faster people get vaccinated, the sooner we can contain the pandemic.
The need to continue to adhere to covid-appropriate behavior, despite vaccination, cannot be emphasised enough. Wearing a three-layer mask (double masking when in public), physical distancing, hand washing, avoiding crowded places and gatherings are critical to preventing the third wave that is looming just ahead.