Delta variant of Covid-19 far more infectious than smallpox

The Delta variant of Covid-19 is far more contagious than smallpox and virulent than other mutations of the virus, says a study recently published by Qatar Medical Journal and featured on QScience. “The R-naught of the original Covid-19 strain found in Wuhan was 2.4-2.6 while that for the Alpha strain was 4-5 and for the Delta strain, it was 5-8. This implies that a person infected with the Delta variant of Covid-19 can transmit the infection to eight people,” it is explained.R-naught is an epidemiological term indicating how contagious an infectious disease is. It is a reproduction number to measure the transmisibility of infectious agents. Mohamed A Hendaus and Fatima A Jomha, the authors of the study ‘Delta variant of Covid-19: A simple explanation’ note that with such high R-naught, the Delta variant could be twice or even more transmissible than original Covid-19 strain.“These data signify that the Delta variant of Covid-19 is more infectious than smallpox, which has an R-naught of 3.5-4.6. Hence, it is crucial for people to comply with physical distancing and other precautionary measures to better take control of the infection caused by the Delta variant,” says the study.The article also suggests that several of these Covid-19 mutations may affect immune responses, especially at the level of antigenic regions of receptor-binding proteins, permitting better attachment to the receptor cells and evading immunity more easily. The article highlights a study in mainland China which identified 167 patients with Delta variant infections. “Data were retrieved from daily, sequential polymerase chain reaction testing of the isolated subjects. The authors showed that the viral load of the first positive test of patients with Delta variant infections was ∼1000 times higher than that of the patients with 19A/19B strain infection, which caused the epidemic in early 2020. This insinuates the impending faster viral replication rate and more infectiousness of the Delta variant in the initial phase of the infection,” it said.Another major point in the article is that vaccine efficacy showed modest differences against the Delta variant and the Alpha variant after the administration of two doses. "However, these differences in vaccine effectiveness were more prominent after the administration of the first dose. A recent study published in the 'New England Journal of Medicine' included a total of 19,109 patients affected by Alpha variant or Delta variant. It demonstrated that the efficacy after one dose of Oxford/AstraZeneca Covid-19 vaccine or Pfizer–BioNTech Covid-19 vaccine was particularly lower in individuals infected with the Delta variant than in those infected with the Alpha variant," said the article.After administering two vaccine doses, the effectiveness of Pfizer vaccine was 93.7% among patients infected with the Alpha variant compared with 88.0% among those infected with the Delta variant.The same study showed that for AstraZeneca vaccine, the efficiency of two doses was 74.5% in individuals infected with the Alpha variant and 67.0% in those infected with the Delta variant. The article also points out that halting the spread at the source remains the key in preventing the spread of the virus as well as preventing new variants of the virus. "Regularly used precautions employed since the beginning of the pandemic should be strictly followed. These measures include physical distancing, avoiding closed places or crowds, wearing a face mask or face shield, and cleaning hands frequently. By reducing the amount of viral transmisibility, the odds of a new variant emerging are low. Making the Covid-19 vaccine available globally is crucial in ensuring herd immunity,” it concluded.