The Omicron variant that caused a huge surge in COVID-19 infections worldwide has been studied in terms of prevalence, infectivity, and virulency. The first study conducted in South Africa showed the low pathogenic nature of the Omicron variant compared to the Delta and original Wuhan variants. The deaths, ICU admissions, length of the hospital stay, and also the need of oxygen support all reduced greatly in Omicron infected patients as compared to the earlier variants. The share of the Omicron variant in Delhi (India) rose rapidly. In two weeks (December 21, 2021-January 3, 2022), the omicron prevalence increased from 38% to 81%. Because of the Omicron variant, in the last week of January 2022, Delhi’s caseload surged nine folds. The cases analysed in Delhi, Mumbai, and throughout India revealed that the number of deaths during the Omicron wave was much lower compared to the Delta and Wuhan variants.

The dynamics of the Omicron variant in India, Mumbai, and Delhi have been studied. The % share of the Omicron variant in overall India rose from 0.35% to 97.12% during the period November 29, 2021, to February 7, 2022. Due to the emergence of the Omicron variant, the daily new infections in India rose from a baseline tally of below 8,000 cases to the highest number of 347,063 cases recorded on January 20, 2022. In Mumbai, the Omicron variant completely replaced the Delta and other lineages as reported on March 3, 2022 genome sequencing report. In Mumbai because of the Omicron variant surge, the new infections rose to 20,971 on January 7, 2022, from a baseline tally of 191 daily cases recorded after receding the second Delta variant wave. In real-time, the vaccine effectiveness among the Indian population during the Omicron variant surge was studied and noticed that the two-dose regimen was 99.3% effective in preventing death. The death rate among the hospitalized patients was reduced by 12% among the vaccinated individuals compared to the unvaccinated ones. During the Omicron variant wave, the average age of the COVID-19 patients shifted by 11 years towards the younger age which was because the vaccination among the younger population was low compared to the elderly population.

The surge of the Omicron variant has been studied in overall India, Delhi and Mumbai. The increase in the percentage share of the Omicron strain in total registered cases resulted in a surge of daily new infections. The pathogenicity of Original, Delta, and Omicron variants has been compared using the data collected at the Max Healthcare network in India. The Omicron wave was the least severe of all three waves. The third Omicron wave did not cause much damage due to hybrid immunity generated in the population as a result of vaccination and previous SARS-CoV-2 infection. The low pathogenic nature of the Omicron virus is also the reason for the less severe illnesses the variant caused. Hospitalization during the Omicron wave was just 10% of the Delta wave. The percentage of patients who needed oxygen support was the least during the Omicron wave (23.4%) followed by the Original (63%) and the Delta variant (74%). The less severe nature of the Omicron wave gave the hope of recovering from the deadly devastating COVID-19 pandemic. The symptoms of “long COVID” patients have been compared during all three waves. Nearly the same number of the patients at 5.3% and 5.16% had health issues during Original and Omicron waves, respectively whereas during the Delta surge 5.9% of patients with “long COVID” had symptoms.

The breakthrough infections (BTI) during the Delta wave in the general population have been investigated. The BTI reported in the city of Gurugram (Haryana, India) in the month of August, September, and October 2021 were studied. The monthly BTI in August, September, and October 2021 were 26%, 41%, and 76%, which caused an increase in the monthly caseload to 167, 150, and 206 cases, respectively. Mostly, the patients who had comorbidities developed BTI. However, the BTI reported in the Delta wave did not cause a surge in new cases. The surge was noticed only after the emergence of the Omicron variant of the SARS- CoV-2 virus. In Gurugram, 78.3% sero prevalence recorded in September 2021 was due to vaccination and higher infection rate of 59,921 monthly cases reported in April 2021.

The vaccine breakthrough infections (BTI) among healthcare workers (HCWs) in various hospital networks in India have been studied. Apollo Hospital, PGIMER, Medanta, Civil Hospital, Park Hospital, Max, Fortis, Narayana, and Maulana Azad hospitals were included in the study. During the Delta variant surge, the BTI were reported in the range of 6-25%. By comparing the BTI rates during the severe Delta variant wave and less severe Original (Wuhan, Alpha, Beta, and Gamma) strain wave, it was worked out that the BTI were more among HCWs who were exposed to high viral load. In the initial days of the pandemic in the first wave when the total active cases were less, the rates of BTI were in the range of 1.6- 2.6%. When the viral load increased in the second deadly Delta wave, the BTI rose to 6-25%. The real-time data collected has established that the vaccination gave a protective shield against the novel coronavirus infection. Though the BTI were reported but the severity of the infection remained mild with a low hospitalisation rate and oxygen support requirement. No BTI infected HCWs succumbed to the SARS-CoV-2 infections.