Two doses of Covishield gives 94% protection against ICU admission and 77% protection against hospitalisation, says a new study carried out on more than 10,000 healthcare workers at Christian Medical College Vellore.
There is, however, no head-to-head comparison with Covaxin because too few individuals received the homegrown vaccine.
No deaths have been seen in vaccinated healthcare workers but one demise was reported in the unvaccinated group. The only staff member who died since the beginning of the pandemic had multiple co-morbidities and had not taken the vaccine, said the study.
The research paper has been released on a preprint server and is yet to be peer-reviewed.
Among 7,080 healthcare workers who completed two weeks after two shots, the vaccine protects 77% of them from hospitalisation, 92% from requiring oxygen and 94% from hospital admission. The protective effect of vaccination in preventing infection was 65%.
Even with a single shot the protection against hospitalisation, oxygen therapy and ICU admission was 70%, 94% and 95% respectively. The protective effect to prevent the Covid-19 infection was 60% with a single shot.
“Vaccines are working well! They are good against infection and great against severe disease. Here is the first data from healthcare workers at CMC Vellore,” tweeted Gagandeep Kang, India’s foremost vaccine expert and a professor at CMC, who is not associated with the study.
The hospital vaccinated 8,991 staff (84.8%) between January 21 and April 30. 2021. A majority (93.4%) received Covishield while the rest got Covaxin. Some of them got only one shot so far because of the increased spacing between the two doses of Covishield.
Subsequently, the CMC researchers analysed incidences of symptomatic Covid-19 infections among health care workers between February 21 and May 19. As many as 1,350 staff tested positive and 32 of them developed an infection within two weeks of the second dose.
“Protection began even after the first dose. Single dose provided 95% protection from ICU admission. However, note that we don't know what proportion of cases were due to B.1.617.2 (delta variant) or B.1.617.1 variant or wild type,” said Priya Sampathkumar, chair, infection prevention and control at Mayo Clinic, USA.
“Our study corroborates these studies that vaccination is protective, although we did not look at the variants responsible for the massive second wave,” said team leader Joy Mammen, a professor at CMC. “Even as many states chose to restrict movement to reduce stress on the healthcare system, we realize that future waves can at best be prevented or at worst mitigated through aggressive and widespread vaccination.”
While more than one crore healthcare workers received the first dose of the vaccine, less than 70 lakh received the second dose till Thursday, even though vaccination for the healthcare workers began five months ago as they were the priority group. The Centre has now asked the states to expedite the second dose vaccination for healthcare and frontline workers.