With the vaccination drive against Covid-19 expanding every day, the number of people in India who are fully vaccinated stands at over 5 crore, while over 21 crore people have received the first dose of the vaccine. Since all the currently available vaccines comprise two doses, the Centre is urging everyone, especially frontline workers, to complete the course by getting both doses. Having said that, the Centre has also said that the first dose too offers some protection. But it is not desirable to take only one shot, it has been reiterated.
First dose versus 2nd dose
According to a PGI Chandigarh study, vaccine effectiveness is 75 per cent for all those who received the first dose and both doses. The government’s Covid-19 expert group chairman Dr NK Arora has said that the study proves that at least in the short run, effectiveness is similar notwithstanding whether one has received one dose or both doses. “If you received only one dose, still you are protected,” Dr Arora said.
Another study on Covishield reveals that the protection of one dose is around 61 per cent, and for two doses it’s 65 per cent.
“A few days back, another very important study by CMC Vellore, Tamil Nadu which covers most of the current epidemic wave India experienced in April and May 2021 shows that if somebody is partially immunized, vaccine effectiveness of Covishield is 61% and with two doses, the effectiveness is 65% – and there is very little difference, especially since there is some degree of uncertainty involved in these calculations,” the Centre has said.
Chances of reinfection after the first dose and 2nd dose
Chances of reinfection after vaccination is not negligible as incidents of infection between the doses have also been reported. The Centre said two organisations in Delhi are studying vaccine efficiency. “And both these studies show that breakthrough infection with one dose is around 4%, and around 5% with two doses, basically hardly any difference. And the other study shows that 1.5% – 2% breakthrough infections,” the government said.
Why is the efficiency of the 1st dose in question?
The government has extended the gap between the first dose and the second dose of the Covishield vaccine to three months. Hence, it is being studied how long the first dose protects. For Covaxin, the gap between the doses remains 28 days but the efficiency of one dose is also being studied.
What do international studies say?
Public Health England has recently said that the protection of the first shot of the Oxford vaccine (Covishield in India) is not as much as it was thought earlier. Hence, a few countries are again narrowing the gap between the doses of Oxford vaccine.