A questionnaire-based survey conducted by a group of Kochi-based doctors among 5,971 adults across the country to assess the community level experience of the pandemic, with focus on the third wave and vaccination, has reported that 30% of the respondents who had taken the third dose (2,383 persons) had contracted COVID-19 during the third wave.
The percentage of severe disease (defined as the proportion who required supplemental oxygen during hospitalisation) during the third wave remained below 1% among all vaccinated individuals, whether they received the third dose or not. Moderate severity was reported by 42% of those affected during the wave.
About 98.6% of the individuals in the study were fully vaccinated. Among those who did not take a third dose, 45% reported COVID-19 in the third wave.
Interestingly, both Covaxin and Covishield recipients had the same incidence of COVID-19 –40% and 39% respectively – during the third wave, suggesting that the protection rendered by the primary dosage of both vaccines were almost the same.
Among individuals who contracted a breakthrough infection after the third dose, 77% got infected after two weeks of getting the third dose, indicating that sufficient time had passed after receiving the third shot for antibody levels to be boosted.
The study reported that the longer the gap after the second dose, the greater was the likelihood of becoming infected during the third wave. Accordingly, when 27% of those who had had a recent second dose got infected during the third wave, 30% of those who had received a recent third dose also got infected.
This suggested that proximity to the most recent vaccine dose, whether it was the second or the third, is an important determinant of protection from infection and that frequent vaccine doses will not add anything further to pre-existing protection.
“Though the trend suggests that infection rate during the third wave was lower among those who took the third dose (30%) than among those who had not taken it (45%), the proportion of those who developed severe disease (<1% ) was no different for those who had two doses or three doses. This means that the primary protection offered by the basic two doses is very effective,” said Rajeev Jayadevan, co-chairman of National IMA COVID Taskforce, who led the study. Ramesh Srinivasa Shenoy and Anithadevi T.S. were part of the team.
Dr. Jayadevan, however, specified that a survey cannot be equated to a randomised control trial and hence the findings cannot be taken as an exact measure of the effectiveness of booster doses.
In other words, the efficacy of or the level of protection rendered by a third booster/precautionary dose of COVID-19 vaccine, against re-infection or in reducing disease severity, continues to be a grey area.
Notably, 15% of the severe cases during the third wave were reinfections, and occurred among vaccinated individuals. This disproves the popular notion that reinfections are always milder than the first episode.
“The reinfection rate of 15% is likely an underestimation as people may not test during subsequent bouts. This is an area that needs further study, because we have no idea about the long-term consequences of multiple COVID reinfections. Re-infections are not necessarily milder, nor does it offer any additional immune protection. People should continue to use masks and protect themselves as far as possible from getting COVID-19,” said Dr. Jayadevan.
The third wave in India lasted from January till March 2022, and breakthrough infections were common. The third/precautionary dose of vaccine was rolled out to priority groups in early January 2022.
