A cross-sectional survey of nearly 6,000 people across age groups including those over 80 years of age carried out through email and social media platforms between February 15 and March 10, 2022 in the midst of the third wave in India that lasted from late December 2021 and lasted till March 2022 has thrown up some interesting findings.
The government had greenlighted a precaution or booster dose to everyone above 60 years with comorbidities and health-care and frontline workers from January 10, 2022. Though the booster dose was to be administered only after nine months following the second dose, there have been accounts of people who had received a booster dose less than nine months after the second dose.
The Omicron variant
According to the results posted as a preprint (which is yet to be peer-reviewed) on April 28, 2022, of the 2,383 people who received a booster shot, 716 (30%) were infected by the Omicron variant. In comparison, of the 3,505 people who had not received a booster shot, 1,577 (45%) were infected by the Omicron variant. Interestingly, infection in 77% of people during the third wave was two weeks or more after receiving the precaution dose. That would mean that infection had occurred despite there being sufficient time for the immune system to be boosted by the precaution dose.
The increased chances of infection among those who had not received a booster dose could also be because of lower usage of N95 masks. The survey found that only 50% of respondents who did not receive a booster shot used N95 masks compared with 68% in the group that took the booster shot.
“The findings of the survey once again underline the ability of the Omicron variant to cause infection when protection conferred by the booster dose is supposed to be maximum,” says Dr. Rajeev Jayadevan, co-chairman, National IMA COVID Task Force, and a co-author of the preprint. “The higher N95 mask usage too could have played a role in reducing the risk of infection among the boosted group.”
The respondents cited several reasons for not taking a booster shot despite it being available for free. The most important reason mentioned was that infections were commonly reported among people who had taken the precaution dose. The other stated reasons for not taking the booster shot were: 1) belief that prior infection would be protective, 2) lack of enough evidence, 3) adverse experience with prior doses of vaccine, 4) concern that mutations have altered the virus since the vaccine was originally made, 5) two doses were enough, and 6) waiting for mix-and-match booster vaccines.
Disease severity
Another important finding of the survey was regarding the disease severity among people who had taken the booster shot and those who had not. Immaterial of the booster dose status, only less than 1% of the respondents had severe COVID-19 disease and 41.5% had developed moderate disease. Among the 716 people who had taken the booster dose and got infected, 58.5% had mild disease, 37% had moderate disease and 0.3% had severe disease. In comparison, among the 1,577 people who had not taken a booster shot and got infected, 50.8% had mild disease, 43.4% had moderate disease and 0.76% had severe disease.
“Immaterial of whether an individual had received two or three doses, the severity trend of disease was the same. The booster dose only reduced the chances of getting infected,” says Dr. Jayadevan.
This finding once again underlines the effect of full vaccination with two doses in protecting against severe disease, and surprisingly very little additional benefit that the booster dose offers in preventing the progression of the disease especially in the elderly.
“According to the findings of our survey, the booster dose appears to reduce the odds of picking up an infection at least in the early period after the booster shot but does not seem to alter the trend of disease severity,” says Dr. Jayadevan. This finding completely contradicts the general notion that people older than 60 years might be only partially protected by two doses and a booster dose to this group would confer greater degree of protection against disease severity.
One more interesting finding of the survey is the protective effect of the vaccine from infection both in the case of the second dose and the booster dose. “Among those who had recently received their second dose, only 27% (59/221) were positive in the third wave, which was about the same as that following the booster dose (30%). This suggests that infection was less likely among those who had recently received a vaccine dose,” they write.
Protective effect
Another interesting highlight of the survey was the nearly equal protective effect of both Covishield and Covaxin against infection by the Omicron variant. The nearly equal protective effect from either vaccine was seen in people who had taken only two doses of the vaccine and in those who had also received the booster shot.
Other factors including strict adherence to mask wearing and other COVID-appropriate behaviour among people who have received either of the vaccines is not known. While the percentage of people infected is comparable between the two vaccines, the number of respondents who had received Covishield is many times more than those who had taken Covaxin.
Asymptomatic infection
As expected, 44% of respondents did not report any known history of COVID-19, which might be a reflection of asymptomatic infection in these people or not getting themselves tested. At the same time, a large number of people (15% of those with a history) reported having COVID-19 more than once.
“Among them, 454 people had it twice, 26 people thrice and 12 individuals reported up to five times,” they authors write. They also add: “The reinfection percentage of 15% is likely to be an underestimate because several respondents clarified that in subsequent episodes with compatible symptoms, testing was not always done.”
