Booster dose may not change trend in disease severity: study


There were fewer infections in people who received a booster dose compared to those who did not receive a booster

There were fewer infections in people who received a booster dose compared to those who did not receive a booster

A cross-sectional survey of nearly 6,000 people of all ages, including the over 80s, conducted via email and social media platforms between February 15 and March 10, 2022 amid the third wave in India which lasted at the end of December 2021 and lasted until March 2022 gave interesting results.

The government had given the go-ahead for a precautionary or booster dose for all people over 60 with comorbidities and healthcare and frontline workers from January 10, 2022. Although the booster dose was not to be given until nine months after the second dose, there have been accounts of people receiving a booster dose less than nine months after the second dose.

The Omicron variant

According to results published in preprint (which have not yet been peer-reviewed) on April 28, 2022, of the 2,383 people who received a booster, 716 (30%) were infected with the Omicron variant. By comparison, of the 3,505 people who did not receive a booster, 1,577 (45%) were infected with the Omicron variant. Interestingly, infection in 77% of people in the third wave was two weeks or more after receiving the precautionary dose. This would mean that the infection occurred when there was enough time for the immune system to be boosted by the precautionary dose.

The increased risks of infection among those who did not receive a booster dose could also be due to less use of N95 masks. The survey found that only 50% of respondents who did not receive a reminder used N95 masks, compared to 68% in the group who took the reminder.

“The survey results again underscore the ability of the Omicron variant to cause infection when the protection conferred by the booster dose is expected to be maximal,” says Dr. Rajeev Jayadevan, co-chair of the national IMA working group. COVID, and a co-author of the preprint. “The higher use of the N95 mask could also have played a role in reducing the risk of infection among the boosted group.”

Respondents cited several reasons for not taking a reminder when it was available for free. The most important reason mentioned was that infections were frequently reported in people who took the precautionary dose. Other reasons given for not taking the booster dose were: 1) belief that previous infection would be protective, 2) lack of sufficient evidence, 3) adverse experience with previous doses of vaccine, 4) fear that mutations have changed the virus since the vaccine was originally made, 5) two doses were enough and 6) waiting for mixed boosters.

disease severity

Another important finding from the survey concerned the severity of illness in people who took the booster and those who did not. Regardless of booster dose status, only less than 1% of respondents had severe COVID-19 disease and 41.5% developed moderate disease. Of the 716 people who took the booster dose and became infected, 58.5% had mild disease, 37% moderate disease and 0.3% severe disease. By comparison, of the 1,577 people who had not taken a booster and were infected, 50.8% had mild disease, 43.4% had moderate disease and 0.76% had severe disease.

“It didn’t matter whether an individual received two or three doses, the trend in disease severity was the same. The booster dose only reduced the risk of infection,” says Dr Jayadevan.

This finding underscores once again 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 disease progression, particularly in the elderly.

“According to the results of our investigation, the booster dose appears to reduce the chances of acquiring an infection at least in the early period following the booster dose, but does not appear to alter the trend in disease severity,” says the Dr Jayadevan. This finding completely contradicts the general notion that people over the age of 60 may be only partially protected by two doses and a booster dose to this group would confer a greater degree of protection against disease severity.

Another interesting finding from the survey is the protective effect of the vaccine against infection in both 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 at the third wave, which was about the same as that following the booster dose (30%). This suggests that the infection was less likely in 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 Covishield and Covaxin against Omicron variant infection. The almost equal protective effect of either vaccine was seen in people who took only two doses of the vaccine and in those who also received the booster.

Other factors, including strict adherence to mask-wearing and other COVID-appropriate behaviors among people who have received either vaccine, are not known. While the percentage of people infected is comparable between the two vaccines, the number of respondents who had received Covishield is much higher than those who had taken Covaxin.

Asymptomatic infection

As expected, 44% of respondents reported no known history of COVID-19, which could be a reflection of asymptomatic infection in these people or not getting tested. At the same time, a large number of people (15% of those with a history) reported having had COVID-19 more than once.

“Among them, 454 people had it twice, 26 people three times, and 12 people reported it up to five times,” the authors write. They also add: “The 15% reinfection percentage is likely an underestimate as several respondents clarified that in later episodes with consistent symptoms, testing was not always done.”

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