Booster dose may not alter disease severity trend: study

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

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

A cross-sectional survey of nearly 6,000 people across age groups, including those over 80 years old, conducted via 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 to March 2022 has yielded some interesting findings.

The government had given the go-ahead for a precautionary or booster dose for anyone over the age of 60 with co-morbidities and health and front-line workers as of January 10, 2022. Although the booster dose would not be given until nine months after the second dose, there are reports of people receiving a booster dose less than nine months after the second dose.

The Omicron variant

According to the results posted as preprint on April 28, 2022 (which is yet to be peer reviewed), of the 2,383 people who received a booster injection, 716 (30%) were infected with the Omicron variant. In comparison, of the 3,505 people who had not received a booster injection, 1,577 (45%) were infected with the Omicron variant. Interestingly, the infection occurred in 77% of people during the third wave two weeks or more after receiving the precautionary dose. That would mean that an infection has occurred despite there being enough time for the immune system to be strengthened by the precautionary dose.

The increased risk of infection in those who did not receive a booster dose could also be due to lower use of N95 masks. The study found that only 50% of the respondents who did not receive a booster injection used N95 masks, compared to 68% in the group that took the booster injection.

“The findings of the study once again underscore the ability of the Omicron variant to cause infection when the protection afforded by the booster dose would be maximal,” said Dr. Rajeev Jayadevan, co-chair of the National IMA COVID Task Force, and a co-author of the preprint. “Also, the higher N95 mask usage could have played a role in reducing the risk of infection in the boosted group.”

The respondents mentioned several reasons for not taking a booster injection, despite it being available for free. The main reason given was that infections were often reported in people who had taken the precautionary dose. The other reasons cited for not taking the booster shot were: 1) belief that a previous infection would be protective, 2) lack of sufficient evidence, 3) adverse experience with previous doses of vaccine, 4) concern that mutations have altered the virus since the vaccine was originally made, 5) two doses were enough, and 6) wait for mix-and-match booster vaccines.

Severity of the disease

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

“It doesn’t matter if a person had received two or three doses, the disease severity trend was the same. The booster dose only reduced the chance of contamination,” says Dr Jayadevan.

This finding once again underscores the effect of full two-dose vaccination to protect against serious disease, and surprisingly little additional benefit that the booster dose provides in preventing disease progression, especially in the elderly.

“According to the findings of our study, the booster dose appears to reduce the likelihood of contracting an infection, at least in the early period after the booster injection, but does not appear to change the trend in disease severity,” said Dr. Jayadevan. This finding completely contradicts the common notion that people over the age of 60 are only partially protected by two doses and a booster dose for this group would provide a greater degree of protection against the severity of the disease.

Another interesting finding of the study is the protective effect of the vaccine against infection, both at the second dose and at the booster dose. “Of those who had recently received their second dose, only 27% (59/221) were positive in the third wave, which was about the same as after the booster dose (30%). This suggests that infection was less likely in those who had recently received a vaccine dose,” they write.

Protective effect

Another interesting highlight of the study was the nearly equal protective effect of both Covishield and Covaxin against infection by the Omicron variant. The almost equal protective effect of both vaccines was seen in people who took only two doses of the vaccine and in those who also received the booster shot.

Other factors, including strict adherence to mask-wearing and other COVID-appropriate behavior in people who have received any of the vaccines, are unknown. Although the percentage of people infected is similar between the two vaccines, the number of respondents who received Covishield is many times greater than the number of respondents who took Covaxin.

Asymptomatic infection

As expected, 44% of respondents reported no known history of COVID-19, which may reflect an 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 had COVID-19 more than once.

“Among them, 454 people had it twice, 26 people three times and 12 people reported up to five times,” the authors write. They also add, “The reinfection rate of 15% is likely an underestimate, as several respondents clarified that subsequent episodes with compatible symptoms were not always tested.”


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