Do booster shots work?

Booster injection to increase immunity or COVID-19 vaccine booster dose concept. Third booster shots vaccine after primer dose. Illustrator vector of Vaccine bottle, syringe, needle and calendar.  

Studies from Israel and the U.S. have documented increased incidence of breakthrough infections a few months after the second dose of the mRNA vaccines. The Israel study showed that the waning immunity after the second dose was not only responsible for breakthrough infections but also severe disease in some people, with older people being particularly vulnerable. Though a small proportion of fully vaccinated people tend to suffer from severe disease and death, all COVID-19 vaccines have so far been found to be largely effective in protecting the fully vaccinated from hospitalisation and death.

The increased incidence of breakthrough infections has led to a few countries administering booster shots.

Now, a small study involving just 33 participants measured the antibody responses before and soon after a booster dose was administered. These participants had already received two doses of either the Pfizer or Moderna mRNA vaccine with or without prior infection. The study found “large antibody responses” soon after the booster dose was administered. The study is posted as a preprint in the medRxiv server. (Preprints are yet to be peer-reviewed and published in scientific journals.)

Studies to measure virus neutralisation against the Delta variant were also undertaken. The researchers found that a booster dose still has “high” capability to neutralise the Delta variant. However, the efficacy to neutralise the Delta variant is relatively low compared to the wild-type SARS-CoV-2 strain found during the early days of the pandemic. In short, the efficacy to neutralise the Delta variant even after a booster shot did not become comparable with the strains that were in circulation early during the pandemic. The ability to neutralise the Delta variant was also lower in older people compared with younger age groups.

“The study indicates that mRNA boosters generate large antibody responses in healthy adults, with post-booster antibody levels that exceed levels documented after natural infection with COVID-19, after two doses of vaccine, or after both natural infection and vaccination,” they write. They add: “These data support the use of boosters to prevent breakthrough infections and suggest that antibody-mediated immunity may last longer than after the second vaccine dose.” But they found that post-booster shot, the IgG level was negatively associated with age; the median age was 43 years. In other words, older people tend to have a relatively lower IgG antibody concentration even after a booster shot compared with younger people.

The very purpose of a booster shot in older people and those who are immunocompromised is because the antibody levels tend to wane faster in these categories of people than in younger people even after full vaccination. But the current study shows that even after a booster shot, the difference in antibody concentration in older people vis-a-vis younger people would continue to persist.

Besides the small number of participants included in the study, there is another limitation — the antibody levels were measured soon after the booster was administered (6-10 days). Since the antibody measured was soon after the booster dose was given, the study only reflects the level of antibody response but not the duration to which the increased immune response persists. Also, the study did not measure cellular immunity such as T cell and B cell-mediated immunity.

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Printable version | Dec 6, 2021 7:56:07 AM | https://www.thehindu.com/sci-tech/science/do-booster-shots-work/article37638694.ece

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