Does a booster dose of Omicron help prevent re-infection?

It appears that those who received booster vaccines are more likely to be reinfected with the mutated coronavirus than those who received the initial series of vaccines.

That’s the conclusion of a recent statistical study conducted by Hiam Al-Shamitali, PhD, in epidemiology and population health at Weill Cornell Medicine in Qatar – the Infectious Disease Epidemiology Group and his colleagues, published on October 4, 2023, in the journal Science Advances. .

Success of vaccines against the first strain

In 2022, the Covid-19 pandemic was brought under control, and the World Health Organization declared it a global health emergency on May 5, 2023. This success is largely due to the rapid development and distribution of effective vaccines for SARS-CoV-2. Some of these vaccines have shown more than 90 percent effectiveness in trials. By 2021, widespread immunity to the original virus strain was achieved through global vaccination efforts.

“Omicron” bypasses acquired immunity

However, by the end of 2021, a highly infectious “Omicron” variant appeared and was genetically different from the original strain. Omicron’s ability to evade immune responses trained to the original virus led to its rapid spread even among vaccinated individuals, and it became clear that existing vaccines were less effective against Omicron. The strains of the virus are new.

Injury data analysis study

The study analyzes population health data from Qatar to investigate epidemiological evidence for such an immune signature. The Omicron variant compared the risk of reinfection after a previous infection among populations with a different history of mRNA vaccination prior to any documented natural infection.

The study compared the risk of reinfection with Omicron among three groups: those who were not vaccinated, those who received two doses of the vaccine, and those who received a booster dose after two doses.

The researchers followed the individuals over time, starting three months after the initial infection with Omicron. They found that those who received two doses of the vaccine had a lower risk of reinfection.

High risk of infection

However, those who received a booster dose were about 50 percent more likely to become infected again compared to those who received two doses, suggesting a greater risk of reinfection in individuals vaccinated with a booster dose.

Compared to those who received three doses, it appeared that people who received two doses of the vaccine may have better immunity to Omicron because those who received two doses appeared to have fewer immune events as a result of the vaccine, allowing them to mount. A high immune response is effective against “Omicron”.

Therefore, giving booster doses may not be beneficial and may even be harmful in some cases.

Questions about the results of the study

However, the study results should be interpreted with caution. It is worth noting that the study design has limitations.

Some experts said the comparison between the three-dose and two-dose groups was biased because those in the three-dose group received a booster shot shortly before exposure to Omicron, making them more susceptible to infection.

In contrast, individuals who received two doses received their initial vaccination, so the protective effect may have been reduced. Therefore, because the two-dose group represents a broader portion of the population, the study’s assumption that these two groups are similar in terms of the likelihood of relapse is questionable.

Difficulty evaluating results accurately

For his part, Christian Hansen, Associate Professor of the Department of Epidemiology of Infectious Diseases at the London School of Hygiene and Tropical Medicine, London, said in his research published in the same journal on October 4 this year. , he has a different opinion. He says it is difficult to accurately assess the impact of various biases that may have affected the results of the studies conducted by Hiam Al-Shemaitli and his team.

In observational studies of vaccine efficacy, comparisons of infection rates are valid in the short period after vaccination, but over time the effects of selection and other biases increase, affecting over time. Patterns observed long after vaccination. Researchers in the study determined the infection rates by analyzing the results of the “SARS Cove 2” trial from national databases, because these infection rates are not only affected by the actual infection in the comparison groups, but also by the tests. Behaviors that differ between groups and change over time.