Covid vaccine protection short-lived, booster shots important: Study

Strong protection following Covid-19 vaccination is short-lived, making an additional booster shot necessary for individuals, according to a study.

The research, published in the journal Proceedings of the National Academy of Sciences, is the first to quantify the likelihood of future infection following natural infection or vaccination by the Moderna, Pfizer, Johnson & Johnson, or Oxford-AstraZeneca vaccines.

The researchers noted that the risk of breakthrough infections, in which a person becomes infected despite being vaccinated, depends on the vaccine type.

The study found that current mRNA vaccines -- Pfizer and Moderna -- offer the greatest duration of protection, nearly three times as long as that of natural infection and the Johnson & Johnson, and Oxford-AstraZeneca vaccines.

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"The mRNA vaccines produce the highest levels of antibody response and in our analysis confer more durable protection than other vaccines or exposures," said Jeffrey Townsend, a professor at Yale School of Public Health, US, and the study's lead author.

"However, it is important to remember that natural immunity and vaccination are not mutually exclusive. Many people will have partial immunity from multiple sources, so understanding the relative durability is key to deciding when to provide a boost to your immune system," Townsend said.

Dependable protection against reinfection requires up-to-date boosting with vaccines that are adapted to address changes in the virus that occur as part of its natural evolution over time, the researchers said.

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"We tend to forget that we are in an arms race with this virus, and that it will evolve ways to evade both our natural and any vaccine-derived immune response," said Alex Dornburg, assistant professor at the University of North Carolina at Charlotte, who led the study with Townsend.

"As we have seen with the Omicron variant, vaccines against early virus strains become less effective at combating new strains of the virus," Dornburg said.

The researchers' data-driven model of infection risks through time takes advantage of the striking similarities of reinfection probabilities between endemic coronaviruses which cause common colds and SARS-CoV-2, the virus that causes Covid-19.

These similarities allowed the scientists to make longer-term projections than studies focused solely on current-day infections.

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The model placed antibody responses following natural and vaccine-mediated immunity into the same context, enabling comparison.

"SARS-CoV-2 mirrors other endemic coronaviruses that also evolve and reinfect us despite natural immunity to earlier strains," said Townsend.

"Continual updating of our vaccinations and booster shots is critical to our fight against SARS-CoV-2," he added.