Study shows protection against reinfection for COVID-19 vaccines

A new study from Denmark suggests that COVID-19 vaccines provide good protection against reinfection in people who have already contracted the virus, sometimes for up to 9 months. The study, which looked at the protection provided during the Alpha, Delta and Omicron waves, is published in PLOS medicine.

The study population included more than 700,000 people with a previous SARS-CoV-2 infection identified in national Danish registries from January 1, 2020 to January 31, 2022. The authors estimated vaccine effectiveness (VE) for different variant periods, and by time since vaccination with non-vaccinated citizens as reference.

VE against reinfection after any type of COVID-19 vaccine administered in Denmark peaked at 71% (95% confidence interval [CI]-Inf to 100%) at 104 days or more after vaccination during the Alpha period, 94% (95% CI, 92% to 96%) 14 to 43 days after vaccination during the Delta period, and 60% (95% CI , 58% to 62%) 14 to 43 days after vaccination during the Omicron period.

“While vaccination appears to protect against re-infection with the Omicron variant to a lesser extent, these findings are of public health significance as they demonstrate that previously infected individuals still benefit from COVID-19 vaccination across all three variants,” said the authors. .

New variants smooth VE estimates

In an email to CIDRAP News, first study author Katrine Finderup Nielsen, MS, said the study purposefully excluded vaccine recipients infected less than 90 days prior, but did not account for booster doses administered after January 2022.

Gregory Poland, MD, of the Mayo Clinic’s Vaccine Research Group in Rochester, Minnesota, said the study confirms that vaccination protects against reinfection for at least several weeks, but new variants make studying VE difficult for researchers.

“The problem is that this is a multidimensional matrix made up of what you got infected with, what vaccines you’ve had, how many, how long ago and what’s circulating now,” Poland said.

He believes previous natural infection with COVID-19 and two vaccine doses mean that someone who is re-infected is very unlikely to die or even end up in hospital with a subsequent case, but the risk of developing acute and post-COVID symptoms is real. .

“The risk of long-term COVID is 20% to 25%. The risk of complications from acute infections ranges from 20 to almost 100 per thousand cases,” said Poland. “Remember, 1 in 298 Americans is dead from COVID-19.”

Holiday warning

Ziyad Al-Aly, MD, chief of the research and education service at Veterans Affairs St. Louis Health Care System, has published recent studies on reinfections in vaccinated people. His message is clear: “People who are re-infected are still at risk for problems and long-term COVID. Reinfections are not benign.

“The virus always outperforms and outsmarts us. We do a study on Delta, then Omicron comes out, but what we’re seeing now is the hybrid immunity of vaccine-derived immunity and natural infection is not a complete shield.”

Al-Aly and Poland both said their message, while sobering, is important as Americans embark on a six-week holiday season that begins tomorrow with Thanksgiving.

First, while not foolproof, both recommended that people get all vaccines and boosters on the proposed timeline as outlined by the Centers of Disease Control and Prevention.

Al-Aly said he would advise wearing a properly fitted mask on holiday trips, and Poland says a proper mask is just as important to people as wearing a seatbelt in a car. Optimal protection is provided by wearing a close-fitting respirator such as an N-95.

“There will be people who will read this and by Christmas they will be dead or in the hospital,” Poland said. “So we need to balance known risks and known benefits and make choices based on data.”

Leave a Comment