Early in the pandemic, vaccines were often seen as the savior that would defeat COVID and return life to normal. Unfortunately, it hasn’t quite worked out that way.

"The vaccine strategy has been extremely effective at reducing the risk of progression to severe disease, but current vaccines don’t prevent transmission of coronavirus," said Ziyad Al-Aly, a clinical epidemiologist at Washington University in St. Louis.  

Although the fact that vaccinated people can get reinfectedwith COVID has become scientific consensus, how these reinfections compare in severity with initial infections has been less clear — until now. 

Al-Aly is the lead author of a new study published Thursday that shows reinfection causes a higher risk of health concerns than initial infection.

Coronavirus reinfection increases health risks

The paper, published in Nature Medicine, shows that getting infected with COVID a second time is associated with an increased risk of acute problems in the 30 days following infection. It also showed an increased risk of post-acute problems during the long COVID phase. 

"We’re not advocating for draconian measures, but going into the winter season, policymakers and individuals can do things within their means to try to reduce risk at the population level," Al-Aly told DW. 

Largest coronavirus reinfection study to date

Al-Aly, who also works as a clinician, started seeing patients who’d been infected with COVID multiple times, even if they had been vaccinated.

"Many people thought they would have a sort of super immunity against the virus, and a second infection wouldn’t matter. We thought we didn’t really know if that’s true, so wanted to study whether reinfection really matters," he said.

The authors used the US Department of Veterans Affairs’ healthcare database to investigate the risks involved with COVID reinfection. The database included a total of over 5.3 million people, including 40,947 people who’d had two or more COVID infections.

Overall, the study found that COVID reinfection overwhelmingly increases adverse health risks.

Compared to no reinfection, having COVID a second time increased risk of death twofold, and risk of hospitalization threefold.

What’s more, repeated coronavirus reinfections increased the risk of adverse health effects with each reinfection.

"What a two- or three-fold increase in risk means for an individual is hard to determine. But the underlying message is that people need to be aware that reinfection carries risk, and it’s not trivial," Al-Aly said.

Vaccine impact still unclear

The study failed to include some important elements, outside experts say. 

"This study does not mention the impact of vaccines on reinfection risks," said Beate Kampmann, a professor of pediatric infection and immunity at the London School of Hygiene and Tropical Medicine.

According to Kampmann, understanding the impact of vaccines on COVID reinfection could be crucial to monitoring health outcomes.

"Reinfection data can also tell us about ways of better protecting people against coronavirus," she said. "For example, if we understand the immune response to reinfection better, we can deduce what a vaccine needs to achieve."

"However this might change if we see new variantsor dramatically waning immunity. We need more longitudinal studies to examine this," Kampmann added.

White male database might limit meaning for wider public

Kampmann also pointed out that the study mostly included older white American males — over 90% — meaning it could be difficult to extrapolate the data to other demographics.

The study authors also acknowledge this limitation, but stated they adjusted the hazard ratios for ages, sex and race in the study.

"There may be people with higher risk than others, but the average risk we measured was independent of underlying characteristics of the population. Because of the size of the study, the representation from different groups likely holds for the population," said Al-Aly.

New vaccine strategy needed for true long-term protection?

Experts have long been calling for a renewed vaccination strategy to provide better and more long-term protection against COVID.

Al-Aly is one of those calling for a vaccination strategy 2.0, and stated the biggest challenge is to create vaccines that both prevent transmission of coronavirus and provide protection that lasts for several years.

"This is what we need to do to truly adapt to the virus, otherwise we’ll be wearing masks for the next hundred years," he said.

On the upside, the science and technology is already there to do this. Nasalvaccines that produce mucosal immunity to block transmission for multiple years are currently being developed, with promising results.

"We now need governments to fund and develop the technology to bring it to the public," Al-Aly said.

Coronavirus

Edited by: Clare Roth