As many countries once again ramp up restrictions designed to limit the coronavirus’ spread in the wake of the Omicron variant, understanding the prevalence and cause of long COVID among vaccinated people has critical public health implications. Although vaccines vastly reduce the likelihood of serious illness and death from COVID-19, they are not guaranteed to completely prevent infection, and long COVID can occur even after a mild or completely asymptomatic case. 

In addition, many people with mild or asymptomatic infections might not get a COVID test, says immunologist Petter Brodin at the Karolinska Institute in Stockholm. “Doing any kind of assessment of how many people develop long-term symptoms after they are vaccinated is going to be incredibly difficult.”

Could Vaccination Help Prevent Long-COVID Symptoms?

One theory concerning the cause of long COVID is that the virus lingers in various tissues–such as the intestines, liver, or brain–after the acute infection, and continues to cause damage. Another possibility is that the extensive immune response marshaled by the initial infection can also trigger an autoimmune response in which antibodies attack healthy cells and tissue. 

If a vaccine generates high levels of antibodies and T cells that can recognize the virus, it could reduce the chances of such events. The immune system could conceivably halt the virus from replicating before it establishes hiding spots in the body, says Yale University immunologist Akiko Iwasaki. Vaccination also enables the body to launch a more target-specific immune response from the moment of infection.

How Common Is Long COVID in Breakthrough Infections?

Determining exactly how common long COVID is in breakthrough infections is a challenge, though attempts are ongoing. A study conducted by a partnership between data-science company ZOE and King’s College London collected data from 1.2 million participants who received at least one dose of a COVID-19 vaccine and logged their experience in the COVID Symptom Study app. 

The analysis showed that a full vaccination reduced the risk of long COVID (defined as lingering symptoms for at least 28 days post-infection) by about half among those who had breakthrough infections. Despite lopsided demographics regarding gender and income level, says Claire Steves, a geriatrician at King’s College and lead author of the study, the results clearly show that vaccination considerably reduces both infection rates and symptom severity. 

These findings are supported by a study of U.S. veterans, in which COVID-19 vaccines provided about 50% protection against coronavirus infection, even during the Delta surge. 

Could Vaccination Help Improve Long-COVID Symptoms?

One theory concerning the Delta variant’s virulence is that infectious particles exhaled by people with the variant carry a higher viral load. This could enable Delta cells to replicate more readily than those of other variants, says Iwasaki, even in people who are fully vaccinated. This would make it easier for the virus to find hiding places and/or trigger a massive immune response, which could facilitate the development of long COVID.

The continuation of both vaccination programs and research studies will teach us how different variants and vaccines affect long COVID. Studies are also exploring how vaccination may help relieve long-COVID symptoms. This past October, the UK Office for National Statistics reported that a first dose of a COVID-19 vaccine was linked with a 13% decrease in self-reported long-COVID symptoms among those with the condition. A second dose reduced symptoms by an additional 9%, though the duration of these effects is not yet clear.

The RECOVER Study

Last December, Congress allocated the NIH $1.15 billion over four years to study the long-term health consequences of SARS-CoV-2 infections. This past June, the NIH granted the first award for a long-COVID research program called RECOVER, which aims to track the symptoms of tens of thousands of participants, including some that have not been infected, and those with and without long COVID after an acute infection. One of the primary goals is to glean more information about the development of long COVID and better define it.

Data the RECOVER team hopes to gather include:

• Rates of long COVID among those who are vaccinated
• The duration and nature of each participant’s symptoms
• The coronavirus variant responsible for each participant’s illness

The team hopes to complete enrollment in the program’s first year, an ambitious goal that illustrates the urgent need to improve long-COVID treatment and care, Iwasaki says. RECOVER will also collect data on vaccinated children and adolescents–a noticeable gap in the existing literature. 

*Ledford, H. (2021, Nov. 23). Do Vaccines Protect Against Long COVID? What the Data Say. Nature. https://www.nature.com/articles/d41586-021-03495-2 

Much about the novel coronavirus, i.e., COVID-19, is still not fully understood. As research progresses and our knowledge of the virus increases, information can change rapidly. We strive to update all of our articles as quickly as possible, but there may occasionally be some lag between scientific developments and our revisions.