There have been reports of breakthrough cases among people even after getting vaccinated against COVID-19, but there are less chances of the infection resulting in hospitalisation or death. But one important question about breakthrough infection that remains unanswered is: Can the vaccinated develop so-called long COVID?

Long COVID means that patient suffers severe fatigue, brain fog, headache, muscle pain and sleep problems for weeks or months after the active infection has ended. This condition has not been understood properly, but according to studies, over 30% of infected adults may experience long COVID, including those who experienced only mild illness or no symptoms at all.

According to New York Times, this vast majority of data about long COVID is only about the unvaccinated population. The risk of a vaccinated person developing long COVID has not been studied yet.

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If preliminary research is to be believed, there is in fact a possibility for a breakthrough case to lead to symptoms that can persist for weeks to months. But, experts say there are still more questions that need to be answered. What is percentage of vaccinated people experiencing lingering symptoms? How many of those people recover?

Dr Zijian Chen, medical director at the Center for Post-COVID Care at Mount Sinai Health System in New York told NYT that there was not enough data and it was too early to tell. “The population of people getting sick post vaccination isn’t that high right now, and there’s no good tracking mechanism for these patients,” he added.

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According to a recent paper of Israeli health care workers, which was published in the New England Journal of Medicine, the risk of long COVID after a breakthrough infection was studied. A total of 1,497 fully vaccinated health care workers were reviewed. Of 1,497, 39 reported COVID infection.

These health workers had mild symptoms or were asymptomatic. Only seven out of 36 workers reported persistent symptoms even after six weeks. These long COVID symptoms included a mix of prolonged loss of smell, persistent cough, fatigue, weakness, labored breathing or muscle pain.

The study’s authors said the sample size was too small to come any conclusion. This study is the first indication from a peer-reviewed study that long COVID is possible after a breakthrough infection.

Meanwhile, the US Centers for Disease Control and Prevention is at present only tracking post-vaccination infections resulting in hospitalisation or death. There is lack of data on all breakthrough cases.

“It’s very frustrating not to have data at this point in the pandemic to know what happens to breakthrough cases,” said Akiko Iwasaki, an immunologist at Yale School of Medicine who is conducting studies of long COVID.

There are some experts who predict delta variant will lead to more breakthrough cases in the coming months.

Even though there is lack of data, Athena Akrami, a neuroscientist at University College London, said getting vaccinated will reduce the risk of getting infected and getting long COVID.