COVID-19 Vaccines and Hyperglycemia in Patients with Type 1 Diabetes

While proven to be safe, the COVID-19 vaccines could cause some people with type 1 diabetes to see their blood sugar to temporarily spike. The key for both patient and provider is to remain vigilant with glucose testing and insulin dosing post-jab to maintain glycemic control. 

In the summer of 2021, a 24-year-old woman presented to Suburban Hospital in Bethesda, Md., with rapid onset of severe diabetic ketoacidosis (DKA) and transient profound insulin resistance. Her physician, Mihail “Misha” Zilbermint, MD, MBA, FACE, associate professor of clinical medicine at the Johns Hopkins University School of Medicine and the chief and director of Endocrinology, Diabetes, and Metabolism at Suburban, ruled out every reason for the patient to have DKA, until something dawned on him, almost like around the 35-minute mark of an episode of House, MD.

“The only thing left was that she had her second COVID-19 booster shot,” Zilbermint says. “I couldn’t wait to share this with [Andrew P. Demidowich, MD] because we work so close together. I said, ‘Andrew, you’re not going to believe me,’ and he said, ‘This is probably because of the COVID-19 vaccine.’ At the time, nobody knew about it.”

Zilbermint and Demidowich published a letter to the editor in the Journal of Diabetes Science and Technology, concluding that, “although we cannot prove causality between COVID-19 vaccination and diabetic ketoacidosis, a plausible mechanism exists between the two. Therefore, it may be prudent for clinicians to warn at-risk people, such as those living with type 1 diabetes, to test their glucose more frequently and increase insulin dosing temporarily after vaccination.”

The observation at Suburban Hospital inspired Demidowich to design a clinical trial examining the impact of COVID-19 booster vaccines on glucose levels in individuals living with type 1 diabetes. The results were recently published in Diabetes Research and Clinical Practice, with the research revealing that some individuals may experience transient, mild glucose elevations after receiving a COVID-19 booster shot. This innovative pilot trial utilized blinded real-time continuous glucose monitoring (CGM) systems to assess the effects of the COVID-19 booster vaccine.

The paper comes just as the Centers for Disease Control recommended updated COVID-19  shots for everyone six months and older on September 12. “I think that this study is timely because of not only the new booster recommendations coming out, but also because we’re seeing a significant new surge of COVID infections in the community. This may encourage people to go receive the booster, who had been delaying getting the booster previously,” Demidowich says.

Comfort for Patients and Providers

For this study, Demidowich, Zilbermint, and their team enrolled 21 adult participants with type 1 diabetes to wear blinded CGMs for 10 days. After a baseline period of wearing the CGM, participants received a COVID-19 booster vaccine and had their glycemic indices measured. Two and three days after receiving the vaccine, mean glucose was significantly increased, and insulin resistance was increased on the second day.

“In addition to the paper that Misha and I wrote, there are now multiple case reports of COVID vaccines causing DKA or hyperglycemic emergencies,” Demidowich says. “However, these are still just anecdotal reports, and so, we wanted to investigate whether this is a common occurrence or a rare occurrence. We wanted to evaluate what kind of effects the booster had on glycemic control.”

The good news is that even though some of these patients experienced hyperglycemia and insulin resistance in the first few days after receiving the COVID-19 booster shot, the overall clinical effect was minimal, which is similar to findings from studies evaluating the COVID primary series. “That should give both patients and providers comfort that in most people, the COVID booster vaccine is going to be perfectly safe,” Demidowich says. “But providers and patients should have the discussion of whether to monitor glucose levels more frequently the day that you get your vaccine and for several days thereafter.”

“Best Result We Could Have Hoped For”

And again, this paper comes on the heels of the recent rollout of the updated COVID-19 vaccine and the upcoming vaccination campaign. Zilbermint points out that the CDC is shifting away from the term “booster vaccination” to “annual vaccination,” since the novel coronavirus is here to stay and will mutate over time. People living with type 1 diabetes and the physicians who treat them will need to be aware that their blood sugar may rise a few days after the vaccine, likely year after year.

Demidowich and Zilbermint note that the small size of the study was a limitation, but they point to the use of blinded real-time continuous glucose monitors – as opposed to flash glucose monitoring – as a strength since they were able to get complete 24-hour data. Another limitation was that serial inflammatory markers were not measured, which they hope to do in future studies. Although inflammation-induced insulin resistance is the main suspect driving the hyperglycemia, a number of factors could be in play.  “[I]t is unclear whether the transient glycemic elevations are directly due to inflammatory mechanisms or other factors, such as change in appetite after vaccination, decreased activity, etc.,” the authors write.

“In theory, it could be changes in physical activity,” Demidowich says. “If you feel sore and crummy after getting vaccinated, you’re not doing as much exercise or walking.  Or you might be eating or sleeping worse. So, it could be any one of those things or all them together. I think that’s a future study that’d be very interesting to pursue and evaluate.”

For now, Demidowich and Zilbermint recommend that patients at risk for hyperglycemia be aware that their glucose levels could rise after a COVID-19 vaccination, and that physicians should counsel these patients to be vigilant with glucose testing and insulin dosing for the first five days after vaccination, and be prepared to transiently increase insulin doses to maintain glycemic control.

“The study thankfully showed that the COVID vaccine does not have clinically significant effects on glucose control in most people with type 1 diabetes,” Demidowich says. “But there are the rare cases where people have a severe hyperglycemic reaction. Because of that, we think that everybody should at the very least be more cognizant and probably test more frequently on the day of vaccination and for the first several days afterwards and to review what to do in the instances of hyperglycemia with your provider. But overall, we think getting vaccinated is very safe. I think it’s almost the best result that we could have hoped for from our study.”

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