Inactivated and mRNA Covid-19 vaccines appear to be safe for patients treated for hypothyroidism, say researchers.

The study, to be presented at ENDO 2022, found that these vaccines do not cause significant fluctuations in thyroid function and are not associated with increased risks of emergency department visits or unscheduled hospitalisations.

"No previous studies have looked at any possible relationship between COVID-19 vaccines and unstable thyroid function control among patients receiving thyroid hormone replacement for hypothyroidism," said lead researcher David T.W. Lui from the University of Hong Kong.

"Our reassuring findings should encourage patients treated for hypothyroidism to get vaccinated against Covid-19 for protection from potentially worse Covid-19-related outcomes," Lui added.

For the study, the team evaluated an inactivated vaccine called CoronaVac and an mRNA vaccine, Pfizer BioNTech (BNT162b2) vaccine. CoronaVac uses a dead version of the SARS-CoV-2 virus. It is being used in vaccination campaigns in various countries.

Messenger RNA (mRNA) vaccines teach the body's cells how to make a protein that will trigger an immune response. The Pfizer and Moderna vaccines are mRNA vaccines.

The researchers evaluated data from more than 47,000 Covid-19 vaccine recipients taking levothyroxine for hypothyroidism.

Patients were divided into three groups: unvaccinated, those who received the CoronaVac vaccine, and those who received the mRNA vaccine.

The team found that patients who received either type of Covid-19 vaccine were not at increased risk of needing to have their levothyroxine dosage reduced or increased.