An estimated 2,000 Singaporean individuals developed severe allergic reactions from mRNA based coronavirus vaccines, according to the country's Ministry of Health (MOH). As a result of these reactions, the MOH is recommending that affected individuals not receive a second mRNA-based shot.

The reactions noted in the Ministry of Health's press release occurred in individuals that received Modena's (MRNA  ) vaccine, as well as the vaccine jointly produced by Pfizer (PFE  ) and Biontech (BNTX  ). Rather than using inactive cell matter like traditional vaccines, the two vaccines produced by the firms use messenger RNA to provide instructions to the body's immune system.

"To protect them against COVID-19, we are also evaluating and will bring in non-mRNA vaccines that are more suitable for them. We expect to do this before the end of this year after the vaccines are authorized by the Health Sciences Authority (HSA) for use in our national vaccination program. We will provide more details later when these vaccines are available."

The ministry acknowledged the growing call to accept the competing Chinese Sinovac vaccines, which had recently received a place on the World Health Organization's (WHO) Emergency Use List (EUL). The MOH responded by saying that inclusion on the EUL alone wasn't enough to warrant approval, stating, "Healthcare regulators in many developed jurisdictions, including Singapore, typically conduct further rigorous evaluations beyond WHO EUL approval before approving a vaccine for general use."

The announcement doesn't seem to have had much of an effect, if any, on stock performance. However, the steady stream of trial data and findings from vaccine distribution results will likely play a more significant role collectively from now on. Pfizer is down 0.6% after trading on Monday and Tuesday, while BioNTech is down 7.7%, and Moderna is up 2.8%.