Just last week, data from a leaked Canadian study revealed that the Moderna jab led to harmful side effects like myocarditis and pericarditis (harmful swelling of the heart) almost 2.5x as often as the Pfizer-BioNTech jab.
The news alarmed millions of Americans who received the Moderna jab, and also rattled Moderna's stock price, putting a damper on what had been a market-leading bull run.
Since then, critics of the jab have been waiting for the other shoe to drop. Now, it looks like the time has finally arrived: Two people died after receiving Moderna vaccine shots that were among lots later suspended following the discovery of contaminants, Japan's health ministry said on Saturday.
The contaminated batches were first publicized earlier in the week.
The deaths fit the profile of the typical vaccine-induced myocarditis sufferer: the side effects tend to afflict men in their 20s and 30s, Reuters reports. Their deaths occurred within days of receiving a second dose of the jab.
The men in their 30s died this month within days of receiving their second Moderna doses, the ministry said in a release. Each had a shot from one of three manufacturing lots suspended on Thursday. The causes of death are being investigated.
Japan halted the use of 1.63 million Moderna doses shipped to 863 vaccination centres nationwide, more than a week after the domestic distributor, Takeda Pharmaceutical Co, received reports of contaminants in some vials.
"At this time, we do not have any evidence that these deaths are caused by the Moderna COVID-19 vaccine," Moderna and Takeda said in a statement on Saturday. "It is important to conduct a formal investigation to determine whether there is any connection."
One public health authority asked the public not to jump to conclusions.
The government has also said no safety or efficacy issues had been identified and the suspension of the three Moderna batches was a precaution. Fumie Sakamoto, the infection control manager at St. Luke's International Hospital in Tokyo, cautioned against drawing a connection between the shots and the fatalities reported on Saturday.
"There may only be a temporal relationship between vaccination and death," Sakamoto told Reuters. "There are so many things we still don't know to make any conclusions on these two cases."
According to the Japanese government, both of the men who died had a fever the day after their second dose and died two days after getting the fever. There has been no evidence that their shots contained contaminants, a health ministry official claimed (though they were from the contaminated batches, so the fact that they died suddenly might suggest that something was off).
Then again, their deaths could simply have been caused by rare side effects, not the contaminants found in the vaccines.