Fact check: Severe adverse events are rare following mRNA COVID-19 vaccines

An interview discussing COVID-19 contains a number of false claims, such as that PCR tests are unable to diagnose COVID-19, that US data shows significant “severe” reactions to mRNA vaccines, and that the 2020 death rate in Ireland was the lowest in ten years.

Reuters Fact Check. REUTERS

The video (here) contains numerous other claims and expressions of opinion, which are outside the scope of this check.


One of the speakers in the video, Prof. Dr Dolores Cahill said that she was suspicious of PCR tests used to detect SARS-CoV-2 and wanted to genetically sequence these, saying: “You would never, ever diagnose someone with just a positive PCR test or a negative. You would actually do DNA sequencing to see what is in the test. Because it’s well-known that you can just get the primers, the constituents of the tests, can give false positives. Or that if you amplify it up too much, you can actually specifically amplify up human DNA or some other type of DNA. So ,what you should be doing rigorously is in-depth forensic sequencing of the positive PCR tests, and so that wasn’t happening in the world.” (Timestamp 10.00)

Cahill did not respond to emails by Reuters requesting comment and asking for the source of this and other claims made by her.

Reuters has written about similar claims about PCR tests and sequencing made by Cahill in the past (here).

Reuters could not find credible sources to back up the claim that PCR tests should not be used to diagnose disease without sequencing each sample. “PCR testing and sequencing are totally different things,” a World Health Organisation spokesperson told Reuters by email. “It’s not that one is more accurate than the other. PCR tells you if the SARS-COV-2 virus is in a person’s body. Sequencing that virus would tell you more about the specific strain of the virus that the person had been infected with.

“Sequencing is not used for diagnosis. PCR tests are developed specifically to diagnose a disease, for example COVID-19. During the development process they are checked for specificity to be sure they do not pick up other diseases by accident.

“It would not bring any benefit to patients, who need a diagnosis, to sequence after PCR testing and it would waste time and resources. Sequencing is important for tracking variants of the virus but not for diagnosis of individuals.”

Both the Irish Health Service Executive and Public Health England told Reuters that PCR tests were a standard way of identifying infections and that both countries sequence some SARS-CoV-2 samples to monitor for variants.


Later in the video, the same speaker says of the mRNA vaccines that are approved for use against COVID-19: “In the American figures, about one in 50 people had severe adverse events within five days.” (Timestamp 56.45)

The US Centers for Disease Control (CDC) explain how they are tracking COVID-19 vaccine side effects through smartphone surveys and the Vaccine Adverse Event Reporting System (VAERS) here . A CDC update on COVID-19 vaccine safety, which looked at VAERS reports of adverse effects following vaccination received until January 18, found that the majority of adverse events were “non-serious” and that 979 serious adverse events were reported after vaccination (slide 13 here: here). It said the reporting rate for serious adverse events was 45 reports per million doses.

While not all adverse effects following vaccination may be reported, a CDC spokesperson previously told Reuters by email: “We have data to show that serious adverse events that occur after vaccination are more likely to be reported than non-serious adverse events.” Moreover, VAERS reports are designed to be an early warning system and do not confirm the reported event was indeed caused by vaccination.

The CDC said they were monitoring the safety of COVID-19 vaccines and that, while mild side-effects like pain or swelling at the injection site were common, anaphylaxis, a severe allergic reaction, was “extremely rare” (here). “Anaphylaxis after COVID-19 vaccination is rare and occurred in approximately 2 to 5 people per million vaccinated in the United States based on events reported to VAERS,” the CDC said. (here).


In the video, the host of the show also asks: “There hasn’t been excess mortality?” to which Cahill responds: “In Ireland, in 2020, it was the lowest overall death in the last ten years — of any year in the last ten years.”

The Irish Central Statistics Office (CSO) has not released official numbers relating to deaths for the entire year 2020 yet; there is a statutory time limit of three month for the registration of deaths so deaths from December may still be unrecorded (here). However, figures from the first two quarters of 2020 show an increase in deaths compared to the previous year, especially in Quarter 2 (here and here).

Preliminary estimates by the CSO say that, as of September, there were about 1,192 excess deaths in the state compared with the average of the previous 3 years. (See Table 1 Cumulative Excess Death Notices, 2020 here: here).


Partly False. Genetic sequencing is not necessary to diagnose COVID-19. VAERS data indicates that severe reactions to mRNA vaccines are rare. Annual death statistics for Ireland in 2020 have not been released yet, but figures for the first two quarters show an increase in the number of deaths.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts: here .