An ONS study didn’t show that the COVID-19 vaccine caused a higher risk of heart-related deaths in women, contrary to viral claim

Claims that the AstraZeneca COVID-19 vaccine increased the risk of heart-related death in young women went viral on social media in early April 2023 (examples here and here). The claim was based on a 27 March 2023 study by the U.K. Office for National Statistics (ONS) published in Nature Communications^[1] that evaluated mortality risk following COVID-19 vaccination and SARS-CoV-2 infection in young adults in England.

The study received more than 7,000 interactions on Twitter aided by prominent accounts with large followings, like “The Vigilant Fox” and political figures, including U.K. Member of Parliament Andrew Bridgen, who made false claims about COVID-19 vaccines in the past.

However, the claim that the AstraZeneca COVID-19 vaccines increased mortality in young women is unsupported by the study results. This is because the limitations of the study prevent us from establishing a causal link between vaccination and the increased risk of death, which the authors acknowledged and that we will explain below.

The ONS study didn’t demonstrate that the AstraZeneca COVID-19 vaccine caused the increase in heart-related deaths

Briefly, the ONS study estimated the risk of all-cause and heart-related death following vaccination in people aged 12 to 29 in England. To do that, the researchers used death registries from the ONS and the National Health System (NHS) Hospital Episode Statistics (HES) database to identify deaths in this population following the COVID-19 vaccine rollout on 8 December 2020 up to 25 May 2022.

Then, the authors linked death registries (3,807 from the ONS and 1,420 from the HES) to COVID-19 vaccine records from the National Immunisation Management Service and NHS Digital. The researchers estimated the risk of death following vaccination by comparing deaths that occurred during a predefined risk period of three months following vaccination with those occurring during subsequent times (control period). Since most side effects from vaccination usually show up within the first six weeks, the risk period will be more likely to cover adverse events that are truly linked to vaccination than the subsequent control period.

This type of design is called a self-controlled case series^[2]. In this type of study, the population analyzed during the risk period is also the same as its control population. This reduces the risk of bias due to confounding factors unrelated to the vaccines, such as genetics or socioeconomic status.

The study found six heart-related deaths per 100,000 young women who received a first dose of non-mRNA vaccines, mainly the AstraZeneca COVID-19 vaccine. The estimated risk was 3.5 times higher within the first three months following vaccination compared to the control period. Some social media users misinterpreted this finding as evidence that the AstraZeneca COVID-19 vaccine increased the risk of death, caused “sudden death” or as implying that COVID-19 vaccines in general aren’t safe. But this isn’t what the study showed.

Self-controlled cases series can establish correlations between the vaccine and the adverse event, in this case the risk of death. A correlation simply means that the two variables appear to be related. This association can be genuine, but it can also be coincidental or result from a confounding factor that affects the risk of death.

Therefore, while this type of design is useful to identify potential safety concerns, it’s unable to establish that the adverse events identified during the risk period were caused by the vaccine, without the help of further studies. However, many claims on social media didn’t take into account this limitation.

Another limitation is a delay in registering deaths due to coroner referrals, which are common when young people die. This delay implies that not all deaths that occurred during the control period had been registered. Therefore, deaths during this period might be undercounted.

It is important to note that the U.K. started to limit the use of the AstraZeneca COVID-19 vaccine in people under 30 in April 2021, offering this population an alternative COVID-19 vaccine instead when possible. This restriction came after reports suggesting a possible link between the vaccine and rare but life-threatening blood clots in young people. Many countries, apart from the U.K., also chose to restrict or discontinue the AstraZeneca vaccine for the same reason.

When contacted by Health Feedback regarding this claim, an ONS spokesperson highlighted the implications of this caveat in an email:

“Vaccination with the main non-mRNA vaccine in the U.K. was stopped for young people following safety concerns in April 2021. Most of those who received non-mRNA vaccines were from priority groups, such as the clinically vulnerable or healthcare workers. As such, the impact of non-mRNA vaccines cannot be generalised to the whole population.”

Vahé Nafilyan, senior ONS statistician and an author of the study, explained that this subgroup of people “was more likely to be clinically vulnerable and may be at greater risk of adverse events following vaccination than the general population”.

In other words, the ONS study didn’t demonstrate that the vaccine caused the observed increase in the risk of death. Moreover, the correlations observed in these vulnerable populations may not necessarily represent what happens in the general population.

Notably, the study didn’t find any significant increase in the risk of death in any other subpopulation. And importantly, the results didn’t show any increase in the risk of all-cause or heart-related death following mRNA vaccination.

Claims that the AstraZeneca COVID-19 vaccine increased deaths ignored the benefits of vaccination in preventing COVID-19 deaths

Any medical intervention carries some risks and COVID-19 vaccines are no exception. However, most of the side effects of COVID-19 vaccines are mild and generally last only a few days. While serious reactions to COVID-19 vaccines can occur, they are very infrequent. Furthermore, this potential risk needs to be balanced against the benefits of vaccination.

The specific populations that received the AstraZeneca COVID-19 vaccine were priority groups. Because these groups include vulnerable people who are more likely to develop severe COVID-19, they are also the ones who would benefit the most from vaccination.

In addition to the risk of death following vaccination, the ONS study estimated the risk of death following SARS-CoV-2 infection. To do that, the researchers linked death registries to national data on laboratory PCR and self-reported rapid antigen testing. The analysis only included death registries up to 31 December 2021, which was the last date the U.K. recorded COVID-19 test results.

The ONS spokesperson explained that a positive SARS-CoV-2 test result was associated with increased all-cause and heart-related mortality in the overall population. This result demonstrates that COVID-19 can pose a real health threat even in young people.

“Our analysis shows that the risk of death is greatly increased following a positive test for COVID-19 even in young people and many studies show that vaccines are highly effective at preventing hospitalisation or death following COVID-19 infection.”

More importantly, the risk was higher in unvaccinated people compared to vaccinated people (one additional death for every 12,000 and 56,000 young people, respectively).

These results strongly suggest that the benefits of mRNA COVID-19 vaccines in preventing COVID-19 deaths outweigh their potential risks. Stephen Evans, emeritus professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, said in a BMJ news article, “it is clear that infection with this virus can, rarely, lead to death in this age group, and death following vaccination is even rarer.” This means that the benefit-risk balance in non-mRNA COVID-19 vaccines might also be positive in certain circumstances, for example when the circulation of the virus is high.

Conclusion

Contrary to claims, an ONS study didn’t demonstrate that the AstraZeneca COVID-19 vaccine caused an increase in the risk of death in young women. The correlation that the authors observed could represent a genuine association or simply be coincidental or due to other factors unrelated to the vaccine. Further research on the effects of the AstraZeneca COVID-19 vaccine in young women is required in order to determine whether the association is genuine.

Furthermore, the risks of a vaccine always need to be considered in the context of its benefits. The ONS study showed a greater risk of COVID-19 death in unvaccinated people compared to vaccinated people. This result suggests that COVID-19 vaccines reduced the risk of serious COVID-19 and death.

Moreover, the ONS study also showed that mRNA COVID-19 vaccines weren’t associated with any increase in the risk of death in other populations. These results strongly suggest that mRNA COVID-19 vaccines are safe and protect against COVID-19 death also in young people.

REFERENCES

• 1 – Nafilyan et al. (2023) Risk of death following COVID-19 vaccination or positive SARS-CoV-2 test in young people in England. Nature Communications.
• 2 – Petersen et al. (2016) Self controlled case series methods: an alternative to standard epidemiological study designs. BMJ.