Computational study didn’t demonstrate that COVID-19 vaccine boosters increase mortality in care homes

Ten months after the beginning of the COVID-19 pandemic in 2020, the U.K. became the first country in the world to authorize and administer COVID-19 vaccines to its population. In September 2021, the U.K. began to recommend COVID-19 booster shots after evidence emerged showing that vaccine-induced immunity waned over time.

Booster shots bolster both infection-induced and vaccine-induced immunity against COVID-19 and provide updated protection against new SARS-CoV-2 variants. The U.K. now organizes regular COVID-19 booster vaccination campaigns to protect vulnerable people, such as the elderly.

COVID-19 vaccines are generally credited with saving lives. The World Health Organization (WHO) reported that COVID-19 vaccination saved more than 1.4 million lives across Europe as of January 2024, adding that “the first vaccine booster alone saved 700 000 lives”.

In contrast, the website The People’s Voice claimed that “COVID-19 mRNA boosters directly contributed to the deaths of millions of nursing home residents worldwide”. It added that “vaccinating care home staff appeared to have a consistently negative impact on resident mortality” and concluded by affirming that there was “no strong evidence supporting continued vaccination of residents or staff”.

The People’s Voice has a track record of publishing false claims about COVID-19, some of which were refuted by Science Feedback in earlier reviews.

In this instance, the website based its claim on a “major new peer-reviewed study” published in 2024 in European Economic Review by Sourafel Girma and David Paton, two industrial economists^[1].

Girma’s research focuses on “firm level adjustment to the process of globalisation and international industrial organisation”, while Paton’s research expertise is in the economics of cricket, teenage pregnancy, gambling taxation, and post-Brexit economy. Neither hold credentials in epidemiology, immunology, or medicine.

In its article, The People’s Voice misrepresented and exaggerated the findings of the study by Paton and Girma, as we will show below.

What did the study do?

The study evaluated how changes in vaccine coverage in care homes from different administrative regions in the U.K. impacted mortality among elderly care home residents.

To do so, they implemented a computational model estimating how various factors other than vaccination (confounding variables) influenced the likelihood of being vaccinated or dying, from COVID-19 specifically or from any cause. Accounting for confounding variables is crucial to make sure a change in mortality is only due to changes in vaccination, and not to some other factor.

Confounders taken into consideration included population density in different UK regions, public health expenditure, age of care home residents, and local SARS-CoV-2 infection rates.

Once they corrected for these confounders, they found that vaccination of care home residents was associated with lower COVID-19 mortality and all-cause mortality in the weeks following vaccination (Table 5 of Girma and Paton).

The results changed when the authors split the data between the period when people received their first two doses of vaccine (primary series) and the period when people started getting booster vaccines.

Indeed, the results still showed a reduction in COVID-19 cases and all-cause mortality in the weeks following primary series vaccination (Table 6a of Girma and Paton’s study). By contrast, there was no reduction in mortality in the weeks after the booster (Table 6b of Girma and Paton’s study). On the contrary, the study reported a slight, but statistically significant, increase in COVID-19 mortality and all-cause mortality four to six weeks following booster vaccination.

The authors also correlated vaccine coverage in care home staff with the residents’ mortality. They observed an association between staff vaccination and a higher resident COVID-19 mortality zero to six weeks following the primary vaccination. Staff vaccination was also associated with a higher resident mortality from zero to four weeks following booster vaccination.

The study didn’t demonstrate that staff vaccination increased the residents’ mortality

The People’s Voice claimed that “vaccinating care home staff appeared to have a consistently negative impact on resident mortality”, suggesting that there was a causal relationship between staff vaccination and the deaths of residents.

However, the authors didn’t establish that the relationship was causal. Indeed, they wrote: “[T]he fact that we observe that effect even when using early lags (i.e. before a vaccination effect could be observed), suggests this may not be a true causal effect”.

In other words, the effects of vaccination take time to appear, usually a couple of weeks. It’s thus implausible that vaccinating the staff had any impact, positive or negative, on the residents’ health at the time of vaccination or shortly after. Therefore, the observed association is likely to be due to bias or artifacts in the data.

Furthermore, the association between staff vaccination and resident mortality depended on the choice of some of the model parameters. Namely, the authors observed this association when they applied to the model the assumption that vaccine effectiveness waned at a rate of 3% per week, based on UK Health Security Agency vaccine surveillance reports. However, when they changed the rate of waning to 4% per week, the association disappeared (Table A7b in the supplementary data of Girma and Paton’s study).

This is important because if the association was strong and independent, it would persist even when some of the model’s parameters were slightly modified. Yet this wasn’t the case. This observation supports the authors’ conclusion that the association between staff vaccination and resident mortality isn’t causal, contrary to the claim by The People’s Voice.

The study didn’t demonstrate that booster doses caused residents’ deaths

The People’s Voice also suggested that the study proved the association between booster vaccination in residents and resident mortality was causal. However, Girma and Paton were more cautious about their results since the case isn’t strong enough to conclude that there is a causal link. Indeed, several limitations weaken the case for a causal relationship.

First, neither the authors nor The People’s Voice provided a plausible biological mechanism as to why the first two doses of COVID-19 vaccines would reduce mortality, while the third one would increase it.

Second, the authors didn’t directly compare residents who received a booster with those who didn’t. Rather, they observed that administrative regions where the rate of booster vaccination was higher were associated with a higher mortality of residents, once all other confounding variables were taken into account. Thus, the study doesn’t tell us whether residents who didn’t receive boosters at all died from COVID-19 or from any other cause at a higher rate than residents who received a booster. Not having that piece of information further weakens the case for a causal link between boosters and death.

Finally, the study used population-level data, not individual health records. Without individual records, we don’t have information on the vaccination status of each resident who died, and therefore can’t determine whether vaccinated residents made up the majority of the residents who died.

Individual-level data on vaccination status would be needed to demonstrate whether there was an association between booster vaccination and mortality, but the study didn’t include such data. By contrast, many other studies did include individual-level data and found that boosters reduced mortality, as we’ll discuss in the next section.

All these limitations together indicate that the causal link between COVID-19 boosters and mortality from COVID-19 claimed by The People’s Voice isn’t convincingly established by Girma and Paton’s study.

 

Other available studies contradict the claim and show that COVID-19 boosters reduced mortality

Many other studies investigated the effectiveness of COVID-19 vaccines and boosters against COVID-19 mortality. These studies generally used statistical approaches that differed from those used by Girma and Paton.

They relied on individual-level data, where the vaccination status of people who died was known. This isn’t to say that one approach is superior to the other, but that those individual-level studies provided another type of information that wasn’t mentioned in The People’s Voice article.

One observational study on more than 170,000 care homes residents in Australia found that the booster effectiveness against COVID-19 mortality ranged from 56% to 83%. In other words, boosters reduced COVID-19 mortality in those who received them^[2].

A study on more than 13,000 long term care facilities in England found that boosters (the third, fourth, and fifth doses of vaccine) reduced the risk of COVID-19 deaths^[3].

A study on more than 15 million people living in the Netherlands found that booster effectiveness against COVID-19 deaths was above 80% among residents of long-term care homes^[4].

The U.S. Centers for Diseases Control and Prevention (CDC) published a study reporting a high vaccine effectiveness (89%) against COVID-19 mortality among nursing home residents in the U.S.^[5]

And a study from Israel showed that COVID-19 mortality was lower among people aged 50 and older who received a booster compared to those who hadn’t^[6].

Altogether, results from multiple published studies don’t support the hypothesis that booster doses increase mortality risk, directly contradicting The People’s Voice’s claim.

Conclusion

The People’s Voice misrepresented the conclusions of a study by Girma and Paton on COVID-19 vaccination and mortality among U.K. nursing home residents. The study found that the first two vaccine doses moderately reduced mortality.

While the authors did observe an association between booster doses and increased mortality, they did not conclude that the link was causal, as The People’s Voice suggested. The absence of a plausible biological mechanism, lack of data on the vaccination status of deceased residents, and potential biases all weaken the case for a causal relationship. Moreover, numerous other studies from different countries have consistently shown that care home residents who received boosters had a lower risk of death compared to those who didn’t.

REFERENCES

• 1 – Girma & Paton (2024) Using double-debiased machine learning to estimate the impact of Covid-19 vaccination on mortality and staff absences in elderly care homes. European Economic Review.
• 2 – Liu et al. (2023) Effectiveness of COVID-19 vaccination against COVID-19 specific and all-cause mortality in older Australians: a population based study. The Lancet Regional Health Western Pacific
• 3 – Stirrup et al. (2023) Effectiveness of successive booster vaccine doses against SARS-CoV-2 related mortality in residents of long-term care facilities in the VIVALDI study. Age and Ageing.
• 4 – de Gier et al. (2023) Effect of COVID-19 vaccination on mortality by COVID-19 and on mortality by other causes, the Netherlands, January 2021–January 2022. Vaccine.
• 5 – McConeghy et al. (2022) Effectiveness of a Second COVID-19 Vaccine Booster Dose Against Infection, Hospitalization, or Death Among Nursing Home Residents — 19 States, March 29–July 25, 2022. Morbidity and Mortality Weekly Report.
• 6 – Arbel et al. (2021) BNT162b2 Vaccine Booster and Mortality Due to Covid-19. The New England Journal of Medicine.