Why COVID-19 vaccine efficacy matters for older people

Data on vaccine effectiveness among seniors is lacking since many vaccine trials do not include individuals over the age of 65. For this Short Communication published in Vaccine, CITF-funded researcher Dr. Manish Sadarangani from the University of British Columbia and colleagues used mathematical modelling to assess the effectiveness of hypothetical COVID-19 vaccines that would either stop infection and transmission, or prevent severe disease.

Seniors have felt the impact of SARS-CoV-2 infections most acutely. The development of vaccines to combat SARS-CoV-2 has been a welcome innovation and has the potential to greatly reduce morbidity and mortality in populations most at risk, including seniors. As vaccines become more widely available, it will be important for them to be allocated strategically in order to have the most impact in reducing severe disease and death. This means protecting older individuals first.

In this article, the authors examined the effects of hypothetical lower efficacy vaccines among the population of British Columbia, with a focus on seniors. In their different simulations, they proposed two scenarios: a) a sterilizing vaccine that prevents infection and transmission; and b) a disease-attenuating vaccine that prevents mortality but only partially blocks transmission.

Their modelling estimated that the sterilizing vaccine would provide excellent protection to people aged 18–64, but considerable variability in protection to people aged 65 years and older. Likewise, transmission after the disease-attenuating vaccine would also be higher among people 65 years and older. The modelling suggested that even if transmission were blocked in the younger age groups, overall mortality would not be reduced if vaccines were not effectively protecting seniors. In other words, to substantially reduce mortality among people aged 65 years and over, a vaccine that protects a higher proportion of people in that group is needed.

The authors concluded that the sterilizing vaccines would be more effective in reducing infections in the general population compared to the attenuating vaccines. In both scenarios, the overall infection rate is primarily determined by the uptake of vaccination among people 18–64 years old. Prevention of mortality among seniors is strongly linked to vaccination rates among people aged 65 years and older, as well as vaccine efficacy in this group. The results show that while it is important to vaccinate the entire population and reduce the community load in order to reduce mortality among older people, ideally effective vaccines should be prioritized for use in people 65 and older. Finally, the authors recommend that people over 65 years and over should be included in future trials of COVID-19 vaccine candidates; with careful monitoring of vaccine efficacy this age group.