During the throes of the COVID-19 pandemic, the elderly were identified as some of the most vulnerable among us as their weaker immune systems and underlying health issues made them particularly prone to hospitalisation. As a result, seniors were given priority for the anxiously awaited vaccine rollout, but questions lingered about how much protection vaccines afford the elderly.
“All the first [clinical] trials for the Pfizer and Moderna vaccines were done in 18- to 50-year-olds,” explained Laurent Rénia, a Senior Fellow and Principal Investigator at the A*STAR Infectious Diseases Labs (ID Labs). “Since the over 60s group were the most affected by COVID-19, it was essential to generate data for this population.”
In a cooperative venture with scientists at A*STAR’s Singapore Immunology Network (SIgN), the National Centre for Infectious Diseases, Singapore, and the Duke-NUS Medical School, Rénia’s team aimed to connect the dots between age and COVID-19 vaccine effectiveness. They recruited over 300 Singaporean volunteers of different ages, all of whom had been vaccinated with two doses of the Pfizer/BioNTech vaccine, to participate in their study.
The researchers looked at various aspects of the immune response to vaccination, including antibody production, T cell and memory B cell responses. They also tested how well the vaccine worked against different variants, including the original SARS-CoV-2 strain, the Delta variant and the Omicron variant.
Their findings indicated that two vaccine doses were usually enough to generate robust immune responses against the original virus isolate across the entire cohort, but this regimen was less effective against the Delta and Omicron variants. However, after stratifying for age, the team observed that individuals over 60 showed weaker antibody responses to vaccines than those in the younger age groups.
Rénia explained, “Ageing is associated with a decrease in cellular and humoral immune responses, which is in large part due to inflammation,” adding that chronic low-grade inflammation is known to dampen B cell activity, which may explain the diminished antibody production.
On a positive note, a third booster shot greatly improved the immunity of older individuals against all variants, which the team found stimulated both B and T cell responses as well as antibody production. This important finding formed part of the basis for the Singapore Ministry of Health’s recommendation of a third vaccine dose to protect the elderly and immunocompromised individuals.
Finally, the researchers reported that after six months, the vaccine's effectiveness waned in about a third of the volunteers, regardless of age. Rénia said that in these cases, second-generation vaccines can help overcome this ‘vaccine fatigue’ and offer longer-lasting immune protection, an area of research that the team is currently exploring.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Infectious Diseases Labs (ID Labs).
