In particular, exposure to fine particulate matter (PM2.5), nitrogen dioxide (NO2) and blank carbon (BC) was associated with about a 10 per cent decrease in IgM and IgG antibody responses in people without prior infection, said researchers from the Barcelona Institute for Global Health (ISGlobal), and the Germans Trias i Pujol Research Institute (IGTP) in Spain.
The fact that previous infections lead to higher vaccine responses could explain why the effect of pollutants was only observed in people without a prior infection.
However, the role of long-term exposure to air pollution on hybrid immunity (infection plus vaccination) deserves further investigation, the researchers warned, in the study published in Environmental Health Perspectives.
"Air pollution can induce chronic inflammation, which has been associated with a negative effect on vaccine efficacy," said Carlota Dobano, researcher from ISGlobal.
"Our findings are consistent with evidence that persistent organic pollutants reduce vaccine responses in children," she added.
Air pollutants have been shown to affect immune responses. Previously it has been linked to adverse health outcomes, including lung cancer, cardiovascular and respiratory disease, and diabetes.
The team analysed data from 927 participants (aged 40 to 65 years), who answered questionnaires and gave blood samples in the summer of 2020 (right after the first lockdown) and in 2021 (after the start of Covid-19 vaccination).
All had received one or two doses of the main Covid-19 vaccines administered in Spain (made by AstraZeneca, Pfizer or Moderna).
The research team measured IgM, IgG and IgA antibodies to five viral antigens (three of them on the Spike protein contained in the vaccine). Exposure to fine particulate matter (PM2.5), black carbon (BC), nitrogen dioxide (NO2) and ozone (O3) was estimated for each participant based on his or her address before the pandemic.
The results show that in uninfected individuals, pre-pandemic exposure to PM2.5, NO2 and BC was associated with a 5 per cent to 10 per cent reduction in vaccine-induced Spike antibodies.
The decrease in antibodies was shown both for early IgM responses and late responses measured by IgG. The IgG response after the first dose peaked later in participants exposed to higher air pollution levels, and lower IgG levels persisted for several months after vaccination. Results were similar for the three vaccines.
The study did not look at whether the reduction in antibody responses led to an increased risk of breakthrough infections and their severity.
However, the findings add to the growing body of evidence on the adverse effects of air pollution even at the relatively low levels observed in Western Europe, the researchers said, while calling for stricter air pollution limits.
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