“Immunity gap” revealed by changes in pathogen exposure during the pandemic
MWC researchers, in collaboration with the New Zealand Blood Service and CoRE Te Pūnaha Matatini, show reduced pathogen exposure altered New Zealanders’ immune status and susceptibility to infection at a population level. Their work challenges current thinking on immunity gaps and provides insight into future pandemic preparedness.
(Left to Right) Associate Professor Nikki Moreland, Tiaan Van Rooyen, Dr Natalie Lorenz, Aimee Paterson
New Zealand’s Covid 19 elimination strategy provided MWC researchers with a unique opportunity to investigate the effect of reduced exposure to common respiratory pathogens on immunity at a population-level.
An immunity gap study, partly funded by MWC project funding and led by Dr Nikki Moreland, Associate Professor in Immunology at the University of Auckland, looked at the effects of two years of stringent border control on SARS-CoV-2 and other respiratory pathogens.
Post-Covid, when border and travel restrictions eased, New Zealand’s health system experienced unprecedented surges in respiratory diseases, particularly Group A streptococcus (GAS) and Respiratory Syncytial Virus (RSV). A similar pattern was observed in other parts of the world.
Associate Professor Moreland and a transdisciplinary team used an immunology approach combining multiplex bead-based immunoassay technology with a longitudinal cohort analysis to understand what was driving these surges.
“The ‘immunity gap’ which describes a decline in population immunity that results from lack of pathogen exposure for non-vaccine preventable diseases is a hotly debated concept” says Nikki. “We chose to look at antibodies. Antibodies are pathogen specific molecules that circulate blood and contribute to our immune-systems memory.”
The team partnered with the New Zealand Blood Service who screened their database to identify regular long term plasma donors from March 2020 to March 2022.
Research fellow Dr Natalie Lorenz and Masters student Tiaan Van Rooyen with the help of the rest of their lab team at the University of Auckland retrieved and manually sorted around 4500 samples. They selected 150 donors with annualized samples available from March every year based on Auckland demographics.
Dr Lorenz and Tiaan set up a bead-based immunoassay with nine antigens from Group A strep, RSV, endemic corona viruses (viruses that cause the common cold) as well as SARS-CoV-2. Dr Lorenz and senior research fellow Dr Reuben McGregor analysed the samples for antigen levels against respiratory pathogens and reviewed the data. From there, Professor Alex James, a mathematician at Te Pūnaha Matatini performed further computational analysis.
Their calculations confirmed that antibodies to multiple antigens from respiratory pathogens decreased concurrently with pandemic restrictions. Paired analysis showed distinct trends supporting the emergence of an immunity gap.
“The cycle of increased immunity, through new infections, followed by waning immunity appears to have been disrupted over the time period. Only waning was observed,” says Nikki.
“On average, the geometric mean of antibodies was dropping. The average drop was between 10-16 percent over the three-year period. In contrast the SARS-CoV-2 antibodies are exponentially increasing in line with mass vaccine rollout and widespread Omicron infections in the community once borders reopened.”
Associate Professor Moreland says reduced immunity at a population level likely contributed to post pandemic surges in RSV and GAS and is an unintended consequence of the elimination strategy.
“This can inform how we better manage pandemics in the future,” she says.
Their findings were published in the Journal of Infectious Diseases1.
1 “Decline of Antibodies to Major Viral and Bacterial Respiratory Pathogens During the COVID-19 Pandemic” Journal of Infectious Diseases. The Journal of Infectious Diseases 231(1): e77-e81. https://doi.org/10.1093/infdis/jiae611