A study of adult women and infants in British Columbia, Canada demonstrated that humoral immunity against respiratory syncytial virus (RSV) was significantly reduced. Overall, the study highlights that relatively short-lived anti-RSV immunity may be responsible for the repeated seasonal resurgence of RSV infections in British Columbia. The study has just been published in the Journal of Infectious Diseases.
British Columbia, Canada saw a near-disappearance of RSV cases in the first year of the COVID-19 pandemic. Control measures put in place to mitigate the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may also be responsible for the mitigation of RSV.
Over the previous three pre-pandemic seasons (2017 to 2020), an average of 1,500 cases of RSV were detected in British Columbia. In contrast, only five cases were detected during the first pandemic season (2020-2021). This prolonged absence of RSV exposure could influence protective immune responses at the population level.
In the current study, scientists estimated binding and neutralizing anti-RSV antibody levels in women of childbearing age and infants before and during the first year of the COVID-19 pandemic.
Healthy women of childbearing age (18 to 51 years) and infants residing in British Columbia were enrolled in the study. Serum samples were collected from participants after the typical peak season for RSV infection in each year studied. Samples were used to measure anti-RSV IgG levels and neutralizing antibodies. Additionally, specific to RSV T-cell Response was measured using peripheral blood mononuclear cells.
Humoral immune responses (antibodies) to respiratory syncytial virus
Analysis of serum samples revealed that anti-RSV IgG antibody levels in females decreased significantly in 2021 compared to that seen in 2020. However, compared to antibody levels in females of the same age in 2018 and 2019, no significant difference was observed. observed.
Analysis of serum samples taken from infants revealed a 15-fold reduction in anti-RSV IgG antibody levels in 2021 compared to that observed in 2020. An inverse correlation was observed between antibody levels in infants and postnatal age (age after birth). However, no correlation was observed with gestational age (duration of pregnancy).
Neutralization of antibody responses to respiratory syncytial virus
The results of the live viral plaque test revealed that levels of anti-RSV neutralizing antibodies in women were 12 times lower in 2021 compared to those seen in 2020. A similar reduction was observed compared to levels of antibodies in 2018 and 2019. infants, a 3.4 times lower rate of neutralizing antibodies against RSV was observed in 2021 compared to that observed in 2020.
Considering all specimens collected from women and infants, a strong correlation was observed between anti-RSV IgG antibody levels and neutralizing antibody levels.
Regarding cellular immune responses, a comparable level of RSV-specific CD4+ T cell response was observed in women between 2020 and 2021.
Significance of the study
The study reveals a significant reduction in the levels of binding and neutralizing anti-RSV antibodies in women and infants after one year of the COVID-19 pandemic. In women, the reduction could be due to a prolonged absence of exposure to RSV.
Since infants are immunologically naïve to RSV, they rely primarily on maternal antibodies to avoid severe RSV infection in the first few years after birth. Thus, the reduced humoral immunity observed in infants could be due to the combined impact of waning maternal immunity and lack of exposure.
Unlike the antibody response, T cell responses in women remain mostly unchanged during the pandemic. This indicates the presence of a long-lasting memory T cell response that may protect adults against serious infections, despite a lack of humoral immunity.
However, infants who lack memory immune responses rely primarily on maternally transmitted antibodies. Thus, waning humoral immunity might make infants more susceptible to severe RSV infection.
Overall, the study indicates that anti-RSV antibody responses decline rapidly over time and that continued exposure to RSV is required for long-lasting protective immunity.
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