Understanding the immunity gap for serogroup B invasive meningococcal disease due to non-pharmaceutical interventions during the Covid-19 pandemic.

BACKGROUND/

OBJECTIVES

Cases of Invasive Meningococcal Disease (IMD) dropped sharply due to non-pharmaceutical interventions during the Covid-19 pandemic, raising the possibility of a disease rebound due to an immunity gap. This has been investigated via a seroprevalence study of individuals less than 25 years old, by measuring meningococcal serogroup B (MenB) serum bactericidal antibody (SBA) titres in sera collected during 2019, 2020 and 2021. SBA titres in vaccine-eligible populations since the introduction of 4CMenB were also evaluated via comparison with data obtained before vaccine introduction.

METHODS

Serum samples were obtained from the United Kingdom Health Security Agency (UKHSA) Seroepidemiology Unit (SEU) and stratified by age. 1656 samples were requested of which 1586 samples were available. Functional antibody levels were analysed using a standardised, validated SBA assay against serogroup B strain NZ 98/254 (B: P1.7-2,4: ST-42 (cc41/44)). Samples were excluded if they were insufficient, did not obtain a titre or showed evidence of non-complement mediated lysis.

RESULTS

1371 valid titres were obtained. There was a significant decrease in the proportion of individuals (all ages) with a positive titre (≥4) between 2019 and 2021. For 2019, 2020 and 2021, SBA geometric mean titres (GMTs) in infants aged 6 to 24 months were significantly higher than GMTs obtained between 2001 and 2004.

CONCLUSIONS

Disruption caused by the Covid-19 pandemic has resulted in a significant decrease in antibody levels, most likely due to reduced exposure to circulating meningococci being carried asymptomatically in the nasopharynx. Disruption to the routine immunisation schedule is unlikely to be a contributory factor as vaccine coverage was not significantly affected during the epidemiological year 2020 to 2021. Routine immunisation of infants has resulted in a significant increase in SBA GMTs in infants aged 6 to 24 months, compared to an age-matched population prior to the vaccine introduction.