The burden of measles and rubella has been significantly reduced due to increases in vaccination coverage globally. Progress towards measles elimination has slowed in recent years due to barriers in reaching population immunity levels of 92-95%, which is necessary to interrupt measles transmission, but it is still important to study population immunity. One survey method that can be utilized to measure immunity in populations is serological surveys. Serological surveys measure blood serum samples for pathogen antibodies to assess outbreak risk, disease burden, and inform immunization programs; however these surveys can be costly and challenging to conduct.
Sampling specimens for further testing from biorepositories storing biological samples, such as blood banks, allows researchers to conduct disease surveillance without the costs and burdens associated with collecting specimens since biorepositories are readily available in many low and middle income countries.
CEID’s Amy Winter worked with a team of researchers to exhibit how residual survey samples (blood serum samples leftover from previously conducted studies) can be used to increase serological survey feasibility. The team subsampled 9,854 residual samples from a 2016 national HIV survey and tested the samples for rubella and measles antibodies to identify immunity gaps in the Northern, Muchinga, Eastern, Central, Luapula, Copperbelt, Lusaka, Southern, Northwestern, and Western provinces of Zambia.
The seroprevalence of measles in Zambia was 82.8% for individuals younger than 50, and measles seroprevalence (immunity) increased with age. Females had significantly higher measles seroprevalence relative to the males sampled, and the seroprevalence was 71% for the 0-4 age group, 82% for the 5-9 age group, 82% for the 10-14 age group, 87% for the 15-19 age group, and 88% for the 20-49 age group. At the time that these serum samples were collected in 2016, there was a high risk of a measles outbreak in Zambia, and the national Zambian seroprevalence was 78.3%, which is below the 92-95% seroprevalence necessary to interrupt measles transmission. Immunity varies greatly between provinces, from 78.2% in Luapula to 87% seroprevalence in Northern.
The seroprevalence of rubella in Zambia was 74.9% for individuals younger than 50, and there was seroprevalence variation across the provinces, ranging from 70.1% in Central Province to 78.9% in Lusaka Province. Similar to measles, rubella seroprevalence increased with age. The seroprevalence was 27.3% for the 0-4 age group, 65.1% for the 5-9 age group, 82.3% for the 10-14 age group, 91.2% for the 15-19 age group, and 95.7% for the 20-49 age group, but there was no significant difference in rubella seroprevalence between genders.
This research highlights the value of biorepositories to inform vaccination strategies, measure disease burden, evaluate vaccination programs, and track progress towards reaching population immunity levels. The research team plans to build upon these findings to develop predictive models of district seroprevalence in Zambia.
Click here for more information.
By: Brenna Daly