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Public Health Bulletin

Estimating past and current infections

4 September 2020, No. 300

 

Establishing past infections

Several seroprevalence studies that look at the presence of antibodies to SARS-CoV-2 in the blood serum of blood donors are taking place in the UK. The insight from these studies can help to identify the geographical areas where the prevalence is increasing and help to understand the extent to which antibodies to COVID-19 could protect people against future infection. In addition, research within specific groups and settings, such as among healthcare workers and in schools, can help to inform future policies concerning these settings and population groups.

Early findings showed that the initial spread of the infection happened more quickly among younger adults in areas like London, with infections among older people and in other areas occurring slightly later. The latest report indicates that both nationally and in London, the prevalence of antibodies is lower in the most recent weeks compared with samples taken in May. Two factors are thought to explain the difference, at least in part: waning immunity and the inclusion of donors aged over 70 in the most recent blood samples. The antibodies’ prevalence among the latter age group was found to be the lowest (2.1%) in the samples taken over the most recent four week period, which could be attributed to the fact that people over 70 were advised to self-isolate during the lockdown. SARS-CoV-2 antibody prevalence was found to be the highest among donors aged 17 to 29 (7.6%). 

Estimating current infection rates

Coronavirus (COVID-19) Infection Survey pilot involves a random sample of participants over the age of two years who are tested if they currently have the virus using self-administered throat and nose swabs, where parents or carers take swabs from younger children. The results help to understand the past and the most recent trends in COVID-19 incidence in the community.

Some of the findings from this survey were discussed in the previous Public Health bulletin. The results from the most recent report are consistent with the local picture and indicate that after the lowest point in June, the positivity rates started to increase in July and have levelled off in August. While some of the regions across England currently feature as having high incidence rates, this survey found no evidence that the differences across regions are significant. The data also indicate that there is no clear evidence that COVID-19 infection rates have changed over the most recent six-week period in any region.

COVID-19 incidence in Hackney and the City of London

COVID-19 incidence rates in City and Hackney have increased from 10 to 62 and 70 per 100,000 population in Jule, July, and August, respectively. There is a large variation in rates within Hackney with three wards, in particular - Stamford Hill West, Springfield, and Cazenove - seeing the highest rates in July and August. The rates in these wards for both months met and exceeded the threshold at which an area could be considered an area of intervention, according to the COVID-19 Contain Framework. In order to prevent the local lockdown, the Mayor of Hackney and the Director of Public Health have issued statements urging residents in these wards not to socialise with people outside their support bubble, either in their homes or in other indoor public venues.

Copyright © 2020 City & Hackney Public Health Team, All rights reserved.


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