A communication transmitted from Louis A. DePasquale, City Manager, relative to Awaiting Report Item Number 20-48, regarding COVID-19 antibody testing

TO: Louis A. DePasquale, City Manager FROM: Claude A. Jacob, Chief Public Health Officer, Cambridge Public Health Department DATE: May 12, 2021 SUBJECT: Response to Policy Order AR 20-48, adopted September 21, 2020 Excerpt of Order: As we enter the winter months, battling both influenza and COVID-19, antibody testing for COVID-19 would be pertinent information to use as we assess our City’s strategies against COVID-19 moving forward; now therefore be it that the City Manager be and hereby is requested to confer with Claude Jacob, Chief Public Health Officer, as to the feasibility of creating such a program and report back to the City Council on this matter by October 12, 2020. During the initial surge of COVID-19 infections last spring, it was well understood in the medical community that reported cases likely reflected only a fraction of all infections, since an unknown proportion of illnesses were mild, asymptomatic, or otherwise not diagnosed. Another important confounder in the early weeks and months of the pandemic was that viral testing was limited in many states, often only available to the sickest patients or those who met narrow criteria for testing.1 Early on in the pandemic, the Centers for Disease Control and Prevention (CDC) and the scientific community became concerned that estimates of disease prevalence that relied only on case-based reporting would be confounded by these issues. National Seroprevalence Study Starting in March 2020, the CDC and scientific partners embarked on multi-state seroprevalence (antibody) surveys to better determine the “true” percentage of the U.S. population who had previously been infected with the virus (known as SARS-CoV-2).2 In July 2020, CDC expanded the seroprevalence survey to include commercial laboratories across 50 US states, Washington, DC, and Puerto Rico. The survey uses blood samples submitted to commercial laboratories for reasons unrelated to COVID-19, such as routine medical care or a sick visit. This survey aims to collect 50,000 blood samples every two weeks for a total of more than 1.2 million samples until August 2021.3 Based on data from the CDC study through September 2020, the Journal of the American Medical Association (JAMA) reported that in 42 of 49 jurisdictions (US States) with sufficient samples to estimate seroprevalence across all periods, fewer than1 0% of people had detectable SARS-CoV-2 antibodies.4 Massachusetts Findings Massachusetts sites, especially those in the eastern portion of the state, are contributing a high number of samples to the 50-state study relative to other U.S. states.5

Prior to the availability of vaccines, the CDC seroprevalence estimates for Massachusetts ranged from 4.2% (July 30-Aug. 10 sampling period) at the start of the study to 5.9% at the end of 2020 (Dec. 14-26). For the most recently published sampling period (March 8-20), the estimated seroprevalence among Massachusetts residents was 11.9%.6 Of note, at that time approximately 13% of Massachusetts residents were fully vaccinated,7which indicates that the CDC seroprevalence data was fairly on target. Cambridge Data The Cambridge Public Health Department does not have city-level seroprevalence data. However, according to local vaccination data published on May 4 by the Massachusetts Department of Public Health, approximately 62% of Cambridge residents have received at least one vaccine dose and about 38% of residents are fully vaccinated. Recommendation The Cambridge Public Health Department continues to believe that expanding Cambridge residents’ participation in antibody testing would have limited usefulness as a local public health measure at this juncture in the pandemic. The department’s rationale is as follows: • CPHD has confidence in the seroprevalence data from the CDC, which showed consistently low seroprevalence of SARS-CoV-2 antibodies in the Massachusetts population prior to the availability of vaccines. • The relatively low estimated prevalence of SARS-CoV-2 antibodies in the population prior to the vaccines indicates to CPHD that natural herd immunity is not a significant factor in ending the pandemic in the U.S. or globally. In addition, given that the duration of seroprevalence positivity is not well understood, antibody testing continues to be reserved at this time for very specific medical indications. To halt the spread of the SARS-CoV-2 virus and end the global pandemic, a high proportion of the world’s population must develop immunity to the virus, either through infection or vaccination. While the exact threshold for “herd immunity” for the virus is unknown, recent estimates from the scientific community have ranged from 70% to 90%. 8 The most expedient and effective pathway to achieving herd immunity is through vaccination. It is hoped that the vast majority of Massachusetts adults and teens will choose to get vaccinated. 1 https://www.medrxiv.org/content/10.1101/2020.06.25.20140384v1.full.pdf 2 Ibid. 3 https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/commercial-lab- surveys.html#surveymap 4 https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2773576 5Bajema KL, Wiegand RE, Cuffe K, et al. Estimated SARS-CoV-2 seroprevalence in the US as of September 2020. JAMA Intern Med. Published online November 24, 2020. doi:10.1001/jamainternmed.2020. Table 1, supplemental online content 6 CDC Nationwide Commercial Laboratory Seroprevalence Survey, accessed on March 12, 2021. 7 Massachusetts Department of Public Health. Daily Covid-19 Vaccine Report, March 15, 2021. 8 How Much Herd Immunity is Enough? New York Times, updated on March 9, 2021.