3 Epidemiology of COVID-19

Epidemiology is the “study of distribution and determinants of health-related states among specified populations and the application of that study to the control of health problems.”

The purposes of epidemiology are to:

• Discover the agent, host, and environmental factors that affect health
• Determine the relative importance of causes of illness, disability, and death
• Identify those segments of the population that have the greatest risk from specific causes of ill health
• Evaluate the effectiveness of health programs and services in improving population health

Key words in epidemiology include:

• Epidemic or outbreak: disease occurrence among a population that is in excess of what is expected in a given time and place.
• Cluster: group of cases in a specific time and place that might be more than expected.
• Endemic: disease or condition present among a population at all times.
• Incidence: the occurrence of new cases of disease or injury in a population over a specified period of time.
• Morbidity: disease, injury, or disability; any departure from a state of physiological or psychological well-being.
• Mortality: death
• Pandemic: a disease or condition that spreads across regions.
• Prevalence: number of current cases (new and existing) over a specified period of time.
• Rate: a number of cases occurring during a specific period; always dependent on the size of the population during that period.
• Vaccinated: treat with a vaccine to produce immunity against a disease. As of June 2022, everyone 6 months of age and older is eligible to receive a COVID-19 vaccination.
• Fully vaccinated: adults ages 18 and older are considered fully vaccinated 2 weeks after final dose in primary series. The primary series of COVID-19 vaccines includes 2 doses of Pfizer-BioNTech or Moderna vaccine given 3-8 weeks apart, or 1 dose of Johnson & Johnson’s Janssen vaccine.
• Booster: Booster vaccine doses are recommended for most people at least 5 months after the final dose in the primary Pfizer-BioNTech or Moderna vaccines, at least 2 months after a Johnson & Johnson primary vaccine dose.

The International Health Regulations Emergency Committee acknowledged that COVID-19 vaccination is a key tool to reduce morbidity and mortality and reinforced the importance of vaccination (primary series and booster doses, including through heterologous vaccine schedules). Three COVID-19 vaccines are used in the United States to prevent COVID-19. Pfizer-BioNTech or Moderna are COVID-19 mRNA vaccines are preferred. Johnson & Johnson’s Janssen (J&J/Janssen) COVID-19 vaccine may be given in some situations.

From: https://www.who.int/news/item/13-04-2022-statement-on-the-eleventh-meeting-of-the-international-health-regulations-(2005)-emergency-committee-regarding-the-coronavirus-disease-(covid-19)-pandemic ¹

• People Who Are Fully Vaccinated: Represents the total number of people who have received the second dose in a two-dose COVID-19 vaccine primary series or one dose of a single-dose COVID-19 vaccine primary series approved or authorized for use in the United States.²
• People Who Received a First Booster Dose: Represents the total number of fully vaccinated people who later received another dose of any COVID-19 vaccine on or after August 13, 2021. This measure does not consider how much time has passed since the recipient was vaccinated or whether the vaccine recipient is immunocompromised, has an underlying medical condition, or is at high-risk from occupational and institutional exposure to COVID-19. People who are fully vaccinated are those who received the second dose in a two-dose COVID-19 vaccine primary series or one dose of a single-dose COVID-19 vaccine primary series.

From: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/reporting-vaccinations.html ³

As of June 2022, the CDC recommends COVID-19 primary series vaccines⁴ for everyone 6 months and older, and COVID-19 boosters⁵ for everyone ages 5 years and older. People who are moderately  or severely immunocompromised⁶ have specific recommendations for COVID-19 vaccines, including boosters. People are considered to be moderately or severely immunocompromised (have a weakened immune system) due to several types of conditions and treatments. Including:

• • Been receiving active cancer treatment for tumors or cancers of the blood

  • Received an organ transplant and are taking medicine to suppress the immune system

  • Received chimeric antigen receptor (CAR)-T-cell therapy (a treatment to help your immune system attach to and kill cancer cells) or received a stem cell transplant (within the last 2 years)

  • Moderate or severe immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome)

  • Advanced or untreated HIV infection

  • Active treatment with high-dose corticosteroids or other drugs that may suppress their immune response

Individuals are up to date with your COVID-19 vaccines when they have received all doses in the primary series and one booster when eligible. Refer to the CDC’s COVID-19 booster tool⁷ to learn if and when to get boosters and stay up to date with COVID-19 vaccines.

From: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/stay-up-to-date.html⁸

As of June 2022 there have been 549 million COVID-19  cases world wide,⁹ 87.6 million cases in the United States, and 5.6 million cases in New York State, 2.6 million of which were in New York City. Trends by NYC zip code can be found here.¹⁰

As of June 2022 there have been  6.34 million COVID-19 deaths world wide,⁹ 1 million deaths in the United States,⁹ and 69,000 deaths in New York State,⁹ 41,000 of which were in New York City. Trends by NYC zip code can be found here.¹⁰

Vaccine effectiveness is a measure of how well vaccination protects people against outcomes such as infection, symptomatic illness, hospitalization, and death. COVID-19 vaccines continue to demonstrate protection against severe disease, hospitalization, and death in adults, adolescents, and children. As expected, effectiveness against infection has waned across all age groups. Protection is highest in adults who receive a booster dose. The most current relevant studies are outlined here.¹¹

The COVID-19 pandemic has brought social and racial injustice and inequity to the forefront of public health. It has highlighted that health equity is still not a reality as COVID-19 has unequally affected many racial and ethnic minority groups, putting them more at risk of getting sick and dying from COVID-19.¹² The term “racial and ethnic minority groups” includes people of color with a wide variety of backgrounds and experiences. Negative experiences are common to many people within these groups, and some social determinants of health¹³ have historically prevented them from having fair opportunities for economic, physical, and emotional health. Social determinants of health are the conditions in the places where people live, learn, work, play, and worship that affect a wide range of health risks and outcomes.

Overall, people from some racial and ethnic minority groups have less access to high-quality education. Without a high-quality education, people face greater challenges in getting jobs that offer options for minimizing exposure to COVID-19.¹⁴ People with limited job options likely have less flexibility to leave jobs that might put them at a higher risk of exposure to the virus that causes COVID-19. They often cannot afford to miss work, even if they’re sick, because they may not have paid sick days or enough money saved up for essential items like food and other important living needs.

Various strategies¹⁵ can help communities increase COVID-19 vaccine confidence and advance vaccine equity,¹⁶ but some may be particularly helpful when addressing individuals with mistrust.

• Focusing on effective messaging delivered by trusted messengers (offering recommendations provided by trusted healthcare professionals).
• Using tactics to address misinformation¹⁷ and hesitancy within the population of focus.
• Tailoring strategies¹⁸ for the specific community.
• Building vaccine confidence to help eliminate stigmas associated with receiving COVID-19 vaccination while also fostering relationships between community members and public health entities.

Addressing community concerns

According to the CDC,¹⁹ use clear, easy to read, transparent, and consistent information that addresses specific misinformation or perceived concerns, such as:

• Vaccine side effects or risk (including boosters)
• Newness and effectiveness of vaccine
• Rapidly changing information (e.g., mask use, guidance for gatherings, etc.)

Partnering with trusted messengers

Trusted messengers are key to the delivery of critical information for communities to continue advocating for positive change regarding COVID-19 vaccine efforts:

• Ensure that people whose images are included in materials and leading COVID-19 outreach efforts look like, are known to, and can effectively collect input from communities where the outreach initiatives are occurring.
• Engage trusted faith leaders or vaccine workers who share the same race/ethnicity, sexual orientation, and cultural/religious beliefs as the community to share information, promote the benefits of immunization, administer vaccines, and be present at vaccination sites.

The CDC²⁰ also recommends all material should be culturally relevant

• Arts and cultural engagement can generate community demand for COVID-19 vaccines by making vaccination an accessible and socially supported choice.
• Provide messaging and tone that is culturally relevant and in predominant languages spoken in the community.

From: https://www.cdc.gov/coronavirus/2019-ncov/community/health-equity/race-ethnicity.html²¹

Countries around the world continue to work to “flatten the curve” of the coronavirus pandemic. Flattening the curve involves reducing the number of new COVID-19 cases from one day to the next. When a country has fewer new COVID-19 cases emerging in a day than it did on a previous day, that is a sign that the country is flattening the curve.

According to Endcoronavirus.org,²² countries can be grouped into three categories in their fight against COVID-19; 1) countries that are winning the fight against the virus; 2) countries that are almost winning the fight against the virus; and 3) countries that need to take greater actions to beat the virus. The United States is among those countries that are nearly almost winning the battle.

Daily deaths is the best indicator of the progression of the pandemic, although there is generally a 17-21 day lag between infection and deaths. As the pandemic continues to recede, individuals are encouraged to continue to follow CDC guidelines²³ for vaccines and booster, quarantining if exposed, isolating if infected, following travel recommendations, and knowing when to get tested.

The pandemic has been the most consequential health crisis in a century and exposed long-standing gaps and a global under-investment in public health. In addition to the COVID death toll, issues related to poverty, health inequities, and mental health have been exposed by the pandemic. Moving forward, there is a need for health care to become more equitable, more effective, and more prepared for the next pandemic.

Experts say that in the next year, new variants are likely to be more transmissible versions of the Omicron variant. Data indicate that the existing mRNA vaccines are less than 70% effective²⁴ at preventing symptomatic COVID-19 from Omicron, even after a booster shot. As the virus further evolves, vaccines may become even less effective. Vaccine manufacturers are currently testing new formulas that are designed for Omicron and other variants. Until those become available, experts say that getting immunized and boosted with the available vaccines is the best way to protect against current and future variants.

1. https://www.who.int/news/item/13-04-2022-statement-on-the-eleventh-meeting-of-the-international-health-regulations-(2005)-emergency-committee-regarding-the-coronavirus-disease-(covid-19)-pandemic

2. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines.html?s_cid=11304:covid%20vaccine%20types:sem.ga:p:RG:GM:gen:PTN:FY21

3. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/reporting-vaccinations.html

4. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/stay-up-to-date.html#recommendations

5. https://www.cdc.gov/vaccines/covid-19/downloads/covid-19-vacc-schedule-at-a-glance-508.pdf

6. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/immuno.html

7. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/booster-shot.html?s_cid=11706:cdc%20covid%20booster%20dose:sem.ga:p:RG:GM:gen:PTN:FY22

8. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/stay-up-to-date.html

9. https://www.nytimes.com/interactive/2021/us/new-york-covid-cases.html

10. https://www1.nyc.gov/site/doh/covid/covid-19-data-totals.page

11. https://covid.cdc.gov/covid-data-tracker/#vaccine-effectiveness

12. https://www.cdc.gov/coronavirus/2019-ncov/community/health-equity/racial-ethnic-disparities/disparities-illness.html

13. https://www.cdc.gov/socialdeterminants/index.htm

14. https://www.cdc.gov/coronavirus/2019-ncov/community/health-equity/race-ethnicity.html#fn14

15. https://www.cdc.gov/vaccines/covid-19/vaccinate-with-confidence/community.html

16. https://www.cdc.gov/coronavirus/2019-ncov/community/health-equity/vaccine-equity.html

17. https://www.cdc.gov/vaccines/covid-19/health-departments/addressing-vaccine-misinformation.html

18. https://www.cdc.gov/vaccines/covid-19/hcp/tailoring-information.html

19. https://www.cdc.gov/coronavirus/2019-ncov/community/health-equity/race-ethnicity.html#fn20

20. https://www.cdc.gov/coronavirus/2019-ncov/community/health-equity/race-ethnicity.html#fn21

21. https://www.cdc.gov/coronavirus/2019-ncov/community/health-equity/race-ethnicity.html

22. https://www.endcoronavirus.org/countries

23. https://www.cdc.gov/coronavirus/2019-ncov/your-health/quarantine-isolation.html#:~:text=Stay%20home%20and%20away%20from,guidance%20for%20the%20general%20public.&text=Stay%20home%20and%20quarantine%20for,around%20others%20in%20your%20home.

24. Tenforde MW, Self WH, Gaglani M, et al. Effectiveness of mRNA Vaccination in Preventing COVID-19–Associated Invasive Mechanical Ventilation and Death — United States, March 2021–January 2022. MMWR Morb Mortal Wkly Rep 2022;71:459–465. DOI: http://dx.doi.org/10.15585/mmwr.mm7112e1