A summary of presentations from the weekly Summit partner webinars

February 10, 2022 – The latest Summit summary

Effectiveness of a Third mRNA Vaccine Against COVID-19-Associated Emergency Department or Urgent Care Encounters and Hospitalizations among Adults, August 2021 to January 2022, VISION Network – Mark Thompson (CDC)

Mark Thompson, Ph.D., Lead, High Risk and Electronic Cohorts Team, EPI Task Force, CDC COVID-19 Response, CDC, gave a presentation on CDC’s MMWR: Effectiveness of a Third Dose of mRNA Vaccines against COVID-19–Associated Emergency Department and Urgent Care Encounters and Hospitalizations among Adults during Periods of Delta and Omicron Variant Predominance—Vision Network, 10 States, August 2021–January 2022 (1/28/22).

This study looked at the VISION network of eight integrated healthcare and research centers in ten states, including 383 emergency departments (ED) and urgent care clinics (UC), as well as 259 hospitals. The research was built on a previous flu vaccine effectiveness (VE) research infrastructure with previously published methods. (https://www.nejm.org/doi/full/10.1056/nejmoa2110362)


The study looked at adult patients age ≥18 years presenting with COVID-19-like illness.  Included patients were tested for SARS-CoV-2 by PCR.  A positive SARS-CoV-2 test within 14 days or 72 hours after admission/encounter was needed to be considered a SARS-CoV-2 cases for this study. The study excluded those with 1 or >3 doses of the vaccine, those 1–13 days since dose two or three, and individuals who got the Janssen (Johnson & Johnson) vaccine.

The start date was August 26, 2021 (14 days after CDC first recommended booster doses). The end date was January 5, 2022.


A fuller description of the study results can be found at the link above.  Overall, VE against ED or UC encounters was lower against Omicron and waned more after 180 days from vaccination when compared to the Delta variant among fully vaccinated people.  However, booster doses significantly improved VE against both variants.   In addition, VE was higher against hospitalization compared to ED/UC visits and the VE against hospitalization was also improved after booster vaccination.


Vaccine effectiveness was lower when the Omicron variant became predominant and VE declined over time.  However, VE was largely restored by booster vaccination.   The VE was significantly lower among those who received their second dose of an mRNA vaccine ≥180 days earlier and increased following the third dose. The vaccines were more effective in preventing COVID-19-associated hospitalizations than against ED/UC visits and immunocompromised individuals had lover VE for all doses, with VE being highest following their third primary dose.

Further findings from MMWR Early Release:

Waning 2-Dose and 3-Dose Effectiveness of mRNA Vaccines against COVID-19–Associated Emergency Department and Urgent Care Encounters and Hospitalizations among Adults during Periods of Delta and Omicron Variant Predominance—Vision Network, 10 States, August 2021–January 2022 (2/11/22)

mRNA VE against COVID-19 ED/UC Delta Predominance 

The study looked at VE comparing unvaccinated individuals with  fully vaccinated individuals, and fully vaccinated individuals with three doses (booster vs additional dose for immunocompromised persons was not assessed).Per the MMWR cited above “Vaccine effectiveness (VE) against COVID-19–associated emergency department/urgent care (ED/UC) visits and hospitalizations was higher after the third dose than after the second dose but waned with time since vaccination. During the Omicron-predominant period, VE against COVID-19–associated ED/UC visits and hospitalizations was 87% and 91%, respectively, during the 2 months after a third dose and decreased to 66% and 78% by the fourth month after a third dose. Protection against hospitalizations exceeded that against ED/UC visits.”



After the third dose it looks like your immunity drops as quickly as if you only had two doses. In the new data, at 199 days VE is 81% with two doses and 84% with the third and seems to be dropping at the same pace. Why is there an equally rapid decline even after the third dose?

Mark Thompson

When the immune system gets hit with the same antigen many times, antibody levels tend to peak at lower levels and antibody titers wane faster.


The flu has a very short incubation period, similar to Omicron variant. A longer incubation period allows immune cells more time to ramp up based on prior exposure or vaccination and will the body more time to mount an immune response.  How much might the shortening incubation period be contributing to the lower vaccine effectiveness we are seeing?


There is no information about the impact of the shortened incubation period on vaccine effectiveness.


Given the waning effectiveness against hospitalizations that your study found, are there any efforts to look at death rates, as well?

Mark Thompson

We are hesitant to use VISION data for estimating vaccine effectiveness against death because of so many confounders.



1. The NAIIS Annual meeting will be split into two segments The NAIIS Flu Day will be virtual this year. The tentative day for the virtual flu session is May 19 from 2:00–4:30 p.m. (ET). The adult vaccination component will hopefully be in person, COVID-19 permitting, in September or October 2022.

2. Immunize​.org has introduced a new patient handout to assist providers with influenza vaccination uptake: Not Sure If You Can Get an Influenza Vaccine? This handout, ideally printed as a two-sided, single page, addresses a variety of concerns (e.g., egg allergy, history of Guillain-Barre syndrome, pregnancy, and a weakened immune system). Immunize.org has also recently introduced How to Administer Multiple Intramuscular Vaccines to Adults During One Visit co-administration handout for healthcare workers.

3. We would welcome having even more NAIIS member organizations to add their support to the Call to Action on adult immunization. Access the call to action and click on the top righthand button to add your organization.

4. If you are not getting NAIIS emails, please add info@izsummitpartners.org (sender: NAIIS) to your list of email contacts to keep receiving the NAIIS emails.

5. There is new zoom login information this year. Please check your emails with the call agendas from NAIIS for the new zoom link and password information.

6. Immunize.org hosted two influenza webinars in September that can now be viewed online.

7. Immunize.org, with funding support from CDC and Seqirus, is offering a limited quantity of FREE Flu vaccine and COVID-19 vaccine buttons and stickers. To receive these supplies at no cost, please order now:

Order the free flu buttons and stickers (in Spanish).

Order the free COVID-19 buttons and stickers (in English and Spanish).


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