COVID: real-world vaccine outcomes in the US

 

A recent US real-world evaluation of the 2 mRNA vaccines was just published: see https://www.cdc.gov/mmwr/volumes/70/wr/pdfs/mm7013e3-H.pdf or  covid mrna effectiveness in HCWs MMWR2021 in the dropbox

 

-- Prospective data of cohorts of health care personnel, 1^st responders, and other essential and front-line workers in 8 US locations, from December 14, 2020 to March 13, 2021. The CDC routinely tested for SARS-CoV-2  infection every week, regardless of symptom status, as well as at the onset of symptoms consistent with Covid-19

    -- Phoenix, Tucson, Miami, Duluth, Portland (Oregon), Temple (Texas), Salt Lake City

        -- of these, 53% were from the Arizona study sites

    -- participants: physicians and primary health care personnel 21%, nurses and other allied health care personnel 34%, 1^st responders 22%, other essential and front-line workers 24%

    -- 62% female, 72% aged 18 to 49, 86% white, 83% non-Hispanic, no chronic medical conditions in 69%

    -- vaccination was by either the Pfizer or the Moderna mRNA vaccines

-- 3950 people had no prior documentation of SARS-CoV-2 infection

-- 2479 (63%) received both recommended  vaccine doses, 12% received only one dose

-- participants self-collected a mid-turbinate nasal swab weekly as well as an additional nasal swab and saliva specimen at the onset of Covid-like illness

-- the results below excluded the 13 person-days between vaccine administration and partial or full immunization, because immunity was considered to be indeterminate

-- median adherence to the protocol was 100% (interquartile range 82%-100%)

 

Results:

-- SARS-CoV-2 infection was diagnosed by PCR in  205 participants (5.2% of entire group, higher in those who were male, Hispanic, 1^st responders, or living in Arizona/Florida/Texas)

-- infections were identified by weekly specimens in 58%, and at the onset of Covid like symptoms in 42%

    -- 87% of PCR-confirmed infections were associated with symptoms [though, about half of them were asymptomatic when tested, subsequently developing symptoms: ie were presymptomatic]

    -- 11% had no symptoms, remaining completely asymptomatic

    -- 2% had symptoms not considered part of their Covid definition

-- 23% of the PCR-confirmed infections were medically-attended, including 2 hospitalizations. No deaths [no breakdown as to whether these 2 hospitalized patients had vaccine or not]

 

-- unvaccinated participants: 161 cases, 1.38 SARS-CoV-2 infections per 1000 person-days confirmed by PCR (116,657 person-days)

-- fully immunized (>13 days after 2^nd dose): 3 cases, 0.04 infections per 1000 person-days, 78,902 person days

-- partially immunized: 8 cases, 0.19 infections per 1000, 41,856 person-days [5 cases in those >14 days after getting first dose only, 3 in those from >14 days after first dose to receipt of second dose]

 

-- Estimated mRNA vaccine effectiveness for prevention of infection:

    -- fully immunized: vaccine effectiveness 90% (68% - 97%)

    -- partially immunized : vaccine effectiveness 80% (59%-90%)

-- results were regardless of symptom status

 

Commentary:

-- these results are pretty phenomenal. The effectiveness in real-world vaccination, which is typically less than in the well-controlled people in the studies, pretty much equaled what was found in those controlled trials

-- this study adds to and complements the large Israeli study as well as a UK study done with routine testing

-- separate analyses in the US study above adjusted for sex, age, ethnicity, and occupation, yielding similar results

 

Limitations:

-- this was not an RCT: were those choosing to be fully vaccinated different from those electing no vaccination? Or those who skipped out on the second one?? Was there a difference in the use of personal protective mitigation strategies, leaving some more prone to infection than others???

-- participants performed their own specimen collections, subject to some variability in accuracy

-- this was a healthy subpopulation of largely younger people with few chronic medical conditions (though this paper did not detail what those chronic conditions were), potentially limiting generalizability to others

    --there is the healthy worker effect: this study involved workers, who overall are healthier than the general population

--the study took place at a time when there were likely SARS-CoV-2 variants around, but we have no information about the ambient % of the different variants in the different locations of this study, nor whether the SARS-CoV-2 infections that occurred were from variants or the regular virus

 

So,

-- a dramatic confirmation of vaccine benefit found in the efficacy trials that have been published, as well as real-world trials in the UK and Israel

-- there were so few infections (a total of 3 cases) in those who were completely vaccinated, making it clear that:

    -- both symptomatic and asymptomatic infections were prevented by the vaccine

    -- it is unlikely that the prevalent virus variants during the time of this study (up til 2 weeks ago…) escaped the vaccines (though not sufficient background data to comment with complete certainty)

 

And, another piece of great news: more than 2 dozen world leaders called for an international treaty to combat future pandemics (though pending approval by the US and China). This is what countries were saying at the beginning of Covid-19, scientists were overjoyed that they could do real science in a collaborative way (without always looking over their shoulders to see who was doing what, who was publishing more….).  but, that fell apart (trump’s xenophobia gets lots of credit for that). Finally, a sane approach to the current and future pandemics. Hope it happens…..

 

geoff

 

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