Covid: vaccinated older people have fewer covid hospitalizations

 The MMWR just published a report on mRNA effectiveness in older adults (see https://www.cdc.gov/mmwr/volumes/70/wr/mm7018e1.htm , or covid elderly hospitalized vaccine works MMWR2021 in dropbox)

 

Details: 

-- 417 hospitalized adults at least 65 years old from 24 hospitals in 14 states were assessed; 187 case patients who had been partially or fully vaccinated with either the Pfizer or the Moderna vaccines were compared to 230 controls, during January 1 to March 26, 2021

-- these patients were admitted with “Covid-like illness” (the presence of fever, feverishness, cough, sore throat, myalgias, shortness of breath, chest pain, loss of taste, loss of smell, respiratory congestion, increased sputum production, new oxygen saturation <94%, new requirements for invasive or noninvasive mechanical ventilation, or new pulmonary findings on chest x-ray consistent with pneumonia)

-- all patients received clinical testing for SARS-CoV-2 by PCR or antigen test within 10 days of illness onset, and they had onset of symptoms 0 to 14 days before admission

-- case patients had a positive PCR for SARS-CoV-2, controls had a negative test 

-- mean age 73 (59% were 65-74 years old, 41% at least 75yo), 38% female, 37% were non-Hispanic white, 17% non-Hispanic Black, 6% Hispanic, 4% lived in long-term care facilities

-- tobacco use in 9%, 47% received the Moderna and 53% received the Pfizer vaccine

-- electronic medical records and the state immunization registries were searched for SARS-CoV-2 vaccination for all included patients who did not have vaccination record cards to verify reported or unknown vaccination status

    -- though self-reports were accepted if patients provided vaccination dates and location

-- those receiving the J&J vaccine were not included, since very few were given that vaccine during this time period

-- models were adjusted for US census region, calendar month, age (as a continuous variable), sex, and race/ethnicity

 

Results: 

-- case patients (187 patients with covid-like symptoms and PCR positive): 19 (10%) patients had received at least one dose of the Pfizer or Moderna vaccine more than 14 days before illness onset (18 were partially vaccinated and one was fully vaccinated)

-- control patients (230 patients with covid-like symptoms but PCR negative): 62 (27%) were vaccinated (44 partially and 18 fully vaccinated )

 

-- adjusted vaccine effectiveness against Covid 19-associated hospitalizations:

    -- fully vaccinated: 94% (49%-99%)

    -- partially vaccinated: 64% (28%-82%)

-- no difference in vaccine effectiveness between the case and control patients who received the 1^st dose of a 2-dose series within 14 days before illness onset (ie, before presumed vaccine effectiveness)

 

Commentary: 

-- this study compared patients who were hospitalized, finding a dramatic decrease in outcomes (hospitalizations in this study) related to Covid in those who were not immunized. This is a standard measurement which is used for other infectious diseases, such as influenza (referred to as the “test-negative design)

-- there was only one fully vaccinated person of the 187 case patients who were hospitalized who had a positive PCR for SARS-CoV-2

-- The results of this trial are consistent with the efficacy found in the studies in the subgroup of patients at least 65 years old, and confirmed in this real-world situation

    -- this study has the advantage of looking at those who were hospitalized (the "tip of the iceberg"), confirming the general vaccine effectiveness (vs the other general population studies, where only a very small percent were that sick)

    -- on the other hand, this does highlight the issue that some fully immunized patients (0.5% of those vaccinated in this study) may be admitted to the hospital from a possible Covid infection...

-- these results are consistent with those found in Israel with the Pfizer vaccine (see covid israel mass study incl asx nejm2021 in dropbox or DOI: 10.1056/NEJMoa2101765), though this MMWR this report also included the Moderna vaccine

-- a study in 2 skilled nursing facilities in Connecticut, where frail elderly recipients received the Pfizer vaccine, also found a significant vaccine protection (see http://gmodestmedblogs.blogspot.com/2021/03/covid-pfizer-vaccine-works-well-in.html )

-- not surprisingly, there was no vaccine benefti in those who were sick within 14 days after the 1^st dose of the vaccine (ie before the vaccine would be effective). this finding makes bias less likely in the subsequent vaccine effectiveness data

 

Limitations:

-- there were still small numbers of patients in the study, leading to the large confidence intervals

-- there may be some misclassification of vaccination status or illness onset dates since some of this was self-reported

-- these patients were largely from the Northeast and South, which may limit generalizability to other areas

-- as a case-controlled study, one cannot definitively infer causality, since there could be unmeasured confounders

-- since the PCR can pick up old viral remnants for up to more than 90 days post infection, it is possible that some who were Covid-positive in fact had a non-Covid illness but their PCR remained positive (would have been great to have a viral culture or at least quantitative PCR in the fully vaccinated individual who was SARS-CoV-2 positive....)

-- there was not enough granular data assessing:

    -- the intensity of the hospitalization for the Covid infections (eg degree of dyspnea, need for ICU or more invasive management), or Covid-related meds that were needed, or length of hospitalization (ie, did the patient who was fully vaccinated have a relatively mild case? What about those partially vaccinated?  Were their cases milder than those unvaccinated?

    -- were the patients admitted solely because of the diagnosis of a Covid-like illness, or were there other factors involved in the decision to admit the patient (ie, was the patient admitted specifically because of their Covid-like symptoms or was that a less significant concern leading to admission). And criteria for admission are pretty clinician- and hospital-dependent and variable anyway

    -- for those who were partially vaccinated, when were they vaccinated? 15 days after the first shot? 5 days after the second one?  this could be important

    --were there any long-term sequelae to the patients having the covid infections in those either partially or fully vaccinated?

 

So, this study does provide reassurance that older adults vaccinated with one of the mRNA vaccines do seem to get reasonable protection, confirming other studies; and by assessing patients who were admitted to the hospital adds to the validity of this conclusion, since only a relatively small percent of those in the big efficacy trials were sick enough to be admitted to the hospital

-- the study also reinforces the importance of continued mask use, physical distancing and minimizing SARS-CoV-2 risk until at least 14 days after the 2^nd dose of the 2^nd vaccine
    --and may still be a residual risk in those fully vaccinated, in the above study found to be 0.5%, suggesting the potential utility of continued mask use in higher risk situations (eg indoors, big crowds outdoors), especially if around unvaccinated people

--and, of course, all of this again emphasizes the importance of vaccination

geoff

 

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