COVID-19 vaccines highly effective against hospitalization, ICU admission

Stephen Padilla
14 Sep 2021

A US study has found that COVID-19 vaccines are very effective at preventing SARS-CoV-2 infection requiring hospitalization, intensive care unit (ICU) admission, or an emergency department (ED) or urgent care clinic visit among adults aged 50 years, including those most at risk for severe disease due to advanced age, comorbidities, or race/ethnicity.

“These findings reinforce the value of widespread COVID-19 vaccination, underscore the importance of completing vaccination for both mRNA-based vaccines, and may help to motivate persons who remain hesitant to be vaccinated, including Black adults and Hispanic adults,” the researchers said.

“Early findings suggest that the Ad26.COV2.S vaccine also has high effectiveness, although additional data are needed,” they added.

Adults with COVID-19–like illness who underwent molecular testing for SARS-CoV-2 were included in the analysis. The researchers examined 41,552 admissions to 187 hospitals and 21,522 visits to 221 EDs or urgent care clinics from 1 January to 22 June 2021 in multiple sites. The patients’ vaccination status was documented in electronic health records and immunization registries.

A test-negative design was used to estimate vaccine effectiveness by comparing the odds of a positive test for SARS-CoV-2 infections among vaccinated patients with those among unvaccinated ones. Vaccine effectiveness was adjusted with weights based on propensity-for-vaccination scores and according to age, geographic region, calendar time (days from 1 January 2021 to the index date for each medical visit), and local virus circulation.

Full mRNA vaccination (≥14 days after the second dose) demonstrated effectiveness of 89 percent (95 percent confidence interval [CI], 87–91) against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization, 90 percent (95 percent CI, 85–93) against infection leading to an ICU admission, and 91 percent (95 percent CI, 89–93) against infections leading to an ED or urgent care clinic visit. [N Engl J Med 2021;doi:10.1056/NEJMoa2110362]

In terms of a COVID-19–related hospitalization or ED or urgent care clinic visit, the effectiveness of full vaccination was comparable with the BNT162b2 and mRNA-1273 vaccines (range, 81 percent to 95 percent) among adults aged 85 years, persons with chronic medical conditions, and Black or Hispanic adults.

“This study complements other published estimates of the effectiveness of the BNT162b2 vaccine, and it confirms that the effectiveness of full vaccination with mRNA-1273 is very similar to that of BNT162b2 with respect to both hospital and ED or urgent care outcomes,” the researchers said. [Lancet 2021;397:1725-1735; N Engl J Med 2021;384:1412-142; Lancet 2021;397:875-877; BMJ 2021;373:n1088-n1088]

Furthermore, the effectiveness of the Ad26.COV2.S vaccine was 68 percent (95 percent CI, 50–79) against laboratory-confirmed SARS-CoV-2 infection requiring hospitalization and 73 percent (95 percent CI, 59–82) against infection resulting in an ED or urgent care clinic visit.

On the other hand, the effectiveness of one-dose mRNA-based vaccination (≥14 days after the first dose but before the second dose) was 54 percent against infection leading to hospitalization and 68 percent against infection warranting ED or urgent care clinic visits.

“These vaccine-effectiveness point estimates, and in particular the partial (one-dose) effectiveness of the BNT162b2 vaccine, should be interpreted with caution, given the heterogeneity in estimates among partners and because vaccine-effectiveness estimates are probably dependent on the observation period,” the researchers said.

“Nonetheless, during our study period, the effectiveness of full two-dose mRNA-based vaccination was consistently higher than the effectiveness of partial (one-dose) vaccination; this finding reinforces the importance of completing vaccination with both doses of mRNA-based vaccines,” they added.

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