Covid-19 vaccines in the United States were highly effective against SARS-CoV-2 infection requiring hospitalization, ICU admission, or an emergency department or urgent care clinic visit. This vaccine effectiveness extended to populations that are disproportionately affected by SARS-CoV-2 infection.

BACKGROUND

There are limited data on the effectiveness of the vaccines against symptomatic coronavirus disease 2019 (Covid-19) currently authorized in the United States with respect to hospitalization, admission to an intensive care unit (ICU), or ambulatory care in an emergency department or urgent care clinic.

METHODS

We conducted a study involving adults (.50 years of age) with Covid-19.like illness who underwent molecular testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We assessed 41,552 admissions to 187 hospitals and 21,522 visits to 221 emergency departments or urgent care clinics during the period from January 1 through June 22, 2021, in multiple states. The patientsf vaccination status was documented in electronic health records and immunization registries. We used a testnegative design to estimate vaccine effectiveness by comparing the odds of a positive test for SARS-CoV-2 infection among vaccinated patients with those among unvaccinated patients. Vaccine effectiveness was adjusted with weights based on propensity-forvaccination scores and according to age, geographic region, calendar time (days from January 1, 2021, to the index date for each medical visit), and local virus circulation.

RESULTS

he effectiveness of full messenger RNA (mRNA) vaccination (.14 days after the second dose) was 89% (95% confidence interval [CI], 87 to 91) against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization, 90% (95% CI, 86 to 93) against infection leading to an ICU admission, and 91% (95% CI, 89 to 93) against infection leading to an emergency department or urgent care clinic visit. The effectiveness of full vaccination with respect to a Covid-19.associated hospitalization or emergency department or urgent care clinic visit was similar with the BNT162b2 and mRNA-1273 vaccines and ranged from 81% to 95% among adults 85 years of age or older, persons with chronic medical conditions, and Black or Hispanic adults. The effectiveness of the Ad26.COV2.S vaccine was 68% (95% CI, 50 to 79) against laboratoryconfirmed SARS-CoV-2 infection leading to hospitalization and 73% (95% CI, 59 to 82) against infection leading to an emergency department or urgent care clinic visit.

CONCLUSIONS

Covid-19 vaccines in the United States were highly effective against SARS-CoV-2 infection requiring hospitalization, ICU admission, or an emergency department or urgent care clinic visit. This vaccine effectiveness extended to populations that are disproportionately affected by SARS-CoV-2 infection. (Funded by the Centers for Disease Control and Prevention.)

• Effectiveness of mRNA-based vaccines was 88% against a SARS-CoV-2 infection leading to hospitalization, 90% against infection leading to ICU admission, and 91% against infection leading to an emergency department or urgent care clinic visit.
• mRNA-based vaccines were highly effective among adults who were 85 years of age or older and persons with chronic medical conditions. This finding is reassuring, given that these groups can have impaired immune responses to other vaccines.
• Effectiveness of full mRNAbased vaccination remained consistently high at least until 112 days after the second dose.
• Effectiveness of full vaccination with mRNA-1273 is very similar to that of BNT162b2 with respect to both hospital and emergency department or urgent care outcomes.
• Among adults 50 years of age or older, the effectiveness of the Ad26.COV2.S (Johnson & Johnson) vaccine was 73% with respect to a Covid-19–associated emergency department or urgent care visit and 68% with respect to Covid-19–associated hospitalization.