COVID-19 mRNA vaccines effective in real-world study of HCPs

A test-negative, case-control study demonstrated the real-world effectiveness of the BNT162b2 vaccine (Pfizer–BioNTech) and mRNA-1273 vaccine (Moderna) among healthcare personnel in the US.

“[W]e found that both the BNT162b2 and mRNA-1273 vaccines were highly effective against symptomatic COVID-19 among healthcare personnel,” said the researchers.

“Our study results showed that complete vaccination with mRNA vaccines was effective in adults with more than one risk factor for severe COVID-19; in adults with obesity, hypertension, asthma, or diabetes; and in adults [age ≥50 years],” they pointed out.

The study was conducted in 25 states in the US and enrolled participants between December 28, 2020 and May 19, 2021. Individuals who qualified as cases (n=1,482) had a positive polymerase chain reaction (PCR)* or antigen-based test for SARS-CoV-2 plus ≥1 COVID-19–like symptom. Controls (n=3,449) had a negative PCR test* for SARS-CoV-2 regardless of presence of symptoms and were week-of-test- and site-matched to cases.

Individuals with prior PCR- or antigen test-confirmed SARS-CoV-2 infection >60 days before test date were excluded. Prior to the test, 45 and 74 percent of cases and controls, respectively, had received ≥1 dose of vaccine, of whom 78 and 79 percent, respectively, received the BNT162b2 vaccine, and 21 and 20 percent, respectively, the mRNA-1273 vaccine. A total of 167 cases were detected in completely vaccinated participants and 140 cases in partially vaccinated participants.

Median age of participants was 37 years and 17 percent were male. Seventy-six percent of cases and 75 percent of controls had ≥1 underlying condition which could increase the risk of severe COVID-19. The most common conditions were obesity (36 and 31 percent of cases and controls, respectively), overweight (29 and 28 percent, respectively), asthma (14 and 18 percent, respectively), and hypertension (15 and 14 percent, respectively).

Two percent of cases were hospitalized, and 1 percent of controls were hospitalized for non-COVID-19–related illness. There were no deaths during the study. More unvaccinated than completely or partially vaccinated participants had severe symptoms or required hospitalization.

Overall, mRNA vaccine effectiveness increased from 12.8 percent 0–9 days after the first dose to 36.8 percent at 10–13 days post-first dose. [N Engl J Med 2021;doi:10.1056/NEJMoa2106599]

mRNA vaccine effectiveness after partial vaccination (14 days after first dose through 6 days after second dose) was 79.7 percent overall and was comparable between the BNT162b2 vaccine (77.6 percent) and the mRNA-1273 vaccine (88.9 percent). Following complete vaccination (≥7 days after second dose), the overall effectiveness was 90.4 percent and was also similar between the BNT162b2 and the mRNA-1273 vaccines (88.8 and 96.3 percent, respectively).

Subgroup analysis showed that the results were consistent regardless of age (<50 years and ≥50 years), race and ethnicity, presence of underlying conditions, and level of patient contact. The effectiveness was also high in pregnant women from 14 days after the first dose (77.1 percent), and potentially higher among completely vaccinated pregnant women. However, vaccine effectiveness (combining both partial and complete vaccination) was lower among participants with immunocompromised conditions (39.1 percent).

Participants were followed up for 14 weeks after the second dose. Vaccine effectiveness, assessed in 2-week intervals, was highest at 3–4 weeks after receipt of the second dose (96.3 percent).

“Estimates of vaccine effectiveness were lower during weeks 9 through 14 than during weeks 3 through 8 after receipt of the second dose, but confidence intervals overlapped widely,” noted the researchers.

Despite the lack of evidence of waning vaccine effectiveness after the second dose, the researchers acknowledged the relatively short follow-up period. “[I]t is unknown how long this level of protection from either vaccine will last, especially among persons with immunocompromising conditions or among older persons,” they said. They also recommended caution when interpreting the effectiveness of partial vaccination given “the short window of risk after the receipt of a single dose.”

“The long-term duration of protection and the effectiveness of these vaccines against emerging variants [are also] unknown and should be monitored to indicate whether changes to vaccine composition or vaccine policy are needed,” they added.

They also noted that variations in testing strategies according to study site could have affected the estimation of vaccine effectiveness.