Studies: COVID vaccines effective, with limited waning

A trio of new studies yesterday in the New England Journal of Medicine report encouraging results on the effectiveness and durability of protection of COVID-19 vaccines against hospitalization and death, including teens.

98% protection against ICU stay, life support

One study, led by the Centers for Disease Control and Prevention's (CDC's) COVID-19 Response Team, involved 445 hospitalized COVID-19 patients 12 to 18 years old and 777 uninfected matched controls at 31 hospitals in 23 states from Jul 1 to Oct 25, 2021, after the emergence of the Delta (B1617.2) variant. Seventeen case patients (4%) and 282 controls (36%) had received two doses of the Pfizer/BioNTech COVID-19 vaccine.

Among case patients, 180 (40%) were admitted to an intensive care unit (ICU), and 127 (29%) needed life support. Of all ICU patients, only two were fully vaccinated. Overall vaccine effectiveness (VE) against hospitalization was 94% (95% confidence interval [CI], 90 to 96).

Among uninfected controls with COVID-like symptoms, VE was 95% (95% CI, 91 to 97), while it was 94% (95% CI, 89 to 96) among uninfected controls with no symptoms. VE was 98% against ICU admission and 98% against requiring life support. Seven patients died, and 13 required extracorporeal membrane oxygen, all of whom were unvaccinated.

Three-quarters of the COVID-19 patients had underlying chronic illnesses, and nearly half were Black or Hispanic (24% and 25%, respectively).

On Oct 22, the researchers published interim findings from the study showing 93% VE for the Pfizer vaccine against COVID-related hospitalization among 179 12- to 18-year-old case patients at 19 sites in 16 states.

Of the current study, the authors said, "In this real-world evaluation of the effectiveness of the BNT162b2 mRNA vaccine in adolescents between 12 and 18 years of age in the United States, when the delta variant was predominant, we found that the vaccine was highly effective against Covid-19 hospitalization and critical illness, including among patients with underlying risk factors for severe illness. Vaccination averted nearly all life-threatening Covid-19 illness in this age group."

In a related editorial, Kathryn Edwards, MD, of Vanderbilt University Medical Center, noted that as of Dec 1, only 15% of US children aged 5 to 11 years had received at least one COVID-19 vaccine dose, a figure that contrasts sharply to the 95% vaccine uptake of routine pediatric vaccines. By Dec 23, more than 7.5 million US children had been infected, and 721 had died, she added.

"Vigorous efforts must be expended to improve vaccination coverage among all children and especially among those at highest risk for severe COVID-19," Edwards wrote. "The highly effective surveillance network that is described in this study must also continue to monitor hospitalization data over time to assess waning of immunity, protection against new variants of concern (particularly the rapidly spreading B.1.1.529 [omicron] variant), and the need for and timing of additional vaccine doses."

VE against hospitalization fell to 80%, 92% at 5 months

A study led by United Kingdom Health Security Agency researchers assessed the effectiveness of the Pfizer and AstraZeneca vaccines among COVID-19 patients in England from Dec 8, 2020, to Oct 1, 2021, a period marked by the emergence of Delta.

Of 7,106,982 COVID-19 polymerase chain reaction (PCR) test results within 10 days of symptom onset, 6,056,673 were linked to the National Immunisation Management System. A total of 1,706,743 people tested positive for COVID-19 during the study period, of whom 544,468 were infected with the Alpha (B117) variant, 1,125,257 were infected with the Delta variant, and 37,018 had another or unknown variant.

The researchers also assessed 4,349,930 negative tests from 3,763,690 participants, of whom 510,177 had two negative results, and 76,063 had three negative results more than 7 days after a previous negative test.

Overall, 2,376,037 participants (39.2%) had received two doses of the AstraZeneca vaccine, and 2,133,769 (35.2%) had received two doses of the Pfizer vaccine. A total of 22,575 participants were hospitalized with COVID-19 within 14 days after the test, and 6,336 died within 28 days.

VE against symptomatic disease caused by the Delta variant peaked in the early weeks after the second dose, then declined by 20 weeks to 44.3% (95% CI, 43.2 to 45.4) for AstraZeneca and 66.3% (95% CI, 65.7 to 66.9) for Pfizer.

Waning VE against infection with symptoms was greater in patients 65 years and older than in those 40 to 64. VE against hospitalization with infection with the Delta variant was 80.0% (95% CI, 76.8 to 82.7) with AstraZeneca and 91.7% (95% CI, 90.2 to 93.0) with Pfizer 20 weeks or more after vaccination. Similarly, VE against death due to the Delta variant for the AstraZeneca vaccine was 84.8% (95% CI, 76.2 to 90.3) and 91.9% for Pfizer (95% CI, 88.5 to 94.3).

"Our data provide evidence of waning of protection against symptomatic infection after the receipt of two doses of the [AstraZeneca] or [Pfizer] vaccine from 10 weeks after receipt of the second dose," the study authors wrote. "Protection against hospitalization and death, however, was sustained at high levels for at least 20 weeks after receipt of the second dose."

Pfizer, Moderna fared better than J&J

An observational study led by University of North Carolina at Chapel Hill (NCCH) researchers involved mining data on COVID-related outcomes and vaccination with the Pfizer, Moderna, and Johnson & Johnson (J&J) vaccines from Dec 11, 2020, to Sep 8, 2021, for about 10.6 million state residents.

Two months after receipt of the first Pfizer or Moderna COVID-19 vaccine dose, estimated VE against symptomatic or asymptomatic infection was 94.5% (95% CI, 94.1 to 94.9) and 95.9% (95% CI, 95.5 to 96.2), respectively, declining to 66.6% (95% CI, 65.2 to 67.8) and 80.3% (95% CI, 79.3 to 81.2), respectively, by 7 months.

Estimated VE among patients who received the Pfizer or Moderna vaccine early fell by roughly 15 and 10 percentage points, respectively, from mid-June to mid-July, when the Delta variant became dominant.

Among recipients of the one-dose J&J vaccine, VE against infection was 74.8% (95% CI, 72.5 to 76.9) at 1 month, dropping to 59.4% (95% CI, 57.2 to 61.5) at 5 months.

VE against hospitalization or death after two doses of the Pfizer vaccine peaked at 96.4% (95% CI, 95.1 to 97.4) at 2 months and was still at 88.7% (95% CI, 86.9 to 90.3) at 7 months. Moderna two-dose effectiveness peaked at 97.2% (95% CI, 96.1 to 98.0) at 2 months and was still 94.1% (95% CI, 92.7 to 95.2) at 7 months. VE of the J&J vaccine peaked at 85.8% (95% CI, 74.9 to 91.9) at 2 months and remained higher than 80% through 6 months.

All three vaccines were better at preventing hospitalization and death over time than at preventing infection, although the Pfizer and Moderna vaccines offered more protection than J&J.

The researchers said the results suggest that waning immunity is leading to breakthrough COVID-19 infections, but vaccines maintained effectiveness against hospitalization and severe disease 9 months after the first injection.

"Unlike previous studies, we estimated the vaccine effectiveness in reducing the current risks of COVID-19, hospitalization and death as a function of time elapsed since the first dose," lead author Dan-Yu Lin, PhD, said in an NCCH press release. "This information is critically important in determining the need for and the optimal timing of booster vaccination."

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