Effectiveness of an inactivated Covid-19 vaccine with homologous and heterologous boosters against Omicron in Brazil

Abstract

The effectiveness of inactivated vaccines (VE) against symptomatic and severe COVID-19 caused by omicron is unknown. We conducted a nationwide, test-negative, case-control study to estimate VE for homologous and heterologous (BNT162b2) booster doses in adults who received two doses of CoronaVac in Brazil in the Omicron context. Analyzing 1,386,544 matched-pairs, VE against symptomatic disease was 8.6% (95% CI, 5.6–11.5) and 56.8% (95% CI, 56.3–57.3) in the period 8–59 days after receiving a homologous and heterologous booster, respectively. During the same interval, VE against severe Covid-19 was 73.6% (95% CI, 63.9–80.7) and 86.0% (95% CI, 84.5–87.4) after receiving a homologous and heterologous booster, respectively. Waning against severe Covid-19 after 120 days was only observed after a homologous booster. Heterologous booster might be preferable to individuals with completed primary series inactivated vaccine.

Waning vaccine response to severe COVID-19 outcomes during omicron predominance in Thailand

“…We found that the protection against severe COVID-19 was highest with boosters received >14 days to 2 months prior to positive test (93%) and persisted between 2-4 months (91%) but started to wane between 5-6 months (77%) and further beyond 6 th month (68%). Our results are consistent with ndings from the US [16], Brazil [17] and Finland [18], where effectiveness of booster vaccines against COVID-19associated severe outcomes started to decline after 4 months.…”

“…Similar results were seen in Brazil, where protection waned after 3-4 months from last booster vaccine, and the decline was more rapid with homologous schedules as compared to heterologous schedules [17]. Previous studies examined waning of booster vaccine effectiveness against severe outcomes in populations with predominantly homologous schedules [15,16,18] and only a handful of studies have examined heterologous schedules [17,19,20].…”

“…A recent US-CDC study found that among recipients of three doses, effectiveness against COVID-19-associated hospitalizations declined from 89% among those vaccinated within the past 2 months to 66% among those vaccinated 4-5 months earlier [16]. Similar results were seen in Brazil, where protection waned after 3-4 months from last booster vaccine, and the decline was more rapid with homologous schedules as compared to heterologous schedules [17]. Previous studies examined waning of booster vaccine effectiveness against severe outcomes in populations with predominantly homologous schedules [15,16,18] and only a handful of studies have examined heterologous schedules [17,19,20].…”

“…[16], and Ranzani et al, [17], where a more rapid decline in vaccine effectiveness was seen among older adults. This evidence strengthens the need for a more targeted approach in protecting the older age groups who remain more vulnerable, either through booster vaccinations or additional preventive measures.…”

Neutralizing and Total/IgG Spike Antibody Responses Following Homologous CoronaVac vs. BNT162b2 Vaccination Up to 90 Days Post-Booster

“…Between 0–13 days and >180 days, the odds in 18–39-year-olds were 1.41 to 1.67, but they were 1.22 to 1.65 in those > 80 years old. In a study of the effectiveness of heterologous vs. homologous booster regimens, a homologous inactivated virus vaccine booster only resulted in a vaccine effectiveness of 15.0% against symptomatic COVID-19 8–59 days post-vaccination compared with 56.8% when given an mRNA vaccine booster, with higher vaccine effectiveness against hospitalization and death ≥ 60 days after the booster in heterologous vaccinees (78.5% vs. 51.4%) [ 20 ]. In combination, these studies seem to indicate that the declining antibody responses in inactivated virus vaccinees are associated with a decline in vaccine efficacy over time.…”