Comparison of AstraZeneca and Sinopharm vaccines as boosters in protection against COVID-19 infection

COVID-19 has caused hundreds of millions of infections globally, and vaccination is the most effective strategy to control disease burden. Multiple vaccine platforms are in use, including inactivated (e.g., Sinopharm/BBIBP-CorV) and adenoviral-vectored vaccines (e.g., AstraZeneca/ChAdOx1 nCoV-19, AZD1222). Given concerns about waning immunity and the emergence of variants such as Omicron, booster doses are recommended. This study investigates whether the type of booster (third dose) affects symptom prevalence and severity among breakthrough COVID-19 cases in adults who received two primary doses of Sinopharm, comparing a homologous Sinopharm booster versus a heterologous AstraZeneca booster.

The paper summarizes coronavirus biology (Coronaviridae taxonomy, transmission via ACE2, mutation/variant dynamics including Omicron) and global non-pharmaceutical interventions. It reviews vaccine platforms (inactivated, live-attenuated, recombinant protein, vectored, mRNA, DNA), regulatory approvals, storage and safety profiles, and prior evidence on immunogenicity and efficacy of Sinopharm (BBIBP-CorV) and AstraZeneca (AZD1222). It notes mixed (heterologous) boosting can enhance humoral and cellular responses and potentially mitigate anti-vector immunity. Prior studies cited report AstraZeneca’s efficacy and safety across trials, Sinopharm’s safety with moderate immunogenicity, and observational data showing reduced severity and mortality among vaccinated individuals.

Design: Cross-sectional study assessing prevalence and severity of COVID-19 symptoms in triple-vaccinated individuals who developed breakthrough infection. Setting and period: Besat Hospital (Tehran, Iran), February–April 2022. Participants: 346 patients with respiratory symptoms underwent SARS-CoV-2 testing by real-time PCR. Of these, 94 were PCR-positive for SARS-CoV-2 and had received three vaccine doses; all had two primary doses of Sinopharm. Booster (third) dose was either Sinopharm (SSS) or AstraZeneca (SSA). Sex, occupation, and residence were not considered. Specimen collection and processing: Nasal and nasopharyngeal swabs collected into VTM, stored at 2–8°C, and tested within one day. Molecular testing: RNA extraction with High Pure RNA Isolation Kit (Roche, Mannheim, Germany). One-step real-time RT-PCR using Qiagen Rotor-Gene Q. Thermal cycling: 50°C 15 min (RT activation), 95°C 15 min (RT inactivation), then 45 cycles of 94°C 15 s, 57°C 30 s for E gene detection, and 58°C 45 s. Positive/negative controls and internal control (RNase P) included. Variables and outcomes: Age group (18–30, 30–50), vaccine regimen (SSS vs SSA), and presence of symptoms (shiver, cough, fever, rhinorrhea, sore throat, backache). Time since last dose: at least 1 month but less than 6 months. Statistical analysis: Categorical variables summarized as n (%). Between-group comparisons by chi-square test or Fisher’s exact test as appropriate; two-sided alpha < 0.05. Analysis performed in R v4.1.3.

• Study cohort: 94 triple-vaccinated, PCR-positive patients analyzed (from 346 symptomatic tested). Age groups: 18–30 years: 30 (32%); 30–50 years: 64 (68%). Vaccine regimens: SSS (three Sinopharm doses): 68 (72.3%); SSA (two Sinopharm + AstraZeneca booster): 26 (27.7%). None were hospitalized; all had non-severe illness.
• Overall symptom frequencies (N=94): cough 100% (94/94), sore throat 72% (68/94), rhinorrhea 65% (61/94), backache 43% (40/94), shiver 40% (38/94), fever 32% (30/94).
• Comparative outcomes by booster type (SSA vs SSS): • Shiver: 23% (6/26) SSA vs 47% (32/68) SSS; p=0.034. • Fever: 15% (4/26) SSA vs 38% (26/68) SSS; p=0.034. • Rhinorrhea: 46% (12/26) SSA vs 72% (49/68) SSS; p=0.019. • Sore throat: 38% (10/26) SSA vs 85% (58/68) SSS; p<0.001. • Backache: 15% (4/26) SSA vs 53% (36/68) SSS; p<0.001. • Cough: 100% in both groups. • Age distribution did not differ significantly between vaccine groups (p=0.26).
• Interpretation: Heterologous boosting with AstraZeneca (SSA) was associated with significantly fewer reported symptoms compared with homologous Sinopharm boosting (SSS).

The findings suggest that among individuals primed with two doses of Sinopharm who experienced breakthrough SARS-CoV-2 infection, an AstraZeneca (AZD1222) booster was associated with reduced prevalence of multiple symptoms compared with a third Sinopharm dose. This aligns with evidence that heterologous booster strategies can enhance immune responses, potentially mitigating limitations such as anti-vector immunity and waning protection. While all cases were non-severe and outpatient, symptom reduction indicates potential benefits of heterologous boosting in lessening clinical burden. These results are consistent with broader literature showing sustained protection of boosters against severe outcomes and support the role of booster dose selection in optimizing breakthrough disease profiles during periods dominated by variants such as Omicron.

Among adults who received two Sinopharm primary doses, an AstraZeneca (AZD1222) booster was associated with fewer and milder symptoms in breakthrough COVID-19 cases than a homologous Sinopharm booster. Booster vaccination appears to reduce severity and may lower hospitalization risk, and heterologous vaccine combinations may be advantageous against severe COVID-19. Further studies should evaluate additional vaccine combinations and compare heterologous versus homologous strategies across broader populations and outcomes.

• Cross-sectional, single-center study over a short timeframe (Feb–Apr 2022), limiting generalizability.
• Small sample size of breakthrough cases (N=94), with unequal group sizes (SSA n=26; SSS n=68).
• Sex, occupation, and place of residence were not collected; potential confounding factors (e.g., comorbidities) not reported.
• Outcomes limited to self-reported/common symptoms; no severe cases or hospitalization outcomes observed in this cohort.
• No viral sequencing to confirm circulating variants; no immunologic correlates (e.g., antibody titers) measured.