Cited by 1,435SARS-CoV-2 and COVID-19 ResearchAnimal Virus Infections StudiesSARS-CoV-2 detection and testing

The DOI matches its Crossref record; 26 of the 26 references it cites were found in a registry or an index; 11 of the 13 sources its claims cite were checked for support.

Development of an inactivated vaccine candidate for SARS-CoV-2

Open access

Published version of a preprint

Abstract

Vaccine candidate tested in monkeys: Global spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an urgent race to develop a vaccine. Gao et al. report preclinical results of an early vaccine candidate called PiCoVacc, which protected rhesus macaque monkeys against SARS-CoV-2 infection when analyzed in short-term studies. The researchers obtained multiple SARS-CoV-2 strains from 11 hospitalized patients across the world and then chemically inactivated the harmful properties of the virus. Animals were immunized with one of two vaccine doses and then inoculated with SARS-CoV-2. Those that received the lowest dose showed signs of controlling the infection, and those receiving the highest dose appeared more protected and did not have detectable viral loads in the pharynx or lungs at 7 days after infection. The next steps will be testing for safety and efficacy in humans. Science , this issue p. 77

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

PiCoVacc, a purified inactivated SARS-CoV-2 vaccine candidate, induced SARS-CoV-2-specific neutralizing antibodies in mice, rats, and macaques and protected macaques against SARS-CoV-2 challenge without observable antibody-dependent enhancement. High-dose immunization (6 μg per dose) provided complete protection in macaques, whereas medium-dose (3 μg per dose) provided partial protection.

Key findings

  • In mice, PiCoVacc elicited S- and RBD-specific IgG that peaked at titers of 819,200 and 409,600, respectively, at week 6; N-specific IgG was ~30-fold lower. Neutralizing antibody titers reached ~1,500 for low/medium doses and ~3,000 for high dose at week 7. In rats, maximum neutralizing titers reached 2,048–4,096 at week 7.
  • PiCoVacc-elicited antibodies neutralized 10 representative SARS-CoV-2 strains in mice and rats, suggesting broader neutralizing activity against circulating strains.
  • In rhesus macaques immunized three times with 3 μg or 6 μg per dose, S-specific IgG and neutralizing antibodies rose to ~12,800 and ~50, respectively, by week 3 before challenge. After intratracheal challenge with 10^6 TCID50 of SARS-CoV-2 CN1, all four high-dose macaques had no detectable viral loads in pharynx, crissum, and lung at day 7; medium-dose macaques showed partial protection with viral blips in pharyngeal (3/4), anal (2/4), and pulmonary (1/4) specimens and ~95% viral load reduction versus sham.
  • Control macaques showed excessive viral genomic RNA copies (10^4–10^6/ml) in pharynx, crissum, and lung by day 3–7 post-inoculation and severe interstitial pneumonia. No fever, weight loss, notable hematological/biochemical/cytokine changes, or histopathological pathology were observed in vaccinated macaques, and no ADE was observed.

Methods

  • SARS-CoV-2 strains were isolated from bronchoalveolar lavage fluid of 11 hospitalized patients; strain CN2 was selected for PiCoVacc, plaque-purified and passaged in Vero cells, propagated in a 50-liter Vero cell culture, inactivated with β-propiolactone, and purified by depth filtration and two chromatography steps.
  • Immunogenicity was assessed in BALB/c mice (n=10), Wistar rats (n=10), and rhesus macaques. Macaques received three intramuscular immunizations at day 0, 7, and 14 with medium (3 μg) or high (6 μg) doses (n=4 per group) for immunogenicity/challenge, or low (1.5 μg) or high (6 μg) doses versus sham/placebo (n=10 per group) for safety.
  • Main analyses included ELISAs for S-, RBD-, and N-specific IgG, microneutralization assays against 10 SARS-CoV-2 strains, qRT-PCR for viral loads, histopathology, hematology, lymphocyte subsets, and cytokine measurements.

Limitations

  • The paper states that the possibility of ADE after antibody titers wane could not be ruled out, and that longer post-vaccination observation of challenged animals is warranted. It also states it is still too early to define the best animal model for studying SARS-CoV-2 infection.
  • Evident from the text: this is preclinical animal data only, with no human safety or efficacy results; macaque immunogenicity/challenge groups were small (n=4), and one medium-dose animal had a ~10-fold higher neutralizing titer that skewed group comparisons.
  • Evident from the text: the medium dose provided only partial protection, with detectable viral blips in some specimens at day 7 after infection.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1126/science.abc1932

Cites

26 of 26 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

11 of 13 cited sources checked · 2 supported · 1 flagged · accuracy not yet measured

Show all 31 claims

  • Probably not a substantial claim. 3
  • It may state two separate claims as one. 17
18 of 18
  • The paper relies on this without support.

    There is an urgent need for a SARS-CoV-2 vaccine because no specific antiviral drugs or vaccines are available.

    “No specific antiviral drugs or vaccines against the newly emerged SARS-CoV-2 are currently available. Therefore, urgency in the development of vaccines is of vital importance to curb the pandemic and prevent new viral outbreaks.”
  • The paper relies on this without support.

    Protection against SARS-CoV-2 challenge in rhesus macaques predicts protective efficacy in humans.

    “These data support clinical development of SARS-CoV-2 vaccines for humans.”
    “Collectively these results suggest a path forward for clinical development of SARS-CoV-2 vaccines for use in humans.”
  • The paper relies on this without support.

    Neutralizing antibody titers are a valid correlate of protection against SARS-CoV-2 in humans.

    “These antibodies neutralized 10 representative SARS-CoV-2 strains, suggesting a possible broader neutralizing ability against SARS-CoV-2 strains.”
    “S-specific IgG and NAb were induced at week 2 and rose to ~12,800 and ~50, respectively at week 3 (before virus challenge) in both vaccinated groups”
  • The paper relies on this without support.

    The absence of observable ADE in macaques during the study period predicts absence of ADE in humans.

    “without observable antibody-dependent enhancement of infection.”
    “No antibody-dependent enhancement (ADE) of infection was observed for the vaccinated macaques despite the observation that relatively low NAb titer existed within the medium dose group before infection, offering partial protection.”
  • The paper relies on this without support.

    The intratracheal challenge with 10^6 TCID50 SARS-CoV-2 CN1 in macaques models natural human SARS-CoV-2 infection sufficiently for evaluating vaccine protection.

    “we conducted a challenge study by a direct inoculation of 106 TCID50 of SARS-CoV-2 CN1 into the animal lung through the intratracheal route at day 22 (one week after the third immunization) in vaccinated and control macaques to verify the protective efficacy.”
    “which probably were caused by a direct inoculation of 106 TCID50 of virus into the lung through intratracheal route, that needed longer time (more than one week) to recover completely (Fig. 3F).”
5 of 5

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Safety-figure time points contradict the vaccination schedule

    Minor

    The stated vaccination days are 0, 7, and 14. Day 18 is 11 days after the second vaccination, not 3; day 29 is 15 days after the third, not 7; and day 1 is not the day of the first vaccination.

1 of 1

Citations

Cites

Flagged first, then by citations

Show all 25 references

Cited by

Sorted by citations

Metadata

Authors
Gao, Q., Bao, L., Mao, H., Wang, L., Xu, K., Yang, M., Li, Y., Zhu, L., Wang, N., Lv, Z., Gao, H., Ge, X., Kan, B., Hu, Y., Liu, J., Cai, F., Jiang, D., Yin, Y., Qin, C., Li, J., Gong, X., Lou, X., Shi, W., Wu, D., Zhang, H., Zhu, L., Deng, W., Li, Y., Lu, J., Li, C., Wang, X., Yin, W., Zhang, Y., & Qin, C.
Affiliations
  • Sinovac Biotech (CN)
  • Chinese Academy of Medical Sciences & Peking Union Medical College (CN)
  • Zhejiang Center for Disease Control and Prevention (CN)
  • National Institutes for Food and Drug Control (CN)
  • Chinese Academy of Sciences (CN)
  • Chinese Center For Disease Control and Prevention (CN)
  • Institute of Microbiology and Epidemiology, Academy of Military Medical Sciences, Beijing, China.
Corresponding author
  • Lu, Jinxing
  • Li, Changgui
  • Wang, Xiangxi
  • Yin, Weidong
  • Zhang, Yanjun
  • Qin, Chuan
Venue
Science
Published
2020-07-03
Volume
369
Issue
6499
Pages
77-81
ISSN
  • 0036-8075 (ISSN-L)
  • 1095-9203
OpenAlex
W3022917947
Cited by
1,434
References
25
Citations by year
2026: 16 · 2025: 38 · 2024: 94 · 2023: 154 · 2022: 286 · 2021: 483 · 2020: 360
FWCI
42.28
Type
journal article
Language
en
Open access
Licence
cc-by
Locations
  • Science (publishedVersion, cc-by)
  • bioRxiv (Cold Spring Harbor Laboratory) (acceptedVersion, cc-by-nc-nd)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Greater South Information System
Funders
  • National Key Research and Development Program (2020YFA0707500)
  • Ten Thousand Talent Program and the NSFS Innovative Research Group (81921005)
Topics
  • Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
  • Life Sciences › Agricultural and Biological Sciences › Animal Science and Zoology › Animal Virus Infections Studies
  • Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 detection and testing
Keywords
SARS-CoV-2, COVID-19 vaccines, inactivated vaccine, neutralizing antibodies, antibody-dependent enhancement, vaccine production, vaccine immunogenicity
MeSH terms
Immunogenicity, Vaccine, Betacoronavirus, COVID-19, SARS-CoV-2, COVID-19 Vaccines, Animals, Antibodies, Viral, Chlorocebus aethiops, Dose-Response Relationship, Immunologic, Female, Immunoglobulin G, Macaca mulatta, Male, Mice, Inbred BALB C, Pilot Projects, Pneumonia, Viral, Vero Cells, Viral Vaccines, Vaccines, Inactivated, Rats, Wistar, Coronavirus Infections, Viral Load, Mice, Rats, Antibodies, Neutralizing, Pandemics

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

A language model drew the claims from the paper on 2026-10-28, under version 3 of the claim definition (model deepseek-v4.1-flash, prompt extract-v3).

A second model labelled each claim on 2026-10-28 (model jev-1.13-20260917, definition revision gold-guideline-v0.2).

Cited sources are checked with a language model’s help (gpt-6-sol).

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review