Adverse events after COVID-19 vaccination self-reported by healthcare workers are reliable

We wish to thank Dr. Finsterer’s comments on our article published in Human Vaccine & Immunotherapeutics.¹ In our article, the overall incidence of any self-reported adverse events (AEs) after the first and second dose of COVID-19 vaccine composed of inactivated SARS-CoV-2 among Chinese healthcare workers (HCWs) was 38.2% (532/1392) and 31.0% (325/1047) respectively, and none of the vaccinated HCWs reported severe AEs and required hospitalization.² Dr. Finsterer concerned that, in contrast to the reported severe AEs after administration of COVID-19 mRNA vaccines (Biontech Pfizer or Moderna vaccine) or adenovirus vector vaccines (Astra Zeneca or Johnson and Johnson Vaccine), no severe AE was observed in Chinese HCWs vaccinated with China-made inactivated COVID-19 vaccines. Thus, Dr. Finsterer proposed that China-made vaccines may have a lower risk of AEs or that severe side effects were not published due to political, economical, or personal reasons.¹

As AEs presented in our article were self-reported through filling in the questionnaires by HCWs,² Dr. Finsterer considered that HCWs who had severe AEs after vaccination were unable to participate in the investigation, leading to missing the severe AEs.¹ Indeed, we could not absolutely exclude such a possibility. However, other doubts, such as filling in the questionnaire by a third person or unwillingness to consent severe AEs,¹ are unlikely. We clearly stated at the beginning of the questionnaire that “The questionnaire is anonymous. Whether or not answering the questionnaire is all determined based on your own willingness, and will not influence any of your interests and will not cause any negative effect to you. If you are willing to participate in this survey, please complete the questionnaire independently and objectively.”² Based on the survey contents,² the identity of participants cannot be identified, and anonymity of the participants is guaranteed. Thus, if the participants did not want to participate in the survey, they could decline, and they had no incentive to have a third party to fill out the questionnaire.

Dr. Finsterer concerned that HCWs working in public institutions may hold back the severe AEs that they had truly experienced because of fear of getting into troubles with the employer.¹ However, such a thing is less likely to occur nowadays in China. In fact, several Chinese scholars reported several severe AEs after vaccination with China-made inactivated COVID-19 vaccines.^3,4 Moreover, we are independent investigators, not employers; the participants enrolled in our study had no reason or motivation to hold back severe AEs if they had really experienced.

The phase 3 clinical trials of inactivated COVID-19 vaccines (Aikewei [Sinopharm] and/or CoronaVac [Sinovac], Beijing, China) were not conducted in China because of the ‘zero’ infection of SARS-CoV-2 after the first wave of the pandemic, but conducted in other countries, among tens of thousands of people in the United Arab Emirates and Bahrain,⁵ Turkey,⁶ Indonesia,⁷ or among more than 4 millions of persons in Chile,⁸ however, severe AEs were rarely reported. The real-world data in other countries, such as Turkey, Iran, and Algeria, show that the incidence of any AEs and severe AEs in people vaccinated with China-made inactivated COVID-19 vaccines is much lower than that in those who were vaccinated with mRNA or adenoviral-backbone COVID-19 vaccines.^9–11 As of 15 June 2022, in addition to the use of over 3.39 billion doses in mainland China, more than 2.2 billion doses of China made inactivated COVID-19 vaccines were rolled out in more than 120 countries or regions. However, severe AEs after vaccination of these inactivated COVID-19 vaccines were very rarely reported. A case-control study conducted in Hong Kong, where inactivated vaccine CoronaVac (Sinovac) and mRNA vaccine BNT162b2 (Pfizer-BioNTech) were both approved, showed an elevated risk for carditis after the use of BNT162b2 but not after the use of CoronaVac, by comparing the incidence of carditis between 3.29 million persons who received either CoronaVac (2 291 444 doses) or BNT162b2 (3 496 629 doses) and those who did not receive COVID-19 vaccine.¹² In addition, an inactivated COVID-19 vaccine prepared in India also showed highly safe in tens of thousands of persons, without severe AEs.¹³

In summary, the self-reported AEs after COVID-19 vaccination in Chinese HCWs in our article²reflected the real situations. Together with the results reported by investigators in China and other countries, COVID-19 vaccines composed of inactivated SARS-CoV-2 have relatively low incidence of severe AEs, compared to mRNA or adenovirus-based COVID-19 vaccines.

Funding Statement

The author(s) reported there is no funding associated with the work featured in this article.

Disclosure statement

No potential conflict of interest was reported by the author(s).