Seroconversion and adverse events in the first month after the
administration of two doses of the inactivated SARS-CoV-2 vaccine in
Turkey: Is a booster dose required?
Aims: Limited information is available about the efficacy and adverse
events of COVID-19 vaccines introduced into public use with Emergency
Usage Licences without completing phase-3 trials. Data refer to healthy
and mostly younger people, with lacking evidence about the protectivity.
This study aimed determining seroconversion rates and levels specific to
anti-S-RBD IgG and total anti-spike/anti-nucleocapsid IgM and IgG
antibodies against SARS-CoV-2 after the administration of two doses of
the inactivated SARS-CoV-2 vaccine in Turkey, comparing three types of
antibodies. It was also aimed to assess short-term adverse events due to
the vaccine. It is intended to answer the questions about efficacy and
safety, which lack in phase trials, especially at community level. It is
also aimed to collect data, which will form the basis for assessing
whether antibodies are protective at different community settings.
Methods: The study carried out in Turkey, comprised 282 healthcare
workers who received two doses of the inactivated SARS-CoV-2 vaccine
administered in two 3µg doses, 28 days apart. In day-28 after the second
dose, anti-S-RBD IgG and total anti-spike/anti-nucleocapsid IgM and IgG
antibodies against SARS-CoV-2 were detected by in-vitro
chemiluminescence immunoassay. Results: At day 28 after the second dose,
the seroconversion rates were found to be 92.9% for total
anti-spike/anti-nucleocapsid IgG and 15.2% for IgM and 98.2% for
anti-S-RBD IgG antibodies. The immunogenicity was affected by
pre-vaccination natural COVID-19 history and age. The incidence of at
least one adverse event was found as 29.8% after the first dose and
24.1% after the second dose, with the most common events being pain at
the injection site, weakness, fatigue and headache. Conclusion: A high
rate of seroconversion was observed with no serious adverse events.
Prior natural COVID-19 history and age significantly contributed to
strong immunogenicity. A booster dose appears required for older ages
and individuals without immune response.