Mixed COVID vaccine schedules offer stronger boost after Sinovac regimen

Giving COVID-19 vaccines from either AstraZeneca-Oxford, Pfizer-BioNTech or Johnson & Johnson as a booster after two doses of the COVID-19 inactivated-virus vaccine from Sinovac, leads to significantly higher antibodies, a study has found.

The best response was seen when an RNA vaccine was given as a booster after the standard schedule of Sinovac’s CoronaVac, researchers from Oxford University said on Monday, adding that the responses were seen against the Delta and Omicron coronavirus variants too.

Sinovac booster shot reverses drop in antibody activities against Delta

Professor Sir Andrew Pollard, Director of the Oxford Vaccine Group and lead of the study, said: “This study shows that the inactivated vaccine, Sinovac’s CoronaVac, can be successfully boosted with a range of different vaccines, with the strongest responses when a viral vector or RNA vaccine is used. The global priority remains first and second doses but this study provides important options for policymakers in the many countries where inactivated vaccines, like CoronaVac, have been used.’

Professor Sue Ann Costa Clemens CBE of the Oxford Vaccine Group, and lead of the study in Brazil, said:

‘The new data presented here show the extraordinary response to a third dose of coronavirus vaccines in a heterologous vaccine schedule, supporting the recommendation of the Brazilian Ministry of Health to use RNA and viral vector vaccines for Brazil’s booster programme. These data will also guide other low- and middle-income countries in setting up the most optimal and affordable booster programmes.’

In the publication, the researchers detail the findings from a randomised study of 1,240 volunteers in São Paulo, and Salvador, Brazil, 1,205 of whom were eligible for inclusion in the final analysis.

These volunteers were divided into four groups, receiving a booster dose of either the Oxford-AstraZeneca, Pfizer-BioNTech, Janssen or Sinovac coronavirus vaccines, six months after their prior immunisations with CoronaVac.

Antibody levels were low prior to delivery of the booster doses, with only 20.4% of adults aged 18-60 and 8.9% of adults aged over 60 having detectable levels of neutralising antibodies. These were seen to significantly increase across every booster vaccine regimen, across all groups, 28 days post-vaccination – with the highest responses recorded after the RNA and viral vector vaccines, including responses against Delta and Omicron.

This increase in binding and neutralising antibodies may improve protection against infection in vaccinated, and boosted, individuals, the researchers conclude.