Levels of protective antibodies to the part of the coronavirus that SARS-CoV-2 uses to infect human cells varied widely across each of the four vaccine groups. “Relatively low” antibody concentrations were stimulated by the Sinopharm and Sputnik V vaccines, intermediate levels for the AstraZeneca Plc vaccine, and the highest values for the Pfizer-BioNTech vaccine, a study in the journal Cell Host and Microbe showed. 

The reasons for the differences in immune responses between vaccine types are the subject of intense research. They are likely to include factors such as the amount of active ingredient in each dose and the interval between getting the first and second shots, said the authors from Stanford University, the Onom Foundation, and the National Center for Zoonotic Diseases in Ulaanbaatar in the paper published Thursday. 

Variations in how the vaccines were given could have played a role in the results. The study comparisons were flawed, with more time elapsed between administration of the Sputnik V shot and the antibody measurements than with the other immunizations, according to the state-run Russian Direct Investment Fund, which backed Sputnik V’s development and is in charge of its international roll-out. 

Those getting Sputnik V were also 10 years older than the participants who were given the other shots, the investment fund said.

The study was conducted in July among 196 fully-immunized people in Mongolia, where all four shots were used, a rarity. The results suggested that Sinopharm recipients, who accounted for 89.2% of vaccinated adults in Mongolia at the time, as well as the smaller number of people given Sputnik V or AstraZeneca vaccines, could be susceptible to breakthrough infections, the authors said. 

Booster Shots

“Additional public health interventions, such as booster vaccine doses, potentially with the more potent vaccine types, may be needed to further control the COVID-19 pandemic in Mongolia and worldwide,” they said. 

The study didn’t provide details on the vaccination regimens used, including the interval between doses, which may have underestimated the antibody response to the AstraZeneca vaccine, or study the cellular immune response, said Sam Fazeli, a Bloomberg Intelligence analyst.

Mongolia experienced a summer wave of coronavirus infections due mostly to the alpha variant, the researchers said. High antibody levels were seen in all vaccine groups following a breakthrough infection.

“Faced with the public health crisis of increasing SARS-CoV-2 infections and limited supply or distribution of the most effective vaccines, widespread vaccination with a lower efficacy vaccine may still represent a route to decreasing infections, hospitalizations, and mortality,” the authors said.