Age, sex, body mass index and smoking are factors that affect the effectiveness of vaccines against covid-19, as found by research from the University of California published in the journal “Scientific Reports”.

In the June 2021 study, researchers monitored the response to vaccines from Pfizer, Moderna, Johnson & Johnson in blood samples 498 healthy volunteers, aged 18-88 years. They measured the levels of neutralizing antibodies produced by the vaccination preventing infection with Covid-19.

One month after vaccination those who got the Pfizer vaccine had an antibody response 21 times higher than those who got Johnson & Johnson, while those who got Moderna had a response 51 times higher than those who got Johnson & Johnson. To ensure accuracy, volunteers were screened for prior Covid-19 infection before receiving the vaccine, and any prior infection was taken into account in the calculation of antibody levels.

The surprise was that at six months after vaccination those vaccinated with Johnson & Johnson surpassed the antibody levels of those who received Pfizer and reached similar antibody levels to those vaccinated with Moderna, as antibody levels for the other Pfizer and Moderna vaccines declined.

Furthermore, the researchers found that and other factors affected the effectiveness of vaccines. Among older adults, antibodies were 17% lower for those given Pfizer and 11% lower for those given Johnson & Johnson, but remained the same for those vaccinated with Moderna. In those with a higher body mass index, antibodies were 11% lower in those vaccinated with Johnson & Johnson but not in those vaccinated with Pfizer or Moderna.

To men antibodies were 30% lower than in women regardless of vaccine brand and to smokers were 240% lower than non-smokers, again independent of vaccine brand.

The researchers point out that the findings of the study may also apply to new vaccines involving the Omicron variants, and the next phase of research will focus on the effectiveness of these new vaccines.