A study looking at the effectiveness of fourth doses of COVID-19 vaccines, run by the U.S. Centers for Disease Control and Prevention, has found that a second booster shot of an mRNA vaccine has significant effectiveness against severe illness with some Omicron variants.
After the first booster shot, vaccine effectiveness against severe illness with Omicron variants BA.1 and BA.2/BA.2.12.1 was found to be just 68 per cent in the first six months, declining to 52 per cent after that point, according to the CDC.
Shaun Grannis, vice-president for data and analytics at the Regenstrief Institute and professor of family medicine at Indiana University School of Medicine, as well as co-author of the study,that these findings may help some people answer the question of whether they should get a second booster shot.
In the U.S., this eligibility refers to people over the age of 50 years old, as well as younger people who are moderately to severely immunocompromised, according to the CDC’s current recommendations. This new study only included those that fell within this group. Vaccine effectiveness was assessed by comparing the odds of hospitalization or emergency department visits between those vaccinated with one, two, three or four doses, as well as those who are completely unvaccinated.