A South African-led study published in the New England Journal of Medicine has shown that two doses of the Pfizer or the Johnson and Johnson (J&J) vaccine are equally effective against severe COVID caused by the omicron variant.
The omicron variant has been shown to escape antibody neutralisation by both the Pfizer/BioNTech mRNA and the Johnson & Johnson adenovirus viral vector vaccine, the only two COVID vaccines available in South Africa. As of May 1, 44.8% of adults in South Africa had been fully vaccinated. Assessing vaccine effectiveness is critical for national vaccine programs.
Starting in October 2021, health care workers who were participating in phase 3b of the Sisonke study of the early vaccine access program were eligible to receive a second dose of the J&J vaccine. Discovery Health data was accessed for Pfizer vaccine effectiveness. Severe COVID was defined as hospitalisation or admission to an intensive care unit (ICU) or to high care.
Vaccine effectiveness was compared between the two vaccine groups according to the number of days since the second vaccine dose had been administered. However longer follow-ups were not available for the J&J group as booster had been initiated later for them.
PCR results were analysed from participants who had received two doses of the Pfizer vaccine given at least 42 days apart or two doses of the J&J vaccine given 4 to 6 months apart. Among these participants, the test positivity rate was 34%; of those with a positive PCR test, 1.6% had been admitted to a hospital and 0.5% to an ICU or to high care.
Effectiveness against hospitalisation in the J&J group, was found to be 55% within 13 days after the second dose, 74% at 14 to 27 days, and 72% at 1 to 2 months. For the Pfizer group, the vaccine’s effectiveness was 81% within 13 days after the second dose, 88% at 14 to 27 days, 70% at 1 to 2 months, 71% at 3 to 4 months, and 67% at > 5 months. Among J&J vaccine recipients, the vaccine effectiveness against ICU admission or high care was 69% at 14 to 27 days and 82% at 1 to 2 months after the second dose; among the Pfizer recipients, effectiveness against ICU admission or high care was 70% at 1 to 2 months, 73% at 3 to 4 months, and 71% at > 5 months.
Gray et al concluded, “After two doses, both vaccines were equally effective against severe disease caused by the omicron variant. These estimates of vaccine effectiveness were calculated in a South African population with a high background prevalence of SARS-CoV-2 exposure during the Covid-19 pandemic. These data provide reassurance about the continued value of the national Covid-19 vaccine program during a surge in the omicron variant.”
