However, recommending a booster top-up is premature at this stage, says Professor Linda-Gail Bekker. Data from the US, soon to be published, reveal that the vaccine is protective against this highly transmissible variant. The spread of the highly infectious Delta coronavirus variant has thrown many countries a vaccination curveball. It has also been identified in more than 85 countries and has started to dominate third wave Covid-19 infections in South Africa. While data suggest that Pfizer and Moderna's two-dose mRNA vaccines are effective at fighting this variant, the science has been less clear on the one-shot vaccine by Johnson & Johnson. This has led some health experts to believe that following up the single jab with a second dose of mRNA vaccine (by Pfizer or Moderna) may be necessary in the context of this troublesome variant.