A significant new analysis by Japanese scientists suggests that Covid-19 mRNA vaccines may have been less effective than initially believed, with immune protection dipping much faster than anticipated. This contrasts with earlier claims by the World Health Organization (WHO) and a 2022 study by Imperial College London academics, which estimated that the vaccine rollout prevented between 14.4 million and nearly 20 million deaths worldwide in its first year.

The research, published in Science Translational Medicine by a team from Nagoya University, analyzed antibody data from 2,526 adults in Fukushima between April 2021 and November 2022. All participants had received two doses and a booster of either the Pfizer (BNT162b2) or Moderna (mRNA-1273) vaccine. The study aimed to understand the long-term immune response following booster vaccination.

Over an 18-month follow-up period, four distinct patterns of immune response after the booster were identified: 'durable responders' who maintained high antibody levels; 'rapid decliners' whose levels dropped quickly despite a strong start (approximately 19% of participants); 'vulnerable responders' who produced few antibodies that also fell rapidly (about 28%); and 'intermediate responders'. Crucially, nearly half of the participants (the rapid decliners and vulnerable responders) experienced a substantial loss of antibodies within just nine months of their booster shot.

The study also revealed a modest but notable difference in Covid-19 infection rates. While 5.2% of 'durable responders' were infected, the rate rose to approximately 6% among the rapid and vulnerable groups, representing a relative increase of about 14%. Within three months of a booster, one in five individuals in these categories had contracted Covid, rising to half by six months, compared to only around one in five in the durable group. The researchers concluded that these two groups did not