Why might covid-19 booster vaccinations be needed?

VACCINE-MAKERS HAVE developed covid-19 jabs at unprecedented speed. Now they are turning their attention to booster vaccines. In February Pfizer/BioNTech, the makers of one jab, said they had started a clinical trial looking at giving another shot to people who had already received two doses six to 12 months earlier. This month preliminary data released by Moderna, an American drugmaker, showed that a further dose of one of two jabs, tailored to new variants of the virus and given six to eight months after the first round of vaccinations, triggered a strong immune response against variants first identified in South Africa and Brazil. And this week the Financial Times reported that the vaccine developed by Oxford University and AstraZeneca is effective when used as a booster shot, according to the results of an upcoming study. But some experts argue that there are not yet enough data to determine whether booster shots are even needed. Why might the world require another shot in the arm, and how would booster shots work?

Booster shots are supposed to solve two problems: that immunity tends to wane after vaccination or infection; and that variants might be better at evading the immune system’s defences. Covid-19 vaccines carry out a mock attack on the body for the immune system to practise on. Once the infectious pathogen has been fought off, specialised “memory” B and T cells will stand ready to combat any reinfection. A booster shot is designed to remind the immune system how it responded to a previous infection or teach it to respond to an evolved threat, increasing the level of protection. It could use the vaccine a person received the first time or a slightly modified version.