As people get their boosters in, many are wondering how many more will be needed for adequate protection against Covid-19. Maybe not that many. Repeat booster doses every four months could eventually weaken the immune response and tire out people, the European Medicines Agency warned last week. Instead, countries should leave more time between booster programs and tie them to the onset of the cold season in each hemisphere, following the blueprint set out by influenza vaccination strategies, the regulator said.
The advice comes as some countries consider the possibility of offering people second booster shots amid surging omicron infections. Israel pushed ahead and became the first nation to start administering second boosters, or a fourth shot, to those over 60 as part of the government’s strategy to protect the most vulnerable to the virus. As of Jan. 16, about 537,419 Israelis had received a fourth dose.  Healthcare workers prepare third doses of the Pfizer-BioNTech Covid-19 vaccine. Photographer: Nathan Laine/Bloomberg That contrasts with comments from the U.K., where the government’s advisory panel on inoculations said there’s no immediate need to introduce a second booster to the most vulnerable. Some three months after the third shot, protection against hospitalization among those 65 and older remains at about 90%, data from the U.K. Health Security Agency showed. With just two doses, protection against severe disease drops to about 70% after three months and to 50% after six months. The figures will be reviewed as they evolve. Boosters “can be done once, or maybe twice, but it’s not something that we can think should be repeated constantly,” Marco Cavaleri, the EMA head of biological health threats and vaccines strategy, said at a press briefing. “We need to think about how we can transition from the current pandemic setting to a more endemic setting.” In the meantime, Pfizer is developing a hybrid vaccine that combines its original shot with a formulation that shields against the highly transmissible omicron variant. Pfizer will evaluate the new hybrid formulation against an omicron-specific shot, and determine which is best suited to move forward by March, Chief Executive Officer Albert Bourla said at the JPMorgan Healthcare Conference last week. Pfizer will be ready in March to approach U.S. regulators for clearance of the modified vaccine and bring it to market, and it has already begun production, Bourla said. In Europe, regulators said that April is the soonest they could approve a new vaccine targeting a specific variant, as the process takes about three to four months.—Corinne Gretler and Irina Anghel | 
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