Understanding the Debate Over Covid Booster Shots
The rise of the delta strain, combined with some preliminary data suggesting that Covid vaccine effectiveness may decline relatively quickly, has intensified the focus on booster shots. In Mesa County, Colorado, where delta took off earlier than in other parts of the state, a study by state health officials found that vaccines were 78% effective in a two-week period ending June 5, versus 89% in other counties. And an observational study from Israel, one of the first countries to vaccinate most of its population, suggested that a third dose of the Pfizer-BioNTech shot dramatically boosted protection in people 60 and over, at least in the short term. According to the data published in the New England Journal of Medicine, confirmed infection rates were 11 times lower in the booster group compared to those who had only gotten the standard two doses starting 12 days after the third dose. A separate analysis of data from the final-stage trial of the Pfizer-BioNTech vaccine showed that efficacy eased to about 84% at the end of a six-month period compared with 96% early on.