Currently, in some countries (including Spain) 70% or more of the population has been vaccinated against the coronavirus. However, it is being evaluated whether this percentage implies a definitive protection against COVID-19 or not.
In this sense, a very interesting study has been published in the New England Journal of Medicine. At the University of California, vaccination began in December 2020 and by July this, 83% of health personnel were already vaccinated with both doses. However, coinciding with the release of the mandatory use of the mask and with the appearance of the Delta virus variant, there has been an increase in infections, even among people who were already vaccinated.
Thus, between March 1 to July 31, 227 coronavirus infections were detected among health personnel, of which 130 (57%) were already fully vaccinated. Of those 130 vaccinated and infected people, 109 (84%) had symptoms of the disease and also 80 of the 90 (89%) unvaccinated workers (the remaining 7 infected people had received a single dose of the vaccine). There were no deaths and only one person (not vaccinated) had to be hospitalized. The frequency of coronavirus infection was 3.7 per 1,000 people among the vaccinated and 16.4 per 1,000 among the unvaccinated.
Efficiency against the delta variant of the coronavirus
These data suggest that the efficacy of the vaccine is considerably lower against the delta variant. It can also influence, according to this article, the decrease in protection achieved with the vaccine over time.
In addition, these findings highlight the importance of reusing masks and increasing diagnostic tests trying to avoid the expansion of the delta variant. The authors also suggest that a booster dose of the vaccine could be considered.