“delta is different from previous strains,” the cdc document noted.
crucially, the document also cited studies showing that people who are fully vaccinated can transmit the delta variant of covid-19 almost as easily as those who are not vaccinated. in a reversal of earlier advice, the cdc recommended masking in high transmission areas this week, even for people who are fully vaccinated.
vaccines prevent 90 per cent of severe disease, but may be less effective at preventing infection or transmission of delta, which means it can lead to more breakthrough infections (in people who are vaccinated) and more community spread, according to the cdc.
the cdc also released results of a study looking at a cluster of cases in massachusetts in july. seventy four per cent of those infected were fully vaccinated. the concerning data was pivotal to the cdc’s recommendation about masking this week, director dr. rochelle walensky said.
on friday, chief public health officer of canada dr. theresa tam said models suggested canada was already at the start of a delta-driven fourth wave. the trajectory of that wave will depend on increasing vaccination coverage as well as the “timing, pace and extent of reopening.”