timothy henrich has studied the long term impacts of covid-19. >> the study from the cdc really proves vaccines are going to be necessary to achieve full protection for people who have been previously infected. >> reporter: in the cdc study those who were infected with covid-19 in 2020 experienced a reinfection between may and june of 2021. that's about the same time the delta variant intensified across the u.s. >> hopefully this will push a number of people who have been holding out thinking they don't need a vaccine to go ahead and get vaccinated. >> reporter: the delta variant accounts for more than 83% of virus across the u.s. the president of the gladstone institute agrees with the cdc data but says reinfections could be more than twice as likely to occur. >> we're projecting that the numbers are actually higher than what the cdc is reporting here. >> i think that's very likely because we know that the delta variant is so much more infectious. >> reporter: the latest data shows the mrna vaccines continue to be more than 90% effective in preventing hospitalizations. in san francisc

. >> reporter: ucsf henrich has studied the long term impacts of covid-19. >> the study from the cdc really proves vaccines are going to be necessary to achieve full protection for people who have been previously infected. >> reporter: in the cdc study those who were infected with covid-19 in 2020 experienced a reinfection between may and june of 2021. that's about the same time the delta variant intensified across the u.s. >> hopefully this will push a number of people who have been holding out thinking they don't need a vaccine to go ahead and get vaccinated. >> reporter: the delta variant accounts for more than 83% of virus across the u.s. the president of the gladstone institute agrees with the cdc data but says reinfections could be more than twice as likely to occur. >> we're projecting that the numbers are actually higher than what the cdc is reporting here. >> i think that's very likely because we know that the delta variant is so much more infectious. >> reporter: the latest data shows the mrna vaccines continue to be more than 90% effective in preventing hospitalizations. i