The science of these particular mRNA vaccines didn't say that. The empirical data from UK and Israel, the 2 fastest vaccinated countries actually are opposite to that claim. Your linked article is too old, dated on March when vaccination in U.S. was around 10%. How could they make such claim based on such incomplete data? See the linked UK data. the infected case rose sharp after their vaccination (at same time, the 2nd chart shows the hospitalized is very low despite increased cases, indicating delta variant spreads fast but seems less deadly. This is the reason why I think/hope this variant is candidate of natural vaccine).
Link: https://www.dailymail.co.uk/news/article-9814957/Britains-daily-Covid-cases-time-two-months.html