Research explores the exponential growth, high prevalence of SARS-CoV-2 and the effectiveness of Delta-related vaccines

Despite the high vaccination rate, the epidemic of coronavirus SARS-CoV-2 infection continues to drive morbidity and hospitalization rates.
In many populations, the proportion of cases caused by the Delta variant of this virus is increasing
.

With the global expansion of vaccination plans and the relaxation of social distancing, the future trend of SARS-CoV-2 is uncertain

Since May 2020, the REACT-1 (Real-time Assessment of Community Transmission-1) study has been tracking the spread of the COVID-19 pandemic in England
.

Based on a random sample of people aged 5 and over in England, the study involved obtaining homemade throat swabs and nasal swabs from approximately 100,000 or more people within 2 to 3 weeks of each month for reverse transcription polymerase chain reaction ( RT-PCR) detection

These researchers observed that with the development of the third round of the epidemic in England, the reproduction number R was estimated to be 1.
44 in the 12th round (95% confidence interval 1.
20, 1.
73), and 1.
19 (1.
06, 1.
32) in the 13th round.
The average doubling time corresponding to the 12th and 13th rounds were 11 days (7, 23 days) and 25 days (15, >50 days), respectively
.

This resulted in an increase in the average weighted prevalence rate from 0.

During 2021, the replacement of SARS-CoV-2 variants led to an increase in infections and raised concerns about the effectiveness of vaccines against infections
.

Picture from Science, 2021, doi:10.

Among participants aged 18 to 64, based on self-reported vaccination status, these authors estimated the effectiveness (adjusted for age, gender, region, race, and multiple poverty index) against infection in round 13 to 49% ( The 95% confidence interval is 22%, 67%).
If only strong positives are considered [cycle threshold (Ct) is lower than 27], it rises to 58% (33%, 73%)
.

For the same age group, they estimated the effectiveness of the infection adjusted to 59% (23%, 78%), that is, one or more common COVID-19 symptoms (fever, loss of smell or taste were reported one month before the test) Or change, new persistent cough)

In summary, from the end of May to the beginning of July 2021, a very successful vaccination campaign was carried out in the United Kingdom.
The vaccination rate was high, but among the unvaccinated young people, the Delta variant infection rate was higher.
, Which promotes an exponential increase in infections
.

Although the growth rate in the northern hemisphere has slowed in the summer of 2021 (or the prevalence is flat or declining), in the presence of the Delta variant, the increased mix may explain the re-growth that occurred in the fall of 2021, even at higher vaccination levels.

Note: The original text has been deleted

Reference materials:

Paul Elliott et al.