nly about 0.01% of people became infected with Covid-19 between January and April (2021) despite being fully vaccinated, a US government study confirming the shots’ high efficacy showed on May 26 (2021).
The report published by the US Centers for Disease Control and Prevention (CDC) documented so-called “breakthrough” cases among 101 million people fully vaccinated in the United States.
“Even though FDA-authorised vaccines are highly effective, breakthrough cases are expected, especially before population (or herd) immunity reaches sufficient levels to further decrease transmission, ” the report said.
It examined the period from Jan 1 to April 30 (2021).
A total of 10,262 infections were documented at 14 days or more after the final dose of a vaccine provisionally authorised by the US Food and Drug Administration (FDA) for that time period, i.e. Pfizer/BioNTech, Moderna or Johnson & Johnson.
Of these cases, 6,446 (63%) occurred in females, and the median patient age was 58 years.
Among the total number of breakthrough cases, 2,725 (27%) were asymptomatic, 706 (7%) were hospitalised for reasons related to Covid-19, and 132 (1%) died from reasons related to Covid-19.
The rate of breakthrough infections were thus roughly 0.01%, hospitalisations were 0.0007% and deaths were 0.0001%.
The genomic sequences were available for 5% of all infections and showed that 64% of cases came from viral variants of concern.
The most significant was the B.1.1.7 variant that was first identified in the United Kingdom.
The study occurred during a period when the SARS-CoV-2 virus was surging through the US, with approximately 355,000 cases reported in the last week of April (2021) alone.
“The number of Covid-19 cases, hospitalisations and deaths that will be prevented among vaccinated persons will far exceed the number of vaccine breakthrough cases, ” the authors wrote.
The US CDC noted that the actual number of vaccine breakthrough cases is likely to be substantially higher because most will result in asymptomatic or mild infections that won’t be tested.
The data on viral variants is also limited by the lack of widespread surveillance systems.
On May 1 (2021), the US CDC switched from monitoring all data on breakthrough infections to only looking for severe cases and deaths, which are of greater clinical importance.
But some scientists said they would be missing out on valuable data and criticised the decision.
About 164 million people – half of the total US population – have now had at least one dose of a Covid-19 vaccine, while 39% have been fully vaccinated. – AFP Relaxnews