Rising number of breakthrough Delta infections among fully vaccinated

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Chicago: A quarter of Los Angeles residents who caught COVID from May through July this year as the Delta variant surged were fully vaccinated.

The data, published in the US Centres for Disease Control and Prevention’s weekly report on death and disease, shows an increase in “breakthrough” infections among those who had both doses of a coronavirus vaccine.

The centre is relying on data from cohorts, such as the Los Angeles County study, to determine whether Americans need a third dose of COVID-19 vaccines to increase protection. Government scientists last week laid out a strategy for booster doses beginning on September 20, pending reviews from the US Food and Drug Administration and the CDC.

While a quarter of the COVID infections in the Los Angeles study were in the fully vaccinated, fewer than one in 20 was hospitalised. Credit:AP

The new data released on Tuesday involved more than 43,000 reported infections among Los Angeles County residents aged 16 and older. Of them, 10,895, or 25.3 per cent occurred in fully vaccinated persons, and 1,431, or 3.3 per cent, were in partially vaccinated persons. The majority of infections, however, were among the unvaccinated: 30,801 cases, or 71.4 per cent of the cohort.

The vaccines did, however, protect individuals from more severe symptoms. According to the study, only 3.2 percent of fully vaccinated individuals who tested positive for coronavirus were hospitalised, just 0.05 per cent were admitted to an intensive care unit and 0.25 per cent were placed on a ventilator.

Among the unvaccinated who caught COVID, 7.5 per cent were hospitalised, 1.5 per cent were admitted to an intensive care unit and 0.5 per cent required breathing support with a mechanical ventilator.

In addition to the LA County data, the CDC on Tuesday released an update on a study of healthcare workers that showed a significant drop in vaccine effectiveness among vaccinated frontline workers in eight states who became infected with the coronavirus.

The effectiveness of COVID-19 vaccines among healthcare workers declined to 66 per cent after the Delta variant became dominant, compared with 91 per cent before it arose, according to the report.

The vaccines are still protective, the centre said, and the finding must be interpreted with caution, as vaccine effectiveness might wane over time and the estimates of efficacy were imprecise.

“Although these interim findings suggest a moderate reduction in the effectiveness of Covid-19 vaccines in preventing infection, the sustained two-thirds reduction in infection risk underscores the continued importance and benefits of Covid-19 vaccination,” researchers wrote in the agency’s Morbidity and Mortality Weekly Report.

The findings echo earlier evidence from Israel and the UK suggesting COVID-19 vaccines lost some potency in preventing infections over time as the Delta variant spread.

The observational study tracked more than 4,000 health-care workers, first responders, and other front-line personnel in eight locations across six states from December 2020 to August 2021. They were tested weekly for COVID-19 infection, and about 83 per cent were vaccinated.

About two-thirds of those vaccinated had received the Pfizer shot, 2 per cent received Johnson & Johnson’s, and the rest received the Moderna vaccine.

Dr Anthony Fauci, the nation’s top infectious disease expert, said the United States could get COVID-19 under control by early next year if vaccinations ramp up.

The day after Pfizer won full approval for its shot from the Federal Drug Agency, Fauci said in several television interviews and a White House press conference that he expected Moderna to get full authorisation in coming weeks and clearance for younger children to get vaccinated by early autumn when the American school year begins.

Reuters, Bloomberg

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