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Pfizer recall linked to fewer COVID cases among health workers

Israeli healthcare workers who received a third dose of Pfizer / BioNTech COVID-19 mRNA vaccine had significantly lower infection rates over the next 39 days, a single center says to study yesterday in JAMA.

On July 30, 2021, Israel’s health ministry began offering COVID-19 booster vaccines to people 60 years of age and older, later expanding availability to younger residents. In the United States, boosters are now available for people 12 years of age and older and for 5 to 11 year olds with weakened immune systems.

A team led by researchers at Tel Aviv University assessed rates of SARS-CoV-2 infection among 1,650 healthcare workers with normal immune systems who received a booster dose of Pfizer vaccine after receiving received a second dose a median of 210 days prior and compared to 278 not given a booster. Participants were considered boosted if they had received a third injection at least 7 days before.

Registration took place August 8-19, 2021, after the emergence of the Delta variant (B1617.2), and follow-up ended on September 20. The median age of the participants was 44 years and 71.6% were female. Participants were tested for COVID-19 using the polymerase chain reaction (PCR) every 2 weeks, and their levels of anti-spike immunoglobulin G (IgG) protein antibodies were assessed at baseline and 1 month after receipt of the reminder.

Much lower symptomatic and asymptomatic infection rates

During a median follow-up of 39 days, 44 of 1,928 participants were diagnosed with COVID-19, for an incidence of 0.2 per 100,000 person-days. Five booster recipients were followed for a median of 26 days and 39 unboosted participants were infected, for incidence rates of 12.8 versus 116 per 100,000 person-days, respectively.

A Cox regression analysis over time showed an adjusted risk ratio (aHR) of 0.07 between those who received and those who did not receive a booster. Twenty-eight (71.7%) of 39 unboosted participants and 3 of 5 (60%) boosted participants had symptoms, for incidence rates of 32.7 and 5.1 respectively. The aHRs for symptomatic versus asymptomatic infections were 0.07 and 0.08, respectively.

Among the COVID-19 booster recipients, 953 out of 1,021 (93.3%) reached the peak value measured by the antibody assay, while no significant difference was identified between baseline and follow-up among non-recall beneficiaries.

Post hoc analysis showed a link between lower IgG levels and a higher risk of infection, and multivariate Cox regression revealed that low baseline IgG levels and earlier reception of the initial vaccination schedule were also significantly associated with SARS-CoV-2 infection.

The researchers said the results are consistent with those from previous Israeli booster studies conducted among several age groups and in people over 60. [those with healthy immune systems], a population not included in recent studies on the effect of booster vaccination, “they wrote.” Continuous monitoring is needed to assess the sustainability of the results. “

Fourth doses may not be necessary

In one remark in the same journal, Anna Wald, MD, MPH, of the University of Washington in Seattle, said it is important to determine whether this vaccination is a booster or a third dose. “The interval between vaccine doses is important in terms of achieving lasting immunity, with a longer interval being more likely to establish a lasting response,” she wrote.

Wald said booster doses of COVID-19 could help reduce the risk of transmitting variants of concern. “This is particularly critical during the current Omicron [B.1.1.529] “However, higher levels of neutralizing antibodies after the booster vaccination provide additional protection against the Omicron variant. “

A third dose of COVID-19 mRNA vaccines may elicit a sufficiently robust and long-acting immune response to avoid the need for future boosters, and the formulation of new vaccines that protect against coronavirus proteins less prone to the mutation could lead immunity to a wider population, she added.

“The course and epidemiology of SARS-CoV-2 has not been predictable, and be prepared to respond, such as with effective vaccines and vaccine booster doses as needed as well as with mitigation strategies non-vaccine, remains of crucial importance in helping to reduce SARS – the transmission of CoV-2 and the morbidity and mortality from COVID-19, ”concluded Wald.

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