Data suggest third COVID vaccine dose reduces infection, hospitalization
A third dose of the Pfizer/BioNTech mRNA COVID-19 vaccine appears to counteract waning vaccine protection in the short term, according to a preliminary case-control analysis of more than 500,000 coronavirus tests in Israel.
In the retrospective study, published yesterday in JAMA Internal Medicine, a team led by Maccabi Healthcare Services researchers found a 1.8% SARS-CoV-2 infection rate after a booster dose, compared with 6.6% after two vaccine doses. Participants receiving the booster also seemed to be at lower risk for hospitalization.
The study involved 306,710 Israelis 40 years and older who received two or three doses of the vaccine and did not have a previous COVID-19 infection. Data were collected from Mar 1, 2020, to Oct 4, 2021—a period that included the emergence and eventual dominance of the Delta (B1617.2) variant—while analysis focused on the period of Aug 1, 2021, when third doses were rolled out, to Oct 4. Booster recipients were tested for COVID-19 five times over the study period.
Positive tests were most common in those who did not receive a booster and those who received a booster within the past week; they were least common among those who received a booster more than 2 weeks before.
The estimated odds ratio for infection was 0.14 for those receiving two doses relative to those receiving boosters, for an 86% reduction in the odds of infection.
"However, these results should be interpreted with caution because a reduction in the odds of hospitalization was already evident in the first week after receipt of the booster when an effect would not be expected," the study authors noted
The chances of hospitalization among those who received a booster were 92% to 97% lower than among those who received two doses. "The interpretation of these estimates for hospitalization is challenging; however, the apparent immune response of the booster was evident as soon as a few days after its receipt (87% measure of effectiveness at 0-6 days)," the study authors wrote.
More follow-up is needed to determine how long third-dose immunity lasts, the researchers concluded.
Nov 30 JAMA Intern Med study
Children with poorly controlled asthma at higher risk of severe COVID-19
A study yesterday in The Lancet Respiratory Medicine of Scottish children shows that 5- to 17-year-olds with poorly controlled asthma are three to six times more likely to be hospitalized with COVID-19 compared with those without asthma. The authors of the study said children with asthma should consider vaccination against COVID-19 as soon as possible.
The study was based on health records from more than 750,000 children. Among those, 63,463 had asthma, and among that group, there were 4,339 confirmed cases of COVID-19 from Mar 1, 2020, to Jul 27, 2021. Sixty-seven of those children required hospitalization.
Children with poorly controlled asthma—defined as recent hospitalization for asthma, or two or more courses of oral corticosteroids—were more likely to be hospitalized. For children with a recent hospital admission for asthma, the hazard ratio (HR) was 6.4, compared to 1.6 for children with controlled asthma. Children who had reported steroid use at least twice in the past had an HR of 3.53.
Among children without asthma, there were 40,231 confirmed cases of COVID-19, 382 of which involved hospitalization.
"The key takeaway from this study is that keeping children's asthma under control is critical, as this greatly reduces the risk of COVID-19 hospitalisation," said senior author Aziz Sheikh, PhD, from the University of Edinburgh, Scotland, in a Lancet press release. "Vaccinating those with poorly controlled asthma offers an additional important layer of protection from serious COVID-19 outcomes."
In a commentary published on the study in the same journal, two UK experts who were not involved in the study point out that even with poorly controlled asthma, serious complications from COVID-19 were still extremely rare in Scottish children.
"Careful decision making around the delivery of the vaccine to children younger than 12 years is essential. Although children with asthma have been identified as having an increased risk of being admitted to hospital compared with peers without asthma, the overall risk remains very low," they write.
Nov 30 Lancet Resp Med study
Nov 30 Lancet press release
Nov 30 Lancet Resp Med commentary