Study: Previous COVID-19 infection offers protection against BA.5
Infections with previous COVID-19 variants offer more protection against the Omicron BA.5 subvariant in vaccinated people compared with vaccinated people who had no previous infections, according to a New England Journal of Medicine study yesterday.
The study was based on research conducted at the University of Lisbon in Portugal and is among the first studies to analyze protection against BA.5 among vaccinated and naturally infected people. The authors used the Portuguese national registry of COVID-19 cases to determine which variant likely caused infection based on date and variant predominance. Cases in patients age 12 and older were used.
The researchers found that while natural infections from 2020 and 2021 (when the wild-type strain and the Delta variant were predominant) offered some protection again BA.5, people infected with the BA.1 and BA.2 variants, at the beginning of 2022, who were also vaccinated had four times the protection as those who were only vaccinated.
"This study demonstrates, in the period of time analysed, that previous infection in vaccinated people (the so-called hybrid immunity) continues to confer for the variants that are known for their ability to evade the immune response, such as the subvariant currently dominant," said Valter Fonseca, MD, PhD, co-author of the study, in a press release from the Instituto de Medicina Molecular at the University of Lisbon.
The authors said their findings challenge the perception that protection afforded by previous BA.1 or BA.2 infection is very low.
"Our data indicate that this perception is probably a consequence of the larger pool of persons with BA.1 or BA.2 infection than with infection by other subvariants, and it is not supported by the data," they said.
Aug 31 N Engl J Med study
Aug 31 University of Lisbon press release
37% of a group of Maryland preschoolers with COVID-19 had no symptoms
An 8-month COVID-19 screening study of 175 Maryland households with at least one child aged 0 to 4 years finds that 37% of preschoolers had no symptoms, suggesting that screening only symptomatic children may not be enough to prevent outbreaks in this age-group.
A team led by Johns Hopkins University researchers analyzed weekly symptom questionnaires, self-collected nasal swabs, and sera from 690 participants in 175 Maryland households with one or more children younger than 5 years from Nov 24, 2020, to Oct 15, 2021. The study preceded the emergence of the more transmissible Omicron variant.
Of the 690 participants, 51.4% were female, 37.1% were aged 0 to 4 years, 14.5% were 5 to 17, 48.4% were 18 to 74, 87.4% were White, 6.2% were multiracial, 4.8% were Hispanic, 3.5% were Black, 2.2% were Asian, and 0.7% were of other races.
A total of 7.8% of all participants tested positive for COVID-19, including 22 of 256 children 0 to 4 years old (8.6%), 11 of 100 children aged 5 to 17 years (11.0%), and 21 of 334 adults (6.3%). Infection rates were 2.25 per 1,000 person-weeks among children younger than 5, 3.48 in the 5- to 17-year age-group, and 1.08 among adults.
Children were asymptomatic more often than adults (11 of 30 [36.7%] vs 3 of 21 [14.3%]), with preschoolers having no symptoms at the same rate as older children (7 of 19 [36.8%]). Symptom status didn't correlate with viral load or age, but the number of symptoms was associated with viral load in adults. The highest viral load was greater among participants infected with a Delta variant than among those infected with Alpha or non-variants of concern (VOCs).
Whole-household infection was rare. No fully vaccinated participants were infected with Alpha or non-VOCs, but six vaccinated and eight unvaccinated participants had Delta infections.
"Although the implications of these findings for household transmission remain to be evaluated, they suggest that SARS-CoV-2 infection may be underrecognized and that symptoms may not reflect infectiousness in young children," the researchers concluded.
Aug 31 JAMA Netw Open study