Pfizer COVID vaccine shows varied effect against variants, study suggests
One dose of the Pfizer/BioNTech COVID-19 vaccine appears to be not very protective against the B117 variant, and two doses may not be as effective against the B1351 variant, according to a non–peer-reviewed, real-world Israeli study posted late last week on the medRxiv preprint server.
Led by researchers at Tel Aviv University, the case-control study compared nearly 400 people who had received one or two doses of the Pfizer vaccine and were infected by SARS-CoV-2 with matched unvaccinated, infected controls.
Vaccinated participants were infected either at least 1 week after their second dose or between at least 2 weeks after the first dose and before 1 week after the second one. Overall, most infections involved B117, which was first identified in the United Kingdom.
"We see evidence for reduced vaccine effectiveness against the British variant, but after two doses—extremely high effectiveness kicks in," senior study author Adi Stern, PhD, said on Twitter.
B1351, first detected in South Africa, made up about only 1% of all coronavirus cases, but in infected patients who had received two doses of the vaccine, the variant caused eight times more cases than in unvaccinated controls (5.4% vs 0.7%)."We see evidence for reduced vaccine effectiveness against the [South African] variant, but it does not spread in Israel," Stern said.
"Furthermore, focusing on the partially immunized, we noted more breakthroughs by the 'British' variant," she said. "We think this might explain why during the early stages of the vaccination rollout in Israel, it took a while till vaccination effects were noted and cases began to drop."
They added that their findings suggest that the vaccine is less effective against both variants in different dosage and timing scenarios, but cautioned that their study had few participants with B1351 infections. They also said that their study wasn't designed to determine overall vaccine effectiveness against variants, because the participants had already been infected with COVID-19.
"These results overall suggest that vaccine breakthrough infection is more frequent with both [variants of concern], yet a combination of mass-vaccination with two doses coupled with non-pharmaceutical interventions control and contain their spread," the authors wrote.
Apr 9 medRxiv study
Apr 10 SternLab Twitter thread
Study finds 31% of children hospitalized for COVID-19 have severe disease
Editor's Note: This scan was revised on Apr 16. It originally said 12% of children with COVID-19 were hospitalized, which is not correct. We apologize for the error.
Among a cohort of 20,714 US children who sought care from a healthcare provider or emergency department for COVID-19, more than 1 in 10 (11.7%) were hospitalized, of whom 31.1% (756) had severe COVID-19, according to a research letter late last week in JAMA Network Open.
Severe COVID-19 was defined as requiring admission to an intensive care unit (ICU), mechanical ventilation, or comparable treatment.
Discharge data from 869 US medical facilities from Mar 1 to Oct 31, 2020 showed that most hospitalized COVID pediatric patients were girls (52.8%) and 12 to 18 years of age (53.8%); 29.2% had at least one chronic condition. Similar to COVID studies in adult populations, Hispanic and Black populations were overrepresented at 39.3% and 24.4%, respectively. However, when the researchers looked at factors for severe COVID-19, race did not have any significant associations, and neither did insurance type.
The likelihood for severe COVID-19 increased if the patient had at least one chronic condition (adjusted odds ratio [aOR], 3.27; 95% confidence interval [CI], 2.44 to 4.37) or male (aOR, 1.52; 95% CI, 1.26 to 1.83). Likelihood also increased if the child was 2 to 5 or 6 to 11 years of age versus a teenager (aORs, 1.53 for both; 95% CIs, 1.11 to 2.13 and 1.04 to 2.23, respectively).
"Although admission to an intensive care unit for younger children may indicate an abundance of caution by clinicians or facility and administrative requirements rather than disease severity, this finding has important clinical and resource planning implications for facilities and clinicians," the researchers write. "Understanding factors associated with severe COVID-19 disease among children could help inform prevention and control strategies."
Apr 9 JAMA Netw Open research letter
Analysis reveals lower COVID-19 viral load, growth in children
Children may transmit COVID-19 infections less than adults do, according to a study late last week in the Canadian Medical Association Journal (CMAJ). The researchers looked at viral samples from 305 children and adults infected with COVID-19 in Manitoba and found that children's samples had lower viral growth in cultures and higher cycle threshold (Ct) values, indicating less viral load.
Samples were collected March to December 2020 and represent 1.5% of positive COVID samples in Manitoba at the time and 7.2% of the province's positive samples in children. Children were more likely to be symptomatic (37.7% vs 6.9%). For symptomatic children, the researchers note, the duration between symptom onset and testing was not associated with viral culture results.
The researchers were able to successfully culture 30.5% of the samples. They grew viruses in lab culture for 18.6% of samples in children 10 or younger and in 23.1% of samples from children 11 and 17 years—compared with a 43.8% rate in adults, or 55% higher.
Ct values were 25.1 in those 10 and younger, 22.2 in those 11 to 17 years, and 18.7 in adults. The researchers also measured 50% tissue culture infectious dose and found that it was 316 in children 11 to 17 years and 5,620 in adults.
"We found that SARS-CoV-2 grew from pediatric samples less often than adult samples, and when the virus was successfully cultured, significantly less viable virus was present," the researchers conclude. "Finally, we cannot be certain that our findings apply to novel SARS-CoV-2 variants that have shown higher levels of infectivity, as such variants were not commonly circulating during the study period."
In a CMAJ press release, principal investigator Jared Bullard, MD, of the University of Manitoba, added, "If younger children are less capable of transmitting infectious virus, daycare, in-person school and cautious extracurricular activities may be safe to continue, with appropriate precautions in place, and with lower risk to child care staff, educators and support staff than initially anticipated."
Apr 9 CMAJ study
Apr 9 CMAJ press release