In this week's roundup, the latest scientific research on the coronavirus and efforts to find treatments and vaccines suggest that the omicron variant of COVID-19 cannot escape the body's second-line defense, booster shots reduce the risk of omicron's transmission in households and breakthrough infections in cancer patients often become severe.
Omicron and body's defense
A key part of the immune system's second-line defense – its T cells – are highly effective at recognizing and attacking the omicron variant, thereby preventing most infections from progressing to critical illness, a new study shows.
Omicron's mutations help it escape from antibodies, the body's first line of defense against infection. Researchers have speculated that other components of the immune response would still target omicron, but there has been no proof until now.
In test tube experiments, researchers in South Africa exposed copies of the virus to T cells from volunteers who had received vaccines from Johnson & Johnson or Pfizer/BioNTech or who had not been vaccinated but had developed their own T cells after infection with an earlier version of the coronavirus.
"Despite omicron's extensive mutations and reduced susceptibility to neutralizing antibodies, the majority of T cell response, induced by vaccination or natural infection, cross-recognizes the variant," the researchers reported on Tuesday on medRxiv ahead of peer review.
"Well-preserved T cell immunity to omicron is likely to contribute to protection from severe COVID-19," which supports what South African doctors had initially suspected when most patients with omicron infections did not become seriously ill, they said.
The "T" stands for thymus, the organ in which the cells' final stage of development occurs.
Boosters reduce in-house transmission
The odds that vaccinated people will catch the virus if a household member becomes infected are nearly three to four times higher with omicron than with delta, but booster doses reduce that risk, new findings suggest.
Researchers analyzed transmission data collected from nearly 12,000 infected households in Denmark, including 2,225 households with an omicron infection. Overall, there were 6,397 secondary infections in the week after the first infection in the house.
After accounting for other risk factors, the rate of person-to-person spread of the virus to fully vaccinated people was roughly 2.6 times higher in omicron households than in delta households, the researchers reported on Monday on medRxiv ahead of peer review.
Booster-vaccinated people were nearly 3.7 times more likely to get infected in the omicron households than in the delta households, they found.
Looking only at omicron households, however, booster-vaccinated people were 56% less likely to become infected compared to vaccinated people who had not received a booster. And overall, when booster-vaccinated people were the ones who first brought home the virus, they were less likely than unvaccinated and vaccinated-but-not-boosted people to pass it to others.
Breakthrough cases in cancer patients
Vaccinated people with cancer should not underestimate their risks from breakthrough cases of COVID-19, researchers warn.
Among 54 cancer patients who became infected despite receiving a two-dose vaccine from Moderna or Pfizer/BioNTech or a single-dose vaccine from Johnson & Johnson – before booster doses were recommended – 65% needed to be hospitalized, 19% ended up in intensive care units and 13% died, according to data from the international COVID-19 and Cancer Consortium.
The study did not analyze the vaccines' efficacy at preventing infections in the first place. But among those who did become infected, COVID-19 was no less severe than it was in a comparison group of 1,656 unvaccinated cancer patients with COVID-19, researchers reported on Friday in Annals of Oncology. The risks were greatest for patients with blood cancers.
"Many studies ... have suggested that patients with cancer don't create a strong immune response, and this is the first large study that likely shows the consequences of this," said Dr. Jeremy Warner of Vanderbilt University in Nashville, Tennessee.
"Additional doses and boosters are critical, as are continued masking, social distancing, and encouragement of all close contacts of patients with cancer to get vaccinated."