The following is a summary of some recent studies on COVID-19. They include research that warrants further study to corroborate the findings and that has yet to be certified by peer review.
Breakthrough COVID-19 raises risk of health problems, death
COVID-19 is generally less severe in vaccinated patients but that does not mean breakthrough infections will be benign, a large study shows.
Researchers analyzed data collected by the U.S. Veterans Affairs Administration from 16,035 survivors of breakthrough infections, 48,536 unvaccinated COVID-19 survivors and nearly 3.6 million uninfected people.
At six months after infection, after taking their risk factors into account, people with breakthrough infections had lower rates of death and long-term lingering health problems than COVID-19 patients who had not been vaccinated.
But compared to people who never had COVID-19, those who had breakthrough infections had a 53% higher risk of death and a 59% higher risk of having at least one new medical condition, particularly problems affecting the lungs and other organs.
Even when breakthrough infections did not require hospitalization, the increased risks of death and lasting effects were "not trivial," the research team reported on Monday on Research Square ahead of peer review.
"The overall burden of death and disease following breakthrough COVID-19 will likely be substantial," the researchers conclude.
Vaccine passports would allow infections to be missed
"Vaccine passports" that exempt vaccinated people from regular COVID-19 testing would allow many infections to be missed, Israeli data suggest. Researchers analyzed infection rates in citizens returning to Israel through Ben-Gurion airport, for whom PCR tests upon arrival are required regardless of vaccination status.
"Surprisingly," in August 2021, the rate of positive tests among vaccinated travelers was more than double the rate among the unvaccinated, said Retsef Levi of the MIT Sloan School of Management, coauthor of a report posted on the SSRN server ahead of peer review.
Travelers who had received the second dose of the Pfizer/BioNTech vaccine within the past six months or who had received a booster dose were considered vaccinated.
The group considered to be unvaccinated included the never-vaccinated and those whose most recent shot was more than six months prior, given evidence of waning vaccine efficacy by then.
In September, when the Israeli government was recommending booster shots for all adults, the positive-test rate dropped among vaccinated travelers and was about 3.5 times lower with vaccination than without.
By October, the positive-test rate in the vaccinated group, while still lower, had started to climb again, Levi said. The data suggest that limiting frequent COVID-19 testing to unvaccinated people would "pose potential risks by reinforcing the misrepresentation that vaccinated individuals are protected from infections."
Masks, social distancing still worthwhile
Mask wearing and physical distancing are tied to reductions in the spread of COVID-19 and should be continued, according to researchers who reviewed 72 previous studies.
When they analyzed results from eight of the studies in detail, they saw a 53% reduction in the incidence of COVID-19 with mask wearing and a 25% reduction with physical distancing.
There is not yet enough data to confirm the overall benefits of more stringent measures such as lockdowns, school and workplace closures, and border closures, the researchers reported on Thursday in The BMJ.
Very few of the studies analyzed were randomized trials, so they cannot prove the interventions directly reduced infection rates.
Still, the researchers conclude, "It is likely that further control of the COVID-19 pandemic depends not only on high vaccination coverage and its effectiveness but also on ongoing adherence to effective and sustainable public health measures."