In this week's roundup, the latest scientific research on the coronavirus and efforts to find treatments and vaccines suggest that although COVID-19 is generally less severe in vaccinated patients, they can still suffer severe symptoms, antibodies in people who had COVID-19 may not protect them against variants, masks and social distancing is still considered worthwhile and 100 million people have had long-haul COVID-19 around the world.

Risk of death in breakthrough cases

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 United States 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 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.

Antibody protection may not last

Nearly everyone who had a mild case of COVID-19 still has antibodies to the coronavirus a year later, but that might not protect them from new variants, a small study suggests.

Among 43 Australians who dealt with mild COVID-19 early in the pandemic, 90% still had antibodies 12 months later. But only 51.2% had antibodies that showed "neutralizing activity" against the original version of the virus and only 44.2% had antibodies that could neutralize the early alpha variant, the research team at the University of Adelaide reported Thursday on medRxiv ahead of peer review.

Neutralizing antibodies against the now dominant and highly transmissible delta variant were seen in only 16.2%, with 11.6% against gamma, and against beta in only 4.6%.

Those who had mild COVID-19 "are vulnerable to infection with circulating and newly emerging SARS-CoV-2 variants 12 months after recovery," the researchers said.

The findings "reinforce the potential benefit" of tailoring vaccine boosters to currently circulating variants, similar to how annual flu vaccines are tailored to current influenza strains, they said.

100 million had long COVID

More than 40% of COVID-19 survivors worldwide have had lingering after-effects of the illness, researchers from the University of Michigan estimate, based on their review of 40 earlier studies from 17 countries that looked at patients' experiences with so-called long-haul COVID-19, defined as new or persistent symptoms at four or more weeks after infection.

The prevalence rises to 57% among survivors who required hospitalization, the researchers reported Tuesday on medRxiv ahead of peer review. The rate was 49% among female survivors and 37% among males, they said.

The estimated long COVID rate was 49% in Asia, 44% in Europe and 30% in North America. Among the most common problems, fatigue was estimated to affect 23%, while shortness of breath, joint pain and memory problems each affected 13%.

The study likely did not capture all cases of long COVID, the researchers say.

"Based on a WHO (World Health Organization) estimate of 237 million worldwide COVID-19 infections, this global pooled ... estimate indicates that around 100 million individuals currently experience or have previously experienced long-term health-related consequences of COVID-19," they reported.

These health effects, they warn, "can exert marked stress on the health care system."

Masks 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 wearing masks 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 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."