One in three people who overcome Covid-19 suffers from a neurological or psychiatric diagnosis six months on, according to the largest study so far published on the mental toll that long-Covid takes on survivors.

Authors said the research, printed Wednesday in The Lancet Psychiatry journal, proved that Covid-19 patients were significantly more likely to develop brain conditions than those suffering from other respiratory tract infections.

Studying the health records of more than 230,000 patients who had recovered from Covid-19, they found that 34 percent were diagnosed with a neurological or psychiatric condition within six months. 

The most common conditions were anxiety (17 percent of patients) and mood disorders (14 percent).

For 13 percent of patients the disorders were their first diagnosis of a mental health issue. 

Incidence of neurological disorders such as brain haemorrhage (0.6 percent), stroke (2.1 percent) and dementia (0.7 percent) was lower overall than for psychiatric disorders but the risk for brain disorders was generally higher in patients who had severe Covid-19.

The authors also examined data from more than 100,000 patients diagnosed with influenza and more than 236,000 diagnosed with any respiratory tract infection.

They found there was overall a 44 percent greater risk of neurological and mental health diagnoses after Covid-19 than after flu, and a 16 percent higher risk than with respiratory tract infections.

Paul Harrison, lead author from the University of Oxford, said that while the individual risk of neurological and psychiatric orders from Covid-19 was small, the overall effect across the global population could prove to be "substantial".

"Many of these conditions are chronic," he said.

"As a result, health care systems need to be resourced to deal with the anticipated need, both within primary and secondary care services."

- 'Severe impact' -

Patients hospitalised with severe Covid-19 were at great risk of developing long-term conditions, according to the analysis.

For example, 46 percent of patients who needed intensive care were diagnosed with neurological or psychiatric conditions within six months of recovery.

The data showed 2.7 percent of people needing intensive care suffered a subsequent brain haemorrhage, compared to 0.3 percent of people who weren't hospitalised.

And nearly 7 percent of those needing ICU care suffered a stroke, compared with 1.3 percent of patients who didn't.

Writing in a linked comment article, Jonathan Rogers from University College London, said further research was needed on the long-term neurological and psychiatric outcomes among Covid-19 patients.

"Sadly, many of the disorders identified in this study tend to be chronic or recurrent, so we can anticipate that the impact of Covid-19 could be with us for many years," said Rogers, who was not involved in the study. 

"It is clear from this study that the impact COVID-19 is having on individuals mental health can be severe," said Lea Milligan, CEO of the MQ Mental Health research group.

"This is contributing to the already rising levels of mental illness and requires further, urgent research."

Chile study

A study in Chile, which has one of the furthest-advanced vaccination campaigns in South America -- mainly with China's Coronavac, has found that a first dose alone does not protect against coronavirus infection.

The study by the University of Chile found inoculation to be 56.5 percent effective in protecting recipients two weeks after the second dose, and 27.7 percent effective within the first two weeks.

But for a single dose, efficacy in the 28 days between the first and second dose was only three percent -- on par with the margin of error in such studies, it said.

Researchers looked at the combined effect of Coronavac, which accounts for about 93 percent of doses being administered, and the Pfizer-BioNTech vaccine.

It estimated Coronavac's efficacy in real-life conditions at 54 percent -- in line with trial results in Brazil.

The Pfizer jab has been estimated to be about 94 percent effective in an Israeli study.

Chile has so far given at least one shot to 7.07 million people, and both shots to 4.04 of 15.2 million inhabitants being targeted for vaccination.

Like the rest of Latin America, the country has seen a steep rise in new infections and has surpassed the daily rate of the first wave last year, with more than 8,000 new cases per day.

"Getting vaccinated very significantly decreases the possibility of infection, it does not eliminate it, but it decreases it a lot, therefore you have to get vaccinated," University of Chile rector Ennio Vivaldi told a virtual press conference.

But it was also clear that the first dose on its own "does not have any relevant effect after four weeks" which means the recipient was for all intents and purposes just as vulnerable to infection as a non-vaccinated person.

The study estimated that for people between 75 and 79 -- targeted in the initial vaccination campaign -- there would have been 80 percent more infections without the vaccine.

For those aged 70 to 74, the percentage dropped to 60 percent.