DUNDGOBI, Mongolia -- Nurse Sodkhuu Galbadrakh clutches a box of COVID-19 vaccines on his lap as he journeys along a bumpy track through a remote region of the Mongolian steppe, going home-to-home to offer booster doses to herders.

The country of three million has taken some of the world's toughest and most enduring measures against the coronavirus pandemic, shutting schools for much of the last two years and closing borders.

Its vaccination program has seen huge take-up with more than 90 percent of adults receiving two jabs.

But the booster program is seeing patchier success among nomadic communities thanks to both online misinformation and the sheer logistical challenge that comes with reaching remote communities in such a vast nation.

Mongolia is one of the most sparsely populated countries in the world and about one-third of the population are nomadic.

''During the first wave, people were queuing outside (for vaccines) and I was working until 9 pm,'' said Sodkhuu. ''There were days I didn't go home. Now, only five to six people come to get the booster shot per day.''

He said he calls herders daily to try and arrange the third shot but often can't get through, especially with poor phone reception in pastureland.

This meant health officials had no choice but to go to the herders, he added.

Mixed results

After finding several ger homes empty, Sodkhuu -- accompanied by doctor Enkhjargal Purev -- met 37-year-old herder Enkhmaa Purev, who received the booster.

''I was planning on getting my booster shot the next time I visited the soum (town) centre,'' the herder told AFP, saying she had driven 160 kilometers (99 miles) earlier this year with her husband to get their first doses.

Another herder, named Badamkhuu, couldn't get the jab due to high blood pressure -- a common problem among herders due to a high cholesterol diet.

''I had extremely high blood pressure after the second dose , so I don't want any more vaccines,'' said 65-year-old herder Dulamsuren Gombojav, who also declined the jab when offered by Sodkhuu.

According to Mongolia's health ministry, there have been 667,391 COVID cases and nearly 2,000 deaths.

Cases have plummeted since vaccines were rolled out, and Ulaanbaatar is anxious progress is not lost through jab hesitancy.

Only around 45 percent of adults have had a booster vaccine.

''Young people spread rumors or have a perception that COVID is just like flu, and they can recover easily, like the flu,'' Sodkhuu told AFP on the outreach drive.

''(They) think that they don't need vaccines or boosters.''

On the day AFP joined the medical team, they had hoped to administer booster shots to six herder families. Only three accepted.

But Batbayar Ochirbat, the official leading the vaccination program, said trust is gradually improving in the third jab.

Since September when daily cases peaked at more than 3,000, numbers have rolled down to an average of 200 daily cases, which he says is partly down to boosters.

''People started to build trust after they saw vaccinated people have booster shots, develop no symptoms, and not get sick,'' he said.