Most healthy Thai children under five have already contracted Covid-19 and developed natural immunity, suggesting vaccination may not be necessary for this age group, according to Dr. Yong Poovorawan, Head of the Center of Excellence in Clinical Virology at Chulalongkorn University in Thailand.
In a Facebook post on 2 May, Yong cited findings from a recent large-scale study involving 830 healthy children aged six months to four years.
“This research highlights how COVID-19 has become a typical respiratory virus, infecting most children early in life,” he wrote.
Conducted between May and August 2024 in Ayutthaya, Uttaradit, Buri Ram, and Trang, the study found that by age one, about 80 percent of children had been infected with COVID-19. By ages three to four, nearly all had been infected, despite most never receiving a vaccine.
Testing showed the presence of anti-N antibodies, confirming prior infection, and many children also had neutralizing antibodies against the JN.1 variant, the dominant strain during the study period. Their immunity also showed some cross-protection against the original Wuhan strain, though to a lesser extent.
While JN.1 symptoms are similar to other Omicron-based variants, it is more transmissible and was the dominant global strain at the time. The Thai doctor noted that JN.1 is no longer circulating. The current dominant variant in Thailand is XEC, a recombinant subvariant in the Omicron lineage.
XEC has become the most commonly reported SARS-CoV-2 subvariant globally and is spreading widely. Although COVID-19 mortality has declined, it remains a significant cause of hospitalizations and deaths, especially among vulnerable groups. Despite this, vaccines available in Thailand still target the now-outdated JN.1 variant.
Given most young children have already been infected, often with mild or no symptoms, Dr. Yong suggested routine vaccination for healthy children under five may not be necessary. Infants under six months, he added, receive some protection from maternal antibodies.
The study was funded by the Health Systems Research Institute (HSRI). Dr. Yong also noted upcoming findings on “imprint immunity,” or immune memory shaped by early exposure, in older children and adults.