Can Covid Delta Presence be also predicted in Thailand

Wilson Chua
6 min readAug 7, 2021


I wanted to find out if the same age cutoff of cases can also signal the presence of Covid19 Delta variant in Thailand. For this experiment, I roped in my nephew, Jantzen Ang and sought the help of Chris Sobrepena. He is a Pinoy stationed in Thailand. Chris provided the link to the source data and context — since he is living in Thailand.

Data source:

The most significant 3rd wave started on April 3, 2021 which is around the 13th week of 2021.

Officially, Delta Variant was detected in mid May :

The Delta variant first hit Thailand in mid-May and spread quickly throughout the country. The first known case inside Thailand was in a Thai woman and her 4 year old son who flew into the country from Pakistan.

But the number of Covid Positive cases in younger patients say otherwise. It may have started way earlier and went undetected as early as a month before. I think we can detect it as early as April 18, 2021. At that date, the percent of NEW cases with patients 19 years and younger hit close to 10% of the new cases. Delta is known to more easily infect the younger people.

Filtering the cases for those aged 19 and below, we see the largest cluster occur in Mae Sot district with a total of 59 cases.

Why Mae Sot?

Mae Sot sits at the border between Myanmar and Thailand.

The land based theory:
Assuming that Delta variant came over land from India, the map on the right shows that it will need to cross Myanmar to reach Thailand.

Mae Sot sits at the border of Myanmar and Thailand. The migration of Burmese people into Thailand could be related to the current civil unrest there. The Burmese could have brought the Delta strain into Thailand.

Here is the Travel Pattern in March in Thailand showing only the routes with increased flows (vs pre-pandemic levels, in Blue) for week 10:

Blue Lines Indicate MORE Travel than Pre Pandemic
Travel FROM Mae Sot to the rest of Thailand shows decreased flow volumes (in Red) Week 10

Despite the decreased volume, the red lines still indicate that there was travel from Mae Sot to other areas in Thailand. The infection could have started from Mae Sot.

In fact, Thai Covid cases with Burmese nationality made up the 2nd largest group of patients. This Doughnut chart by Jantzen Ang shows the composition of Thai covid cases by Nationality:

By 17th of April, The Tak Provincial Government issued Order №1211/2564 to restrict Migrant workers’ entry and re-entry to the province. Intra-provincial travel across districts must be approved by chief of Districts in BOTH the district of origin and destination. For Inter-provincial movements, approval must be granted by the Provincial communicable disease committee.

However, one month later - at week 17 - Covid cases in Mae Sot went down. If this was indeed Delta, maybe the steps taken above were effective to control it? Sadly, at around the same time, a new cluster appeared at Bang Lamung down south. This is the tiny red spot on the map below:

Why there? Could it be foreign tourists - since Pattaya is a magnet for tourists? or could it have been spread from Mae Sot? Facebook’s Data for Good shows ZERO travel FROM Mae Sot to Pattaya for Week 15.

But by Week 17….

Decreased travel volume compared to pre pandemic levels

And at Week 21…

Increased travel volumes compared to pre pandemic levels
Travel pattern: decreased travel volumes compared to pre pandemic levels

The cases in Chon Buri could still have been carried in from Mae Sot. Additionally, we see travel FROM Chon Buri to other parts of Thailand now shows increased volumes to Bangkok:

It looks like it spread from Pattaya to Bangkok. Thai readers might know some insights or context to the above travel pattern?

Four weeks later, we see the Covid’s progression along the travel lines indicated. Covid cases spread to younger patients around Bangkok. The map below shows the areas in and around Bangkok that are affected.

This is the travel pattern by Week 21 shows overall shorter routes. But travel intra Bangkok and nearby environs is still heavy and MORE (colored blue)

At week 25 (another 4 weeks), cases start to show up in other tourist areas like Chiang Mai, and the clusters around Bangkok grew larger.

At week #31, we see proliferation of the cases centered around the Bangkok area.

Week 31. No more movement to Mae Sot! but people’s movement in Bangkok is still HIGHER than pre-pandemic levels.

Here is the close up for the Bangkok area:

Bangkok has higher density population and bore the brunt of the onslaught of the Delta Variant. As we will show later, ‘Close Contacts’ was cited as the main RISK factor.

Areas in Red have higher number of young people infected with covid. This could be a signal that DELTA could be entrenched in these areas:
Sam Phran, Phra Preadang, Bang Phli, Klong Luang, Lam Luk Ka, Si Racha and Bang Lamung

And yet we still see HIGHER movement among the Red cluster areas:

As to the Risk factors mentioned, “Close Contacts” was the highest cited risk factor:

Indeed if Delta can be more easily spread (not needing 15 minutes exposure time, but just seconds), the higher density increases close proximity encounters. The FB data shows that movement is still not curtailed. These conditions will accelerate the spread faster.

Where else might Delta spread from Bangkok?

Potential path of spread from Bangkok

Several questions are raised:
How was Covid (Possibly, Delta variant) in Mae Sot contained? Did the authorities restrict movement? Or were there added measures taken?

Will we see what happened in Pattaya also happen in the Philippines Boracay (Aklan) ?



Wilson Chua

Data Analyst, Startup Founder, Tech Columnist