Is Vaccination The Only Factor Behind Labuan’s Declining Covid-19 Outbreak?

Dr Amar-Singh HSS notes that Labuan, with nearly 10% of its population having been diagnosed with Covid-19, may have natural herd immunity conferred from widespread infection.

KUALA LUMPUR, July 30 — The government has attributed the drop in Covid-19 cases, hospitalisation, and deaths in the small island of Labuan, with fewer than 100,000 residents, to an accelerated vaccine rollout that fully inoculated nearly 80 per cent of the territory’s adult population. 

However, data shows that Covid-19 infections began declining in the week of June 8 to 14, when first-dose and second-dose vaccination coverage only reached 19.5 per cent and 13.4 per cent of Labuan’s total population respectively. 

Covid-19 mortality in Labuan began dropping from the week of June 15 to 21, when inoculation coverage with at least one dose reached 33 per cent of the total population, while 13.5 per cent of the population were fully vaccinated then. 

Crucially, Labuan, which neighbours Sabah, is the worst-hit in the country in terms of cumulative Covid-19 infections per capita. As of yesterday, about 9.7 per cent of the federal territory’s population has been infected with Covid-19 after 9,645 cumulative cases were reported, according to Ministry of Health (MOH) figures, which means a significant part of Labuan’s population could already have natural immunity to the disease. 

MOH’s official infection statistics do not include people who contracted Covid-19, but were not diagnosed due to limited testing. MOH has yet to release to the public any seroprevalence studies in Labuan or elsewhere in the country to determine the number of people who were previously infected with Covid-19 but undiagnosed.

In June, when Covid-19 incidence and mortality rates in Labuan soared to alarming rates of 1,046.2 new weekly cases per 100,000 population (equivalent to nine times the national average at 119.7 cases), and 291.2 deaths per 1,000,000 population (equivalent to 18 times the national average of 16.2 deaths per million), the central government responded by deploying a large batch of Pfizer-BioNTech’s Covid-19 vaccines to Labuan as part of an expedited vaccination drive to inoculate 60,000 adults, or about 60 per cent of their total population.  

The prevalent strain in Labuan at the time was the Delta variant, which was reported to be more transmissible compared to previous Alpha and Beta strains, requiring only five to 10 seconds of “very fleeting contact” in some cases.  

Last Wednesday, about one and a half months after Labuan started their mass vaccination programme, Vaccine Minister Khairy Jamaluddin announced in Parliament that cases in Labuan have significantly reduced, attributing the federal territory’s success to the accelerated vaccination programme that has inoculated 90 per cent of the adult population with at least one dose.

The coordinating minister of the National Covid-19 Immunisation Programme (PICK) also highlighted a decrease in hospitalisation and intensive care unit (ICU) Covid-19 cases in Labuan, though he did not give specific figures.

MOH has also been quick to attribute success in controlling Labuan’s outbreak to the inoculation programme, without acknowledging the role of natural immunity conferred by widespread infection in the small population, besides immunity from vaccination. 

Labuan’s Covid-19 Epidemic Trajectory

Labuan showed a consistent drastic decline in Covid-19 case incidence since the week of June 8 to 15, from averaging 1,244 weekly new cases per 100,000 population to 156.6 cases per 100,000 population in the week of July 20 to 26.

The reduction in cases from the week of June 8 to 15 happened despite only 19.5 per cent of the total population in Labuan getting vaccinated with their first dose and only 13.4 per cent fully vaccinated by June 15. 

While researchers at the Johns Hopkins School of Public Health estimate that herd immunity is only achieved when at least 50 to 90 per cent of the population is immune to the disease, this value may vary depending on how infectious the virus is, and the degree of physical distancing practiced by the community. 

The federal territory’s weekly Covid-19 incidence rate is now at 156.6 cases per 100,000 population, which is half the national average (307.1 cases per 100,000 population) for the week of July 20 to 26. 

Meanwhile, Covid-19 deaths in Labuan for that week were at 40.2 cases per million, 1.3 times higher than the national average (32.20 deaths per million). Earlier this month, the four-week death rate in Labuan between June 9 and July 6 was 833.33 deaths per million — almost 13 times the national average (65.47 deaths per million). 

Large-Scale Infection May Lead To Natural Herd Immunity

Senior consultant paediatrician Dr Amar-Singh HSS commented it is unlikely that the decline happened due to vaccines exclusively as all outbreak control measures have a two- to four-week delay before effects can be observed. 

“It may not be the vaccine effect so much as outbreak has been very large,” he told CodeBlue. 

He compared the situation in Labuan to what happened in India after the second wave that terrorised the South Asian nation in April and May this year, which resulted in a seropositivity rate of 67.6 per cent in the months after Covid-19 peaked in India, which meant that 67.6 per cent of the surveyed population had developed antibodies against Covid-19. 

When considered together with the statistic that 62 per cent of Indian adults were unvaccinated, it is likely that most of the infected developed their immunity naturally through infection with Covid-19 rather than through inoculation.

Dr Amar explained that something similar could have happened in Labuan, where Covid-19 could have already dispersed widely into the community and infected a large proportion of the population. This would cause them to develop a natural immunity to the virus, conferring “natural” herd immunity on the territory’s inhabitants.

Nearly 10% Of Labuan Population Officially Infected

Almost 10 per cent of the population in Labuan has been infected by Covid-19 as of July 29, since the virus was first detected in Malaysia last year in January 2020, the highest rate in the country. 

Kuala Lumpur, Negeri Sembilan, and Selangor made up the second, third and fourth highest, with Covid-19 infecting 6.7 per cent, 6.2 per cent, and 6.0 per cent of the total population in the capital city and each state respectively. 

Other states reported less than 5 per cent of their population being infected as of July 29. The national rate of cumulative infections was about 3.3 per cent of the Malaysia population.

Sarawak, Labuan Declining Outbreaks Linked With Vaccination

Senior consultant paediatrician Dr Musa Mohd Nordin, however, believes that the consistent decline in Covid-19 incidence and mortality in both Labuan and Sarawak is strongly linked to their vaccination coverage that is the highest in the country.

As of July 29, Labuan and Sarawak have fully vaccinated 54.5 per cent and 44.5 per cent of their total populations respectively.

“Sarawak and Labuan in particular has (sic) shown a persistent plunge in [incidence and death] cases. This seems to be well correlated with their better vaccine coverage,” Dr Musa told CodeBlue.

Correlation refers to the direction of relationship between two events – in Labuan’s case, the number of new cases and deaths started to decrease respectively when 20 per cent and a third of the population were covered with the first dose of the vaccine. 

A correlation between vaccine coverage and incidence and death rates does not necessarily mean that higher vaccination caused infection and mortality to fall, as correlation does not always mean causation. 

Covid-19 cases were already starting to decrease by the time Labuan received their consignment of 30,000 vaccine doses in mid-June. 

According to Labuan Covid-19 Immunisation Task Force (CITF) chairman Rithuan Ismail, the federal territory has achieved herd immunity and fully vaccinated 80 per cent of their adult population as of July 27 through the National Covid-19 Immunisation Programme (PICK). 

As of yesterday, about 91 per cent of Labuan’s adult population has received at least one dose, including 79 per cent who are fully inoculated. In terms of total population of all age groups in Labuan, 62.5 per cent of inhabitants have received at least one dose and 54.5 per cent are fully vaccinated.  

Herd immunity is achieved when most of a population becomes immune to a disease, either from vaccination or previous infection, which makes them less likely to spread the disease.

This provides protection for everyone within the community, especially vulnerable populations who are unable to receive the vaccine, such as young children.  

How Are Other States Faring With Covid-19?

Nationally, almost all other states and territories have been experiencing exponential increases in Covid-19 incidence and mortality from June 1 until July 26. 

Most of the affected states have achieved less than 50 per cent of first-dose coverage and less than 30 per cent of second-dose vaccination coverage of their total population. 

Apart from Labuan, only Sarawak and the Klang Valley (Kuala Lumpur, Putrajaya, and Selangor) have vaccinated at least half of their total population by July 26 with at least one vaccine dose.

New cases in the Klang Valley have been reaching record highs in recent weeks with little to no signs of going down. In the week of July 20 to 26, new cases within the Klang Valley  made up 60 per cent of the national total (59,903 out of 100,421 cases). 

Only Sarawak showed a steady decline in the June 1 to July 26 period from 160.7 weekly cases per 100,000 population in the week of June 1 to 7, to 96.9 weekly cases per 100,000 population in the week of July 20 to 26. 

Vaccination coverage on June 7 was 8.9 per cent of Sarawak’s total population for the first dose and 4.4 per cent for 2nd dose. Eight weeks later, these figures shot up to 59.2 per cent and 41.6 per cent for the first and second dose respectively by July 26, amid Sarawak’s aggressive vaccination campaign. 

However, Dr Amar cautioned: “I think the vaccines are working in Sarawak, but you need to watch the Delta wave happening in Kuching,” referring to recent reports of Sarawak recording the highest number of Delta cases within the country. 

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