Post-vaccine infections are to be expected, say experts

The past week has delivered a Covid-19 shocker to Singapore, not just because of the increase in community cases - there were 10 - but also the infections in people who had been vaccinated or who had been previously infected.

The Ministry of Health (MOH) said last Thursday that 17 workers residing in Westlite Woodlands dormitory who had recovered from Covid-19 infections were found to be infected again. Last night, it said 24 recovered workers at the dormitory tested positive, of which five are likely to be cases of re-infection.

Last Friday, the MOH also announced that an Indonesian seaman who had received his first vaccine dose tested positive. The next day, two more seamen who had received their first dose of vaccine were also found to be infected.

Since they had not received both vaccine jabs, their getting infected is not of great worry since they had not achieved maximum vaccine protection.

Of greater concern, however, is another man who had received both vaccine doses by March 19 and who became infected.

His parents had flown in from India on April 15. His father was diagnosed with Covid-19 on arrival and taken to hospital, while his mother was placed under quarantine. He received permission to care for her, and he was diagnosed with the disease last Saturday.

Experts that The Straits Times spoke to said such post-vaccine infections, as well as reinfections for those who had been previously diagnosed with the disease, are to be expected, even after the majority of the people here have been fully vaccinated. It is a reflection of things to come at large.

Associate Professor Hsu Li Yang, an infectious diseases expert at the National University of Singapore's (NUS) Saw Swee Hock School of Public Health, said these cases are "disappointing, but not a real shock".

He said: "We expect an average of five out of 100 Pfizer- or Moderna-vaccinated persons to come down with symptomatic Covid-19 if exposed, and 10 per 100 vaccinated persons to come down with any Covid-19 infection (asymptomatic or symptomatic) based on the clinical trials and real-world data from Israel and the United States."

In a sense, it is like measles, he said. Although 95 per cent of children here are vaccinated against it, cases still pop up.

Professor Ooi Eng Eong of Duke-NUS Medical School's emerging infectious diseases programme said that most vaccines cannot "elicit immune response to levels sufficient to prevent infection".

But those who have received Covid-19 vaccines "around the world have also shown greatly reduced risk of hospitalisation and death".

They are also less likely to spread the infection to others.

Prof Hsu explained that as these people are less sick, or totally without symptoms, they have lower viral loads, thus reducing the risk of transmission.

Viral mutations may also increase infections, Prof Hsu said. In Singapore, the most commonly isolated variant in the past month is the B1617 "Indian" variant.

As to why so many in the dormitory have been reinfected, Professor Teo Yik Ying, dean of the NUS Saw Swee Hock School of Public Health, postulated: "We have known that their living environment continues to be one of the higher-risk environments.

"That means the foreign workers living in the dormitories are always at a higher risk of being infected by someone sharing the same room or communal facilities."

Prof Ooi said people who are found to be infected but asymptomatic do not pose a problem, as they present no burden on the healthcare system.

This article first appeared in The Straits Times.