Friday 23 April 2021

COVID-19 antibody levels wane in some recovered patients over time; Post-COVID-19 vaccine infections and reinfections could happen, say experts

By Toh Ting Wei, The Straits Times, 23 Apr 2021

Recovered Covid-19 patients have shown immune response to the coronavirus for "well above" 300 days. Still, studies done by the National Centre for Infectious Diseases (NCID) found that the Covid-19 antibody levels in some of the patients do wane over time.

That makes it possible for someone who has recovered from the virus to be reinfected later, said the Health Ministry's director of medical services, Associate Professor Kenneth Mak.

He explained yesterday that many of the recovered migrant workers in Singapore have reached the 300-day milestone after being infected with Covid-19. "It is now prudent for us to start monitoring very closely for the risk of reinfection taking place," said Prof Mak. This includes placing recovered migrant workers in the dormitories back into a rostered Covid-19 testing programme, 270 days after their past infection.

Similarly, such stepped-up monitoring should also apply to travellers who enter Singapore, Prof Mak added.

Concerns about reinfection of recovered Covid-19 patients increased this week after the Ministry of Health reported that 17 recovered workers at Westlite Woodlands dormitory tested positive for the coronavirus.

They were tested after a 35-year-old Bangladeshi staying there was confirmed to have the coronavirus on Monday. The workers have been sent to the NCID, where an expert panel will investigate further as to whether these are reinfections.

Prof Mak said: "NCID will need more time to establish if these are prolonged shedding from old infections or they are indeed reinfection cases."

The investigations would usually take about two to three days, but up to two weeks in some cases, he added.

Migrant workers in dormitories form the bulk of the 60,904 Covid-19 cases in Singapore.

About 8,000 workers from the construction, marine and process sectors have received the first dose of the Covid-19 vaccine. Meanwhile, 34,000 workers in those sectors have received both doses.

COVID-19 protection may last up to 18 months with vaccine: Associate Professor Kenneth Mak
Another vaccine dose may be needed if person's immunity wanes or to guard against new variants, says MOH director
By Toh Ting Wei, The Straits Times, 23 Apr 2021

Individuals vaccinated against Covid-19 may be protected for up to 18 months.

Beyond that, additional vaccination shots might be needed if a person's immunity to the virus begins to wane, the Ministry of Health's (MOH) director of medical services Kenneth Mak said yesterday.

Another jab could also be required to guard against new variants of the coronavirus, he added in response to a question at a virtual news conference on plans to administer a third dose of the vaccine.

Associate Professor Mak said: "At this point in time, there is quite a bit of thought that the vaccinations should be able to last us for at least nine months to 12 months.

"We believe that it is going to be much longer than that, perhaps even 15 to 18 months. But beyond that, it is still a relatively uncertain situation."

Prof Mak said the immunity accorded by the vaccines could wane, just like how recovered patients have gradually reduced protection against the virus.

The authorities will conduct follow-up tests on some of the people who have been fully vaccinated, he said, adding: "If we find that their immune levels start to drift downwards, it would then be the right time to start planning to vaccinate these people as well."

He also noted that while the Pfizer-BioNTech and Moderna vaccines are effective in protecting against current Covid-19 variants, Singapore has to prepare for the possibility that they may not be as effective against future variants.

"If that were the case, it may well be the case that we need booster vaccine doses to augment the immunity that we already have from the previous vaccinations and to give us additional protection, particularly against these variants of concern," he added.

Singapore is studying the issue and has discussed it with other countries, said Prof Mak.

The vaccine manufacturers are looking into it as well, he added, and hope to produce vaccines to guard against new variants of the coronavirus.

"Where such a product is available, we may plan to make that available as booster doses in the population that had previously been vaccinated," said Prof Mak.

As at April 18, more than 2.2 million doses of Covid-19 vaccines have been administered in Singapore. Almost 850,000 people have received both doses.

Health Minister Gan Kim Yong said yesterday that the Republic continues to make steady progress in its vaccination programme.

Thirty-eight vaccination centres have been set up, on top of 20 polyclinics and 22 Public Health Preparedness Clinics offering jabs.

Two other vaccination centres will be set up by this week.

Mr Gan said he was encouraged by the response of Singaporeans to the vaccination programme.

"However, our supply remains limited, given the global shortage," he noted.

"I therefore encourage all medically eligible Singaporeans and long-term residents to go for vaccination when it is offered to you."

*  Recovered workers who test positive for COVID-19 may not be reinfected, could be shedding viral fragments, which are non-infectious: Ministry of Manpower
By Hariz Baharudin, The Straits Times, 29 Apr 2021

Not all recovered workers who test positive for Covid-19 may have been reinfected as they could just be shedding viral fragments from an old infection, said the Ministry of Manpower (MOM) yesterday.

More recovered workers are expected to test positive for the coronavirus as the authorities conduct regular testing of those who were infected more than 270 days ago, due to the risk of waning immunity and the threat of new variants.

Dr Lam Meng Chon, medical director of MOM's Assurance, Care and Engagement Group, said such cases will require further clinical assessment over several days to determine whether they are old or current infections.

"When Covid-19 positive cases are found among the recovered workers population, it does not mean that it is a confirmed cluster because it could actually be a group of people who are shedding dead viral fragments, which are actually non-infectious," he told reporters on the sidelines of a briefing.

"In this case, it is not a cluster but an old infection. So there is no need to panic, but to actually be patient and allow the clinical assessment to take place."

Dr Lam was referring to the 24 recovered workers at Westlite Woodlands dormitory who tested positive for Covid-19. Of this group, five were determined to be likely cases of reinfection, while 11 were assessed to be shedding virus fragments. Two of them tested negative upon retesting, while the remaining six cases are pending assessment by an expert panel.

On April 22, Associate Professor Kenneth Mak, the Health Ministry's director of medical services, said investigations to establish if a person is a reinfection case usually take about two to three days, and up to two weeks in some cases.

Yesterday, MOM said movement restrictions or quarantines in dormitories might be imposed if a few workers there test positive for Covid-19. Such measures are necessary while the clinical assessment is carried out and will be lifted when testing is completed, the ministry added.

MOM said: "If quarantines are imposed in some dormitories, this does not necessarily mean that there are confirmed clusters there. Most of the time, it is because cases are being assessed to determine if they are old or current infections."

Dr Lam said imposing a quarantine will allow the authorities to quickly isolate cases of reinfection and prevent further spread.

He set out two scenarios for recovered workers who test positive in PCR tests.

One: the person is a prolonged shedder of Covid-19 and does not pose a threat to public health as he is non-infectious. Two: the person is a reinfection case, which means he got infected with a different Covid-19 strain.

In the second case, the person is infectious and poses a risk of spreading the virus to others, Dr Lam said. Measures must thus be taken to curb further transmission.

There is no need for the public to be worried as the appropriate public health measures will be put in place early, he added.

Asked how workers will be taken care of should they be quarantined while clinical assessments are taking place, he said their well-being is of utmost importance to MOM.

He outlined several steps MOM has taken, including distributing care packs to workers and providing timely updates on a smartphone app for foreign workers.

"Beyond this, we are also working with the various non-governmental organisations such as HealthServe and Migrant Workers' Centre to help assure the workers who are quarantined at this moment," Dr Lam said.

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