During a live interview with Editor in Chief of TOC Terry Xu on Saturday (15 May), Prof Paul Ananth Tambyah —who is also a Senior Consultant, Division of Infectious Diseases, Department of Medicine, National University Hospital answered some COVID-19 related questions from the public such as whether air purifiers are effective in preventing COVID-19, whether it’s ok to get two different vaccinations, and more.
Question: Is it possible to have a false negative for COVID a few days? And then after a few days to be tested positive If so, how often should PCR be done?
Prof Tambyah: Yeah. So this has actually been the case with a number of [the cases in the] TTSH cluster. The first test is negative. Then the second test, a few days later, is positive. But by the time they are symptomatic usually the second or third day, they are positive.
So, as I mentioned earlier, the PCR is not a hundred per cent sensitive and it depends on your clinical judgment. So if the patient is still having symptoms, if the fever won’t go away, then you should certainly do a second or third test.
And as I mentioned, there’s a publication from TTSH, NCID where they showed you needed to test somebody four or five times before you found out that they actually did have COVID.
Question: How useful is the air purifier in an indoor office or classroom?
Prof Tambyah: I’m not a fan. You know, as I mentioned earlier, there are two schools of thought in the medical and scientific: the close contact versus the airborne, and I’m more the close contact side.
But on the other hand… the purifier removes a lot of the dust particles, and so maybe, you know, it reduces people from sniffing and sneezing. So if the guy has a mild COVID and you prevent him from sneezing, you’re preventing him from spreading the virus all over the place. So, from that point of view, rather than from the point of view of just specifically killing the virus. I think, you know, just probably a small benefit, but not a huge amount.
Question: Can the virus stay alive on food surfaces?
Prof Tambyah: So this is a very controversial thing, and this came up during the WHO visit to China to study the origins of the virus. Because the PRC government is trying to argue that this virus came from outside on frozen food and went into China.
Now there’s no evidence that the virus can spread from frozen food and infect people.
They can find the virus on frozen food. In fact, there was a study that was subsequently retracted from Singapore, where they showed that you could culture the virus on frozen food for a very long time… and the virus has been found on frozen and meatpacking plants in the US.
But whether it’s from an infected person infecting the food or the food affecting the person, it tends to be more person spreading the virus, shedding virus onto the food. And whether the virus can go on to infect somebody from frozen food is it’s still not proven.
It’s not impossible, but I would say it’s relatively unlikely…
Question: What’s your thoughts on Sinovac?
Prof Tambyah: Yeah, like I said, you know, if Sinovac was the vaccine, the killed vaccine is made by any other company, which has a track record of exporting vaccine, I would be the first in line for it.
Sinovac has tried to get Singapore regulatory approval for a very long time, and it still has not been approved by HSA. So that is a concern because HSA is quite stringent. They follow international standards and they require primary data, which they review.
So I wish that Sinovac would have that data because there seems to be real-world evidence from like Indonesia where they’ve used Sinovac, and it seems to be relatively effective and in what they have done.
But again, we haven’t seen published data and the peer-review literature, and we haven’t seen data that satisfied HSA. So that’s a pity.
I know many older people, you know, like I said, people get vaccinated for travel and China says the only accepts Sinovac or Sinopharm, so they are waiting for Sinopec to get approved, but it’s taking a really long time. And so, you know, I hope that they will just provide the data and then we’ll get the approval soon.
Question: So where does the delay come from?
Prof Tambyah: Yeah, my understanding from the last HSA statement is that they’re asking Sinovac for data and Sinovac hasn’t provided them the data. So, the data is from that end. That’s my understanding again, based on the public documents that have come up.
Question: So say a person has received two of the Pfizer jabs, but then later decides he wants to take Sinovac. Is that ok?
Prof Tambyah: Well right now there are a few things. One, Sinovac is not licensed in Singapore. Two, the vaccines are free, so they’re not going to pay for a third job. So you probably have to wait until it becomes commercially available.
And that would be like a booster.
Theoretically, there’s no good reason why it shouldn’t work. And in fact, there are studies being done in the UK where they’re doing this mix and match of AstraZeneca and Pfizer and trying to see whether that they work.
