Why must I have a PCR test, and how safe is it to see my family?

Q

I have had three positive lateral flow tests – do I really need to do a PCR test?

A

If you test positive with multiple lateral flow tests, it is almost certain you have Covid, but that does not mean you shouldn’t do a PCR test.

Lateral flow devices, the rapid at-home kits, are not perfect. A third of people with Covid are thought to receive a false negative from a lateral flow test, which is why the Government recommends doing several each week.

But studies carried out by NHS Test and Trace found that fewer than one in every 1,000 lateral flow tests which come back positive for Covid were in fact negative. So the chances of three tests giving false positives are tiny.

PCR tests are viewed as the

‘gold standard’ because they are analysed in laboratories, meaning they are highly unlikely to return a false negative result.

Many positive PCR tests are also sequenced, which means that scientists are able to diagnose which Covid variant it is.

Q

We’ve all had our boosters, so is it safe to have my family over for Christmas?

A

Yes, but it is still important to take precautions.

Data published by Pfizer last week shows that three doses of its vaccine are likely to provide just as much protection against the Omicron variant as two doses did against the Delta variant.

Experts believe three doses of the others vaccines will have a similarly robust effect, although the final data is yet to arrive.

Crucially, scientists point out that even three vaccine doses do not provide total protection against severe illness from Covid.

Previous studies found that ten per cent of people who had two doses of the vaccines will still end up in hospital and may even die. The same pattern is to be expected with Omicron. It also takes roughly two weeks following a booster to get the full benefit.

So it is recommended that lateral flow tests are taken before social events. Professor Danny Altmann, an immunologist at Imperial College London, said: ‘I cannot stress enough the importance of lateral flow tests over Christmas.

‘We can’t predict who will be vulnerable to the virus, so we’ve got to take precautions to stop people getting it in the first place.’