England’s care minister Helen Whately was asked this week what lessons the government has learned to prevent care home deaths on the scale we saw in “March/April” 2020. She replied:
“We didn’t know back then […] about the asymptomatic transmission of the virus and that people could be infectious even if they didn’t have the virus symptoms.”
“We also didn’t know that you could test people then – we thought the test only worked if you had symptoms. Now what we know is that the test can pick people up whether or not they have symptoms.”
Let’s take a look.
When did we know people without symptoms could spread covid?
On 28 January 2020, the government’s SAGE experts said: “There is limited evidence of asymptomatic transmission, but early indications imply some is occurring.”
A study published in the Lancet on 24 February 2020 said two individuals tested positive for coronavirus a day before feeling ill, “suggesting that infected individuals can be infectious before they become symptomatic”.
NHS guidance for clinicians from 3 March recommended: “A person that is asymptomatic […] with a Coronavirus travel history or contact with a confirmed coronavirus case” should be “advised to stay indoors” and “avoid contact with other people”. The implication is that even those who do not currently have symptoms could have the virus and infect others.
The evidence continued to mount up through March.
On 8 March, researchers in Belgium and the Netherlands estimated that 48 per cent of cases in clusters from Singapore and 62 per cent of those in Tianjin, China were the result of “pre-symptomatic transmission” – where the person passes on the virus before they develop symptoms.
On 12 March, the European Centre for Disease Control said: “In addition to case reports, pre-symptomatic transmission has been inferred through modelling” (though it said it wasn’t yet clear how much this contributed to spread).
On 27 March, a draft study of care home residents in Washington state was published by the US Centre for Disease Control. The researchers found “approximately half of all residents with positive test results did not have any symptoms at the time of testing”. They warned “unrecognized asymptomatic and pre-symptomatic infections might contribute to transmission in these settings” and recommended care homes take steps to prevent coronavirus entering their facilities.
Despite this, the UK government recommended in guidance issued to care homes in England on 2 April that: “Residents may also be admitted to a care home from a home setting. Some of these patients may have COVID-19, whether symptomatic or asymptomatic.”
On the same day, a World Health Organization (WHO) situation report stated that “some infected persons can be contagious” in the pre-symptomatic phase of the virus and that “transmission from a pre-symptomatic case can occur before symptom onset”.
And a study published by US and Israeli researchers, also on 2 April, said of coronavirus: “it is common to be contagious before symptoms” and “a large fraction of infections occur pre-symptomatically, that is, without the infectious person realizing they have the disease”.
It’s fair to say that many of these studies were not perfect. Estimates of the scale of symptom-free transmission have continued to be revised, and in some individual case reports, the researchers hadn’t always ruled out other possible sources of infection. But there was mounting evidence from multiple sources by March that people could transmit the virus without having symptoms.
When did we know tests could detect asymptomatic cases?
We’re not sure why the minister said that in March and April, “we thought the test only worked if you had symptoms”.
Most of the evidence we’ve already looked at for asymptomatic and pre-symptomatic transmission was only collected because scientists compared a person’s positive test result with their (lack of) symptoms.
As the February Lancet paper spells out, the patients involved had “positive results on RT-PCR [lab tests] a day before onset” of symptoms.
A spokesperson for the Department for Health and Social Care told FactCheck:
“Our priority from the outset has been to protect the NHS and save lives and we have taken advice from scientific and medical experts throughout.
“Covid-19 is a new virus and at the start of the pandemic, the evidence for asymptomatic transmission was still limited. As new evidence has emerged, we have adapted our approach and taken swift action to try and stop the spread of the virus, including by introducing rapid community testing.
“As the Care Minister made clear, we are carrying out extensive testing in care homes to help identify asymptomatic cases and break the chains of transmission.”
England’s care minister Helen Whately claimed “we didn’t know” in March and April 2020 that “people could be infectious even if they didn’t have the virus symptoms”.
But SAGE papers show we had early indications of “asymptomatic transmission” in late January. On 12 March, the European Center for Disease Control said people could pass on the virus before they develop symptoms – though the precise extent of this type of spread wasn’t yet known.
Ms Whately also said we “didn’t know that you could test people then – we thought the test only worked if you had symptoms”. But we knew that PCR lab tests worked on those without symptoms at least as early as February because a study found “pre-symptomatic” cases by looking at people with positive test results.